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[Display omitted] • Novel Pd 4 Ir 1 /DMSNs-NH 2 catalyst with dendritic morphology and highly dispersed PdIr NPs was prepared. • The dendritic morphology of the Pd 4 Ir 1 /DMSNs-NH 2 catalyst can promote the mass transfer of the reactants and products. • The small particle size (200 nm) of the Pd 4 Ir 1 /DMSNs-NH 2 catalyst can increase the accessibility of the reactants to the active sites. • The ultrafine size (2.1 nm) and high dispersion of PdIr NPs could expose more catalytic active sites. • The Pd 4 Ir 1 /DMSNs-NH 2 catalyst presents an initial TOF value of 1333 h−1, 100 % H 2 selectivity, and excellent stability at 298 K. Developing highly efficient solid catalysts for formic acid (HCOOH, FA) dehydrogenation is essential to utilize FA as a hydrogen (H 2) carrier. In this work, ultrafine bimetallic PdIr nanoparticles (NPs) supported on the amine-functionalized dendritic mesoporous silica nanospheres (PdIr/DMSNs-NH 2) have been successfully synthesized by the simple surface functionalization and co-reduction method. The optimized Pd 4 Ir 1 /DMSNs-NH 2 (Pd/Ir molar ratio = 4:1) catalyst displayed the remarkable catalytic performance with 100 % H 2 selectivity of the FA dehydrogenation, and the initial turnover frequency (TOF) could achieve 1333 h−1 with the additive of sodium formate (SF) at 298 K, which is comparable to the most effective mesoporous silica supported Pd-containing solid catalysts. The activation energy (Ea) for the FA dehydrogenation of Pd 4 Ir 1 /DMSNs-NH 2 catalyst in the FA-SF mixture is 39.7 KJ/mol, lower than most reported catalysts. Furthermore, the optimized catalyst maintained 100 % H 2 selectivity even after five runs, only with a negligible decrease in the activity, displaying the excellent stability of the catalyst. The superior catalytic performance could be attributed to the synergistic effect of open dendritic pore channel, high dispersion and ultrafine size of PdIr NPs as the active sites on DMSNs-NH 2 , and regulated electronic effects of Pd and Ir. More importantly, introducing –NH 2 groups to the DMSNs could facilitate the O–H bond dissociation of FA and improve the FA dehydrogenation activity under mild conditions. This work will significantly promote FA as a hydrogen carrier on fuel cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • MXenes are efficient in promoting the epitaxial growth of bulk Pt to form Pt ATNLs. • Geometric and electronic effects of MXenes change adsorptive properties of Pt ANTLs. • Pt ANTLs on MXenes show high propylene selectivity and anti-coking ability in PDH. • MXenes downshift d-band center of Pt ANTLs leading to improved performance in PDH. Contradiction between catalytic activity and coking-resistivity of propane dehydrogenation (PDH) has been a major concern. Here, the potential of using pristine MXenes as supports in stabilizing Pt atomically thin noble metal layers (ATNLs) for catalyzing PDH was evaluated by first-principles calculations and microkinetic simulations. Various electronic structure analyses demonstrated that the MXenes could stabilize Pt ATNLs via strong metal–metal bonding, leading to expanded Pt lattice constants, and accumulated electron density on Pt. Consequently, MXene-supported Pt ATNLs favored propylene desorption over further dehydrogenation, contributing to higher propylene selectivity and anti-coking ability. In particular, the Pt ATNLs on Mo 2 C and W 2 C showed comparable activity with the pure Pt (1 1 1) surface, but might improve the anti-coking ability by 4 to 6 orders of magnitude. Finally, propylene binding strength, which could be explained by the d-band theory, was identified as an effective indicator in determining PDH reactivity and anti-coking ability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bimetallic NiCu catalysts of various Cu:Ni ratios were deposited on and within a Zr-based metal–organic framework (MOF) NU-1000. • Increasing Ni concentrations resulted in lowered apparent activation energy for non-oxidative ethanol dehydrogenation. • The presence of Ni was beneficial for stabilizing catalytically active species. • Ni also actively participated in catalysis as a hydride former. Non-oxidative ethanol dehydrogenation is a promising route to produce acetaldehyde and hydrogen from sustainable feedstock. Bimetallic NiCu catalysts have shown high efficiency and selectivity for this chemical transformation. In this study, we leverage the high porosity and uniform catalyst deposition sites on a Zr-based metal–organic framework (MOF) catalyst support, NU-1000, to understand how the changes in Cu:Ni ratio affects the reactivity for non-oxidative ethanol dehydrogenation. We found that increasing the Ni2+ concentration significantly reduces the activation energy of the reaction due to the role of Ni2+ in suppressing the onset of Cu reduction. This study illustrates how MOFs can be used as catalyst supports to fine-tune the catalyst compositions and understand their effect on the overall catalytic performances. [ABSTRACT FROM AUTHOR]

[Display omitted] • [Ni(en) 3 ](NO 3) 2 is a better precursor of nickel than Ni(NO 3) 2. • Nickel dispersion can be improved by the coordination nickel precursor. • As-synthesized catalyst with less metal, but has better performance. A bimetallic Ni-Pt catalyst (6Ni-Pt-HMS) was designed for the dehydrogenation of 1,2-cyclohexanediol (CHD) to catechol. The hexagonal mesoporous silica (HMS) as support, loaded with platinum and nickel by one-pot and incipient-wetness impregnation method, respectively. [Ni(en) 3 ](NO 3) 2 is used as the precursor of nickel. The physi-cochemical properties of the catalysts were examined by XRD, BET, SEM and TEM techniques. The effect of ethylenediamine on nickel dispersion during impregnation was studied by comparing with the traditional precursor (nickel nitrate). FTIR and TGA results showed that the presence of ethylenediamine modifies the behavior of nickel during impregnation and calcination. The activity and stability of the catalysts were evaluated on a fixed-bed, revealing the influence of mesoporous structure, ethylenediamine, and platinum on reaction. The 6Ni-Pt-HMS catalyst, with the conversion of CHD is 100 %, the selectivity of catechol as high as 99.7 % with the liquid hourly space velocity (LHSV) is 9 h−1, and a long-term stability. The deactivation mechanism of the spent catalyst was analyzed by BET, TGA, SEM, TEM-EDX and ICP-OES. [ABSTRACT FROM AUTHOR]

[Display omitted] • Approach for anchoring of Pt atoms on isolated Sn4+ is introduced. • Using this approach PtSn/SiO 2 (hexagonal mesoporous silica) catalysts were prepared. • Pt-Sn/atoms/sub nanoclusters were identified on the surface of catalysts. • The catalysts are active, selective, and stable in C 3 H 8 dehydrogenation to C 3 H 6. • Sn is essential to enhance H 2 desorption from Pt that is the rate-limiting step. Owing to propane availability in shale gas and the growing demand for propene, non-oxidative dehydrogenation of this alkane has attracted much attention. Although, catalysts with supported PtSn species are applied on the large scale, a further increase in their activity without loss in propene selectivity at low Pt content would certainly improve process economy. Herein, we introduce a molecularly defined strategy for controlling catalyst activity through anchoring of Pt atoms on isolated Sn4+ firmly confined in the framework of hexagonal mesoporous silica. In addition to the dispersion of Pt species, the presence of Sn4+ in close contact with Pt is essential for increasing the rate of propane dehydrogenation through enhancing H 2 desorption, which is the rate-limiting step. As the anchored Pt atoms/sub nanoclusters do not sinter under reducing conditions, the developed catalysts show high on-stream stability and propene selectivity of above 99 % under industrially relevant conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Selective transformation of HMF to DFF and H 2 is appealing yet still challenging. • Pt/CdS was efficient for dehydrogenation of HMF to DFF under visible light. • Strong interaction between furan ring in HMF with Pt NPs promotes this reaction. The selective transformation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) with coproduction of hydrogen under visible light is appealing yet still challenging. In this manuscript, Pt/CdS nanocomposites obtained via photoreduction of [PtCl 6 ]2- over CdS were found to be an efficient and chemoselective photocatalyst for dehydrogenation of HMF to produce DFF under visible light, with simultaneously generation of stoichiometric hydrogen. An optimum performance was observed over 1.0 wt% Pt/CdS nanocomposite, with a complete conversion of HMF to DFF and stoichiometric hydrogen generated in 14 h. By comparison with the performance over MoS 2 /CdS, it is revealed that the superior performance for photocatalytic dehydrogenation of HMF over Pt/CdS should be ascribed to the strong interaction between the furan ring in HMF with Pt nanoparticles (NPs), which enables the protons released from HMF to fast transfer to Pt NPs in close vicinity for further reduction to generate hydrogen. This study provides an efficient and green strategy for the simultaneous transformation of biomass-derived HMF to DFF and the production of clean energy hydrogen. This work also highlights the great potential of photocatalysis in biomass valorization. [ABSTRACT FROM AUTHOR]

[Display omitted] • The first MOF catalyst was developed for the alcohol dehydrogenation to carboxylates. • The Zn-based MOF catalyst was prepared in a facile and environmental-friendly manner. • The catalyst could be reused at least 5 consecutive times without activity decay. • Aldehyde as a key intermediate and [Zn-N] as the active sites were proposed. Zeolitic imidazolate framework-8 (ZIF-8) is a representative Zn-based metal–organic framework (MOF) featuring high porosity, good stability, and large surface area. Owing to these fascinating properties, ZIF-8 exhibits promising potential in catalysis. With our continuous interest in catalyst development of alcohol-involving green transformations, we intended to exploit the capability of ZIF-8 in catalyzing the acceptorless dehydrogenation of alcohols to carboxylates. The preparation of ZIF-8 at room temperature possesses advantages such as environmental friendliness and easy operation. Subsequently, various techniques were adopted to characterize the structures, morphology, and chemical states of both fresh and reused catalysts. Notably, the catalyst displayed good reusability since it could be reused at least 5 times without considerable loss of catalytic activity. It was also perceived that KOH was an indispensable component of this catalytic process. More specifically, KOH not only worked as one of the starting materials but also provided the basic environment to promote this catalysis. Furthermore, the aldehyde was confirmed as a key intermediate for this catalytic process. Based on additional experiments and literature reports, we proposed [Zn–N] as the active sites and presented a plausible catalytic cycle. [ABSTRACT FROM AUTHOR]

[Display omitted] • The first example of amide preparation by a tandem reaction of bimetallic cooperative catalytic amine acceptorless dehydrogenation and oxygen transfer of DMSO. • A plausible amide formation mechanism in which one Ru center combines with N atom of the mine and the other coordinate with the S atom of DMSO to enhance the transfer of oxygen of DMSO to amine to give amide has been proposed, • The role of DMSO was successfully demonstrated with the help of NMR, HRMS, IR, and D- and 18O-isotopic labelling studies. • Higher catalytic activity and selectivity, good functional groups tolerance. We have developed a new catalytic system for preparing amides by tandem acceptorless dehydrogenation of amines and oxygen transfer of DMSO. This system shows very good catalytic activity and selectivity, a variety of primary amines and even diamines are converted into the corresponding amides in good to quantitative yields (>99 %). The unprecedented catalytic performance of this binuclear ruthenium complex was attributed to a unique chelating model wherein one Ru center combines with N atom of RCH NH produced from the dehydrogenation of RCH 2 NH 2 and the other co-ordinates with the S atom of DMSO, thus bringing the DMSO and imine molecules into proximate to enhance the efficiency of the oxygen transfer from DMSO via a six-membered ring transition state. The mechanism study indicated that the oxygen in the product amides came from DMSO and C H bond cleavage in DMSO was the rate determining step. [ABSTRACT FROM AUTHOR]

[Display omitted] • Potential propane dehydrogenation (PDH) pathways over Ga hydride species trapped by Al-pairs in Ga/ZSM-5 were investigated. • These in-situ formed undercoordinated Ga hydride species are preferred for PDH. Undercoordinated b[GaH]2+ would exhibit PDH activity superior to other Ga species. • The most plausible PDH pathway over undercoordinated b[GaH]2+ is the carbenium pathway. • Ga hydride species evolves as the PDH proceeds. Ga/ZSM-5 is widely used to catalyze propane dehydrogenation (PDH). For the harsh operation conditions, the detailed active species, and the plausible reaction pathways that are responsible for the observed superior PDH performance remain unresolved for Ga/ZSM-5. Reduced extraframework Ga hydride species trapped at zeolite framework Al-pairs, including b[GaH]2+, [Ga]+-BAS, [GaH 2 ]+-BAS, etc. are an important kind of Ga species known as active species for PDH. In this work, the PDH pathways these over these Ga species were investigated theoretically at temperatures and pressures relevant to experiments. We showed that dynamically generated undercoordinated b[GaH]2+ would exhibit significantly higher catalytic activity at PDH conditions as compared with other Ga hydride species. The most plausible PDH pathway over b[GaH]2+ is the carbenium pathway. The Ga species and BAS act in concert in promoting the H 2 elimination and β-H transfer, and in turning PDH efficient. Ga hydride species may also form as intermediates along the PDH pathways as active sites for subsequent activation and conversion of propane, suggesting the evolution of Ga hydride species trapped by Al-pairs in Ga/ZSM-5 at operation conditions. The findings are expected to pave the way for better understanding of the experimentally observed operation condition dependent PDH performance of Ga/ZSM-5. [ABSTRACT FROM AUTHOR]

A facile manganese-catalyzed three-component phosphinomethylation of indoles and naphthols using methanol as a sustainable C1 source and an acceptorless dehydrogenation strategyis reported. A set of indoles, naphthols, and phosphines with different substituents could undergo the acceptorless dehydrogenative cross-coupling efficiently and furnish the corresponding C–H phosphinomethylated indoles and naphthols in moderate to good yields. [Display omitted] • Manganese-catalyzed phosphinomethylation of indoles and naphthols using an acceptorless dehydrogenation strategy. • Key features of our development include (a) the first example of C–H phosphinomethylation of indoles/naphthols, (b) the use of a stable, non-noble manganese catalyst, (c) high atom- and step-economy, (d) using methanol as a C1 source, (e) the side-products are "green" (H2O and H2), and (f) a broad substrate scope. We here report a facile manganese-catalyzed three-component phosphinomethylation of indoles and naphthols using methanol as a sustainable C1 source and an acceptorless dehydrogenation strategy. A set of indoles, naphthols, and phosphines with different substituents could efficiently undergo the acceptorless dehydrogenative cross-coupling and furnish the corresponding C–H phosphinomethylated indoles and naphthols in moderate to good yields. Mechanistic studies indicate that this transformation proceeds with the dehydrogenation of methanol to form a formaldehyde-coordinated manganese species as the key intermediate. [ABSTRACT FROM AUTHOR]

[Display omitted] • PdZn/TiO 2 has the excellent performance of transfer hydrogenation using HCOOH. • HCOOH is dehydrogenated on PdZn/TiO 2 mainly through the carboxyl pathway. • Mutil-atomic Pd ensemble is identified as the active site of transfer hydrogenation. • Nearly all hydrogen atoms of HCOOH catalyzed by PdZn/TiO 2 can be available. HCOOH dehydrogenation is closely related to many importantly strategic reactions, including the fields of transfer hydrogenation, chemical hydrogen storage and C1 chemistry-related transformations, and so on. In the present work, it is found that HCOOH dehydrogenation on PdZn/TiO 2 is dominated through the rarely reported carboxyl pathway. The multi-atomic Pd ensembles of PdZn/TiO 2 are determined to be the active sites for low temperature transfer hydrogenation. Moreover, nearly all hydrogens of HCOOH catalyzed by PdZn/TiO 2 are confirmed to participate in the low temperature transfer hydrogenation of p -nitrophenol. Conversely, Pd/TiO 2 only can catalyze half of the proportion of hydrogen of HCOOH through the formate pathway. The carboxyl pathway-dominant HCOOH dehydrogenation on PdZn/TiO 2 results in accumulation of fewer intermediate species and generation of more active hydrogens, consequently boosting the low temperature transfer hydrogenation activity using HCOOH. [ABSTRACT FROM AUTHOR]

[Display omitted] • An in-situ synthesis strategy for attaining well-dispersed and ultra-small Cu nanoparticles (∼1.8 nm) encapsulated within silicalite-1. • A highly active, selective and durable catalyst (Cu@S-1) for the dehydrogenation of ethanol to acetaldehyde. • Zeolite encapsulation could achieve and maintain a prevailing proportion of the active Cu+ species. • Zeolite encapsulation could prevent the quick deactivation induced by the facile sintering of Cu species during catalysis. The selective dehydrogenation of ethanol to acetaldehyde is one of the pivotal reactions for biomass valorization, wherein the well-defined and robust Cu-based solid catalysts are highly desired for potential practical application. Herein, ultra-small Cu metal nanoclusters (∼1.8 nm), encapsulated inside Silicate-1 (S-1), have been successfully fabricated by an in-situ approach. The as-synthesized Cu@S-1 catalyst shows a near quantitative ethanol conversion, a good acetaldehyde selectivity up to ∼90 %, and more importantly an excellent stability with no apparent deactivation even after a TOS of 110 h in the continuous dehydrogenation of ethanol to acetaldehyde at 523 K. Comprehensive and thorough characterization studies reveal that the spatial constraint environment of the zeolite could not only efficiently restrict the movements of Cu entities, which thus prevents the metal sintering during catalysis, but also induce a predominant amount of well-retained Cu+ species (up to ∼70 %) that play an essential role for the enhanced performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mesoporous sulfur-decorated Pt–Al 2 O 3 is made by solvent-deficient precipitation. • The best dehydrogenation activity is achieved at the sulfur content of 0.21 wt%. • The electron density of Pt atoms is lowered by the neighbors of sulfur added. • The sulfur added weakens the adsorption of dehydrogenation products on Pt atoms. • The amount of H 2 adsorbed is in a volcano-shaped dependence on the sulfur content. The addition of sulfur to supported Pt catalysts often regulates Pt defect sites causing side reactions, where the interaction between Pt and sulfur depends on catalyst preparation methods. Herein, we report the solvent-deficient precipitation (SDP) to afford mesoporous sulfur-decorated Pt–Al 2 O 3 catalysts with different sulfur contents. In the dehydrogenation of perhydro benzyltoluenes, the degree of dehydrogenation shows the volcano-shaped dependence on the sulfur content at the maximum with 0.21 wt% sulfur. The best performance catalyst is robust in recycle runs owing to negligible Pt growth and sulfur loss. The sulfur added lowers the electron density of Pt atoms because of the favorable contact between Pt and sulfur species by the SDP method compared to the conventional impregnation. The electron-deficient Pt atoms weaken the adsorption of aromatic products and induce appropriate H 2 adsorption. Thus, the titled catalyst is tolerant to the dehydrogenation products and less selective to the side product methylfluorene. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni(2 +) sites in BEA zeolite are active catalysts for isobutane dehydrogenation. • H 2 site time yield for isobutane conversion increases with Ni loading. • Characterization indicates Ni-alkyl intermediates rather than Ni-hydride. • XAS and QM/MM modeling suggests Ni(2 +) site heterogeneity. • Ni(2 +) in 6 membered-rings (6MR) are more stable, but less active than Ni(2 +) in 5MR. Ni-modified beta zeolite (Ni/BEA) catalysts activate carbon-hydrogen bonds in light alkanes, as demonstrated through isobutane reaction testing. Controlled synthesis of Ni/BEA allows for efficient introduction of ion-exchanged Ni sites at varying Ni loadings (0.43% − 1.8%). These catalysts exhibit site time yields (STY) for H 2 production that increase with increasing Ni loading. A detailed analysis of secondary reactions and carbon deposition based on the relative molar flowrates of product C and H indicates that the observed increase in H 2 STY with increasing Ni loading is likely attributed to both increasing alkane activation activity and increasing formation of hydrogen-deficient aromatic products retained within the catalyst pores. In situ diffuse-reflectance UV–visible-NIR absorbance and X-ray absorption spectroscopies indicate isolated, 4-coordinate Ni(2+) species for all loadings. Quantum mechanics/molecular mechanics modeling identifies two distinct Ni(2+) sites consistent with the structural characterization, but with differing relative stabilities due to their coordination environment. Computed reaction energetics for isobutane dehydrogenation demonstrate that the more stable Ni(2+) species at a six-membered 4Si-2Al ring, Ni-6MR, is less active for isobutane dehydrogenation than the less stable Ni(2+) at the five-membered 3Si-2Al ring, Ni-5MR. The differing local structure of the isolated cationic Ni sites in Ni/BEA offers a possible rationalization for the increased H 2 STY observed at greater Ni loadings. [ABSTRACT FROM AUTHOR]

[Display omitted] • 0.5Pt/Zn@S-1 catalyst exhibits remarkable propane dehydrogenation performance. • Propane dehydrogenation is benefited from the formation of Pt 1 Zn m sites. • The activity-structure relationship is investigated by systematic characterization. The utilization of Pt-based catalysts in the catalytic conversion of propane to propylene (PDH) remains pivotal in industrial processes. However, the scarcity of Pt and its high cost necessitates innovative strategies to enhance Pt dispersion and catalytic performance. In this study, we present an approach involving the in-situ incorporation of Zn cations into Silicalite-1 (S-1) zeolite through one-pot hydrothermal synthesis, which facilitates the anchoring of atomically dispersed Pt atoms. The synthesized 0.5Pt/Zn@S-1 catalyst exhibits the dehydrogenation performance of 25 % propane for approximately 34.2 % propane conversion and 95.1 % propylene selectivity (propylene turnover rate of 14.2 s−1), coupled with robust stability of up to 60 h without distinct deactivation under a WHSV of 49.1 h−1. Comprehensive characterizations reveal the formation of atomically dispersed Pt-Zn catalytic sites. The Pt atoms are incorporated with the Zn cations and dense silanol nests. This unique configuration facilitates a synergistic effect between Pt and Zn for dehydrogenation. [ABSTRACT FROM AUTHOR]

Reaction mechanism network for the catalytic conversion of n-heptane over H-ZSM-5. [Display omitted] • Dehydrocyclization of n-heptane to toluene over H-ZSM-5 zeolite was firstly investigated. • Conversion of n-heptane to toluene via 1-heptene identified as the most favorable cyclization route. • The C1-C5 ring closure of 1-heptene emerges as the most kinetically favorable pathway. • Dehydrogenation steps in the n-heptane conversion are energetically demanding. The dehydrocyclization of naphtha is a process of great significance in the petrochemical industry, as it enables the production of valuable aromatics. While experimental studies have demonstrated the catalytic activity of H-ZSM-5 zeolite in converting alkanes to aromatics, there is a notable absence of theoretical investigations into the reaction mechanisms involved in the dehydrocyclization of naphtha. Herein, the conversion of n-heptane to toluene over H-ZSM-5 zeolite was examined using first-principles density functional theory (DFT) calculations. The dehydrocyclization process of n-heptane involves several key steps, including dehydrogenation, isomerization, and cyclization. Specifically, the dehydrogenation of n-heptane produces 1-heptene, 2-heptene, and 3-heptene, which then undergo various dehydrocyclization pathways leading to the formation of toluene: (i) C1-C5 ring closure of 1-heptene; (ii) C1-C6 ring closure of 1-heptene; (iii) C2-C6 ring closure of 2-heptene; (iv) dehydrogenation of 3-heptene to heptadiene, with C1-C5 ring closure; and (v) dehydrogenation of 3-heptene to heptatriene, with C1-C6 ring closure, followed by sequential ring expansion and/or dehydrogenation to toluene. The DFT results indicate that the dehydrogenation steps are energetically demanding, with the conversion of n-heptane to toluene via 1-heptene identified as the most favorable cyclization route. This theoretical investigation provides valuable insights into the fundamental mechanisms underlying the dehydrocyclization of naphtha for the production of aromatics, with potential implications for the development of more efficient catalytic processes in the petrochemical industry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phosphorus-modified Pt/Al 2 O 3 resists sintering, preserving nanoparticles below 1 nm size. • Optimal P:Pt ratio (1.8) boosts activity by 18 % in perhydro benzyltoluene dehydrogenation. • Activity enhancement persists even after catalyst treatment at 900 °C, crucial for industrial applications. • Effective stabilization achieved through straightforward impregnation and high-temperature treatment. • XPS and XRD confirm Pt remains in reduced state, vital for maintaining dehydrogenation activity. In this study, we demonstrate that phosphorus-modification of Pt/Al 2 O 3 leads to sinter-stable catalysts with improved activity in the dehydrogenation of perhydro benzyltoluene, an attractive liquid organic hydrogen carrier. TEM images show that platinum nanoparticles are stabilized to a size below 1 nm by the P-modification procedure, while unmodified counterparts show considerable sintering after reduction at 600 °C. The modification procedure starts by a simple impregnation of Pt/Al 2 O 3 with H 3 PO 3 , followed by a high temperature treatment above 550 °C. It is crucial to adjust the right P:Pt ratio to reach stabilization of all platinum nanoparticles and thereby high catalytic surface areas. In our dehydrogenation studies, a catalyst with the optimal molar P:Pt ratio of 1.8 shows a 18 % higher activity compared to the unmodified sample. Even after treating the catalyst at temperatures up to 900 °C, this activity boost remains. XPS and XRD measurements prove that Pt stays in its reduced elemental state, also after P-modification, which is essential for a good dehydrogenation activity. The phosphorus species act as an anchor for the Pt particles on the Al 2 O 3 surface, reducing their mobility and preserving small nanoparticles. [ABSTRACT FROM AUTHOR]

The depicted PNN-Mn complex serves as a versatile catalyst for the dehydrogenative oxidation of a wide range of primary alcohols in water to form their corresponding carboxylic acids. [Display omitted] • A green and sustainable process for producing the carboxylic acids in aqueous media. • Manganese-promoted efficiently dehydrogenative oxidation of the alcohols into corresponding carboxylic acids. • The wide range of alcohols including either (hetero)aromatic or aliphatic types. • A possible mechanism regarding the oxidation process proposed through controlled experimentation. Three classes of manganese(I) complex cation, [(PN H N)Mn(CO) 3 ]Br (Mn1), [(SN H N)Mn(CO) 3 ]Br (Mn2) and [(N R N H N)Mn(CO) 3 ]Br (Mn3 (N Me), Mn4 (N Et), Mn5 (N iPr)), all incorporating a chelating 5,6,7,8-tetrahydro-8-quinolinamine (N H N) but distinct in their third donor atom, have been assessed as catalysts for the dehydrogenative oxidation of primary alcohols to form their corresponding carboxylic acids. Using water as solvent and NaOH as base, PN H N-containing Mn1 proved the most effective allowing both aromatic and aliphatic alcohols to be converted at 160 °C with excellent functional group tolerance (25 examples disclosed). A possible mechanism for this process, that makes use of an acceptorless dehydrogenation pathway, has been proposed and supported by targeted experimentation. Overall, these catalysts show great promise for applications in atom-economic carboxylic acid synthesis as well as in the development of organic hydride-based hydrogen storage systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Homogeneous cobalt complex for acceptorless dehydrogenation (AD) and borrowing hydrogen (BH) processes. • Chemoselective formation of alkenylation and alkylation products starting from methyl heteroarenes and alcohols. • Sustainable, efficient, and atom-economic C–C bond formation. • Synthetic derivatization to medicinally important structures. Chemoselective synthesis allows for the generation of diverse products from identical starting materials, which is a significant strategy to build molecular diversity rapidly. By employing acceptorless dehydrogenation and borrowing hydrogen strategies, we herein report a cobalt-catalyzed chemoselective C(sp3)–H bond functionalization of methyl heteroarenes, the alkenylation and alkylation products are obtained using alcohol as the coupling partner under different reaction conditions. The scopes of both arenes and alcohols, synthetic applications, preliminary mechanistic studies, and a proposed mechanism were presented. [ABSTRACT FROM AUTHOR]

One of the most important scientific challenges of the time is to design catalysts that produce H 2 from "minimum CO 2 " sources. One way to do this is by aqueous phase reforming (APR) of sugar alcohol molecules derived from biomass. However, to date, H 2 yields have been disappointing, indicating a need to optimize catalysts and reaction conditions to improve H 2 production. This requires a detailed understanding of the APR mechanism. There are three primary steps: dehydrogenation, decarbonylation, and water gas shift. However, the details of these steps remain unknown due to the large and complex structures of the reactant molecules, the aqueous reaction conditions, and the participation of multiple types of active sites in the mechanism. To begin to address these knowledge gaps, herein we study the effect of liquid H 2 O solvent and multiple types of active sites on the mechanism of CH 3 OH dehydrogenation. Specifically, we use a combination of multiscale modeling, microkinetic modeling, and Fourier transform infrared spectroscopy to determine the mechanism of CH 3 OH dehydrogenation on Pt/Al 2 O 3 catalysts. We investigate sites on the terraces of large Pt particles as well as sites at the Pt/Al 2 O 3 perimeter and the influence of liquid H 2 O on both. We show that the reaction is predominantly carried out on terrace sites due to inhibition by strongly bound H 2 O molecules at perimeter sites. We further show that water plays a significant role in the CH 3 OH dehydrogenation mechanism on Pt terrace sites but that these changes do not influence the observed rate of CH 3 OH consumption. [Display omitted] • The mechanism of methanol dehydrogenation in aqueous phase is explored with multiscale modeling. • Feedback looping between experiments and simulations reveals key mechanistic features. • Water molecules at the metal/support interface prevent methanol adsorption and facilitate hydrogenation. • The active sites are the sites on the Pt terraces. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lower pressure favors deoxygenation, which occurs only at higher temperatures. • Benzene is formed by dehydrogenation of cyclohexane, not by direct deoxygenation. • Demethylation of anisole occurs due to its reactive adsorption on Al 2 O 3. • Methylation of the aromatic ring accompanies demethylation at lower pressure. Anisole is a model molecule for studying hydrodeoxygenation (HDO) of lignin-derived oxygenates. Here we elucidate its HDO pathway over 10 % Ni/Al 2 O 3 catalyst. Adsorption experiments showed that anisole is adsorbed on the acidic sites of the Al 2 O 3. Anisole adsorption at 200–300 °C is reactive in nature, and results in its demethylation. The catalyst was tested at 100–300 °C, 5–40 bar H 2 pressure. Conversion of 78 % was obtained at 5 bar and 300 °C, restricted by hydrogenation-dehydrogenation equilibrium. HDO mainly starts through the ring-hydrogenation pathway. This is followed by demethoxylation beyond 180 °C. At 5–12 bar, cyclohexane dehydrogenates to benzene. This was confirmed by conducting an HDO experiment with methoxycyclohexane. At lower pressure deoxygenation is favored; and demethylation is accompanied with methylation of the aromatic ring, for temperature >260 °C. Investigation of the initial reaction stages showed that anisole HDO on Ni/Al 2 O 3 catalyst proceeds via two independent pathways i.e., reactive adsorption/(de)methylation and aromatic ring hydrogenation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pt@MIL-101(Fe) was prepared via a microwave-assisted self-assembly of MIL-101(Fe) in the presence of PVP-capped Pt colloids. • Efficient mass diffusion and substrate-catalyst interactions imparted by the MOFs over Pt@MIL-101(Fe). • Pt@MIL-101(Fe) shows superior activity for coproduction of benzimidazoles and hydrogen from o-phenylenediamines and alcohols under visible light. • Higher stability over Pt@MIL-101(Fe) is due to the embedding of Pt NPs within MIL-101(Fe). A Pt@MIL-101(Fe) nanocomposite, with Pt nanoparticles (NPs) fully embedded and well dispersed in the matrix of MIL-101(Fe), was prepared via a microwave-assisted self-assembly of MIL-101(Fe) in the presence of PVP-capped Pt colloids (PVP = polyvinylpyrrolidone). The as-obtained Pt@MIL-101(Fe) nanocomposite shows a superior activity for the one-pot reaction between o-phenylenediamines and alcohols to synthesize benzimidazoles under visible light, with concomitant generation of clean energy hydrogen, ascribed to an efficient mass diffusion and substrate-catalyst interactions imparted by the MOFs. The embedding of the Pt NPs within the MIL-101(Fe) contributes to the relatively high stability of Pt@MIL-101(Fe), since the aggregation of the Pt NPs can be significantly inhibited. This study not only provides a green and atom-efficiency strategy for the synthesis of benzimidazoles with concomitant generation of clean hydrogen, but also demonstrates that a rational fabrication of metal NPs/MOFs nanocomposites is important for them to be used as multifunctional catalysts for light initiated one-pot tandem/cascade reactions. [ABSTRACT FROM AUTHOR]

Ultrafine PdCr nanoparticles are immobilized on amine-functionalized titanium carbides. The optimized Pd 0.7 Cr 0.3 /NH 2 -MXene system exhibit an excellent activity toward catalyzing FA dehydrogenation. [Display omitted] • Ultrafine PdCr nanoparticles are immobilized on amine-functionalized titanium carbides. • The optimized Pd 0.7 Cr 0.3 /NH 2 -MXene system exhibit an excellent activity toward catalyzing FA dehydrogenation. • The amine group can significantly improve the kinetics of formic acid decomposition. Heterogeneous catalysis of formic acid dehydrogenation is considered as a promising strategy for safe and efficient hydrogen production and transportation. Herein, we reported the immobilization of the bimetallic PdCr nanoparticles on amine-functionalized titanium carbides (PdCr/NH 2 -MXene). By the amine group, the ultrafine PdCr NPs with the size of 1.8 nm were well dispersed on MXene. The optimized Pd 0.7 Cr 0.3 /NH 2 -MXene system exhibit an excellent activity toward catalyzing FA dehydrogenation, affording the overall turnover frequency (TOF) value of as high as 1906 h−1 at 323 K. Such an excellent catalytic performance is attributed that the introduction of amine group not only benefits the formation of ultrafine and well-dispersed PdCr NPs, but also modulates the electronic structure of metal catalytic sites, resulting in an enhancement for catalyzing FA dehydrogenation. This work may supply a new strategy for development of high-performance bimetallic nanosystem for tremendous catalytic application in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Highly dispersed CrSiβ catalyst is prepared via a two-step post-synthesis method. • The 3CrSiβ catalyst shows the best performance for CO 2 -ODP. • The amount of Cr6+ oxides is responsible for the activity of CrSiβ for CO 2 -ODP. • In-situ formed coordinatively unsaturated Cr3+ oxides are active sites for CO 2 -ODP. • A detailed redox mechanism including the formation of active sites is proposed. Although the supported CrO x is widely applied as an important industrial catalyst for oxidation processes (such as propane dehydrogenation), the molecular-level understanding of its catalytic mechanism is still limited. In this work, the oxidative dehydrogenation of propane with carbon dioxide (CO 2 -ODP) was exploited as a probe reaction to investigate CrO x highly dispersed over dealuminated β zeolite (CrSiβ). It was revealed that the activity of the CrSiβ catalyst was dependent on the dispersion of Cr species and the content of initial highly-dispersed Cr6+ oxides. Namely, the oxygen of terminal Cr = O bonds in initial Cr6+ oxides could rapidly react with propane molecules, thus generating the coordinatively unsaturated Cr3+ oxides as active sites for the redox cycles of CO 2 -ODP. In this redox cycle, the unsaturated Cr3+site takes an oxygen from a CO 2 molecule and then the activated oxygen reacts with propane to produce H 2 O and propene. This finding is not only important for the molecular understanding of the CrO x catalytic properties, but also is beneficial for the rational design of more efficient CrO x catalysts for dehydrogenation reactions including CO 2 -ODP. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ga 2 O 3 nanoparticle catalysts were prepared with different ratios of γ-Ga 2 O 3 and β-Ga 2 O 3. • Treatment of β-Ga 2 O 3 with H 2 (500 °C) generates weak Lewis acid sites (LAS). • Treatment of γ-Ga 2 O 3 with H 2 (500 °C) generates strong LAS. • More weak LAS in β-Ga 2 O 3 -H 2 are due to additional oxygen vacancies on the surface. • More strong LAS in γ-Ga 2 O 3 -H 2 are due to restructuring (densification) of the surface. Three γ/β-Ga 2 O 3 nanoparticle catalysts that differ in the relative ratio of γ-Ga 2 O 3 to β-Ga 2 O 3 were prepared to evaluate the effect of H 2 treatment (500 °C, 2 h) on the coordination environment of bulk and surface Ga sites, Lewis acidity and catalytic activity in propane dehydrogenation (PDH). Independent of the H 2 treatment, the initial PDH activity of the γ/β-Ga 2 O 3 catalysts increases with the fraction of the β-Ga 2 O 3 phase. This is explained by the presence of weak Lewis acid sites (LAS) in β-Ga 2 O 3 while such sites are absent in γ-Ga 2 O 3. Treatment with H 2 increases the catalytic activity of all three γ/β-Ga 2 O 3 catalysts but for different reasons. For catalysts with higher fractions of β-Ga 2 O 3 , H 2 treatment increases further the relative abundance of weak LAS, likely by generating coordinatively unsaturated Ga sites (such as tricoordinated Ga sites nearby oxygen vacancies). In contrast, H 2 treatment of a catalyst containing a predominant fraction of γ-Ga 2 O 3 phase induces disorder in the sub-surface structure of the nanoparticle, that is, it forms gallium and oxygen vacancies in the bulk and favors migration of gallium, and likely also of oxygen, to the surface. This induces a surface reconstruction that notably increases the fraction of strong LAS (and proportionally decreases the fraction of medium LAS), while creating no weak LAS in γ-Ga 2 O 3 -H 2. Therefore, the increase in the catalytic activity of H 2 -treated γ-Ga 2 O 3 is explained by the higher density of surface Ga sites in γ-Ga 2 O 3 -H 2 relative to calcined γ-Ga 2 O 3. H 2 -treated catalysts that contain a higher relative amount of weak LAS also feature a higher relative abundance of gallium hydride species associated with a low frequency FTIR band at ca. 1931–1939 cm−1, that is, weak LAS likely give weakly-bound hydrides in β-Ga 2 O 3. Our results highlight that weak LAS in unsupported Ga 2 O 3 catalysts are more active in PDH than mild or strong LAS. [ABSTRACT FROM AUTHOR]

[Display omitted] • Acceptorless dehydrogenation of primary alcohols to carboxylic acids with pure hydrogen liberation. • Highly efficient and recyclable solid self-supported catalysts with single-sited catalytic centers. • Up to 99% yield and selectivity with broad substrates and sensitive functional group tolerance for both aryl and alkyl alcohols. • Under air atmosphere and at low catalyst loadings. The acceptorless dehydrogenation of diverse aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been accomplished by self-supported NHC-Ru single-site catalysts under mild reaction conditions. Besides broad substrates with excellent activity, selectivity and good tolerance to sensitive functional groups, the solid single-site catalyst could be recovered and reused for more than 20 runs without deactivation. Remarkably, up to 1.8 × 104 turnover numbers could be achieved by this newly developed sustainable protocol in gram scale at low catalyst loading, highlighting its potential in industry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of CO 2 addition to propane dehydrogenation explored for Pt-Sn/MgAl 2 O 4 catalyst. • Pt-Sn/MgAl 2 O 4 catalysts comprehensively characterized by QXAS. • Quantitative determination of Sn composition in Pt-Sn alloy and the alloy phase itself. • Reaction network proposed for CO 2 -assisted propane dehydrogenation. CO 2 -assisted propane dehydrogenation has been studied on Pt-Sn/MgAl 2 O 4 catalysts with support surface area of ~ 127 m2/g or ~ 5 m2/g, 3 wt% Pt and a Pt/Sn molar ratio of 3/1. In situ XAS was employed to track the dynamic changes occurring to the catalyst in presence of a reductive (H 2) or oxidative (CO 2) atmosphere. Reduction leads to the formation of a Pt-Sn alloy, the active compound for propane dehydrogenation. Oxidation by CO 2 led to the loss of the Pt-Sn alloy due to firstly oxidation of Sn to SnO and subsequent oxidation of SnO to SnO 2. The electronic and structural properties of the catalyst were determined by modelling of the EXAFS data. The Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) method was used in conjunction with the XAS data to determine the amount of Sn present in the Pt-Sn alloy phase and the phase of the alloy itself: after a single step reduction 42% of all Sn goes into Pt 3 Sn alloy, participating in the reaction, with the remainder being SnO x. The percentage of Sn going into the Pt 3 Sn alloy increased after 10 H 2 /O 2 redox cycles to 72%. A combination of in-situ XAS with CO 2 -PDH activity data covering CO 2 :C 3 H 8 ratios from 0.25:1 to 1:1 allowed to show that CO 2 helps to improve conversion of propane by means of the reverse water gas shift reaction, wherein the product H 2 generated from PDH reacts with feed CO 2 to shift the equilibrium towards products. The reaction performed better at lower ratios of CO 2 :C 3 H 8. Increasing ratios of CO 2 :C 3 H 8 induced faster deactivation of the catalyst by the oxidation of Sn to SnO x , leading to loss of Pt-Sn alloy. Suppression of carbon accumulation occurred by means of the reverse Boudouard reaction with the carbon formed during PDH. As possible reaction network for the entire CO 2 -PDH reaction, a combination of Langmuir-Hinshelwood (L-H) and the Mars-van Krevelen mechanism (MvK) was proposed. The MvK steps were the oxidation of Sn to SnO by CO 2 , which would then subsequently react with the H 2 and C generated from PDH that takes place on Pt sites by the L-H mechanism, to go back to the Pt 3 Sn alloy. [ABSTRACT FROM AUTHOR]

[Display omitted] • The strong effect of potassium on the performance of the CoY catalyst in the ESR process. • Influence of speciation and localization of potassium on its effect in the CoY catalyst. • Enhanced interaction of cobalt phase with zeolite upon K-doping via IE and IWI routes. • Stronger ethanol adsorption on Co(K)Y prepared via the ion-exchange (IE) route. • Undesired reduction of the cobalt work function in the IWI-prepared K/CoY catalysts. In this work, we offer an understanding of the potassium impact on the performance of the cobalt-zeolite catalysts in the ethanol steam reforming process (ESR) conditions. The catalytic behavior of the undoped and K-doped cobalt-containing materials (10 wt% of cobalt) is discussed concerning their structure and surface properties. The 2K/CoY and 4K/CoY samples, where potassium was introduced on the HY support together with cobalt phase upon incipient wetness impregnation (IWI method), were faced with the Co(K)Y sample with K+ in the ion-exchange positions (IE method), where cobalt was introduced on the surface of KY support by IWI method. The chemical and phase composition, texture, morphology, and reducibility of the catalysts were comprehensively evaluated by the ICP, XRD, low-temperature N 2 adsorption, STEM/EDX, and H 2 -TPR methods, respectively. The catalysts' active sites nature was assessed in the quantitative pyridine and CO adsorption FT-IR studies. A detailed description of the surface properties of the materials was faced with their catalytic interaction with the ethanol–water mixture at 500 °C. The in situ FT-IR reaction studies supported the catalytic results. Undoped CoY catalyst exhibited 100% ethanol conversion, whereas its selectivity to H 2 , CO 2 , CO, and C 2 H 4 , reached values in the range of 55–60%, 25–30%, 0–5%, and 65–70%, respectively, pointing the dehydration path as the main one. The presence of potassium altered the reaction mechanism, what reflected in the decrease of ethanol conversion to 75–80% for Co(K)Y sample and 15–30%, and 5–10%, respectively for 2K/CoY and 4K/CoY samples. Undesired C 2 H 4 production was reduced to 40% for the potassium-exchanged sample and did not occur for both, 2K/CoY and 4K/CoY, IWI-prepared samples. The coke species of various chemical nature were identified over the deactivated catalysts with the use of Raman, UV–VIS, and XPS spectroscopic methods and thermogravimetric analysis method. [ABSTRACT FROM AUTHOR]

[Display omitted] • The development of a crystallization inhibition strategy led to a dense copper phyllosilicate precursor. • Significantly higher oxygen vacancy concentration was found on the surface of the reduced sample Cu/SiO 2 (20 K) than traditional Cu/SiO 2. • Cu/SiO 2 (20 K) showed prominent activity in methanol dehydrogenation coupled with DMO hydrogenation reactions, with a high yield of 85.4% of ethylene glycol (EG) achieved. • DFT calculations were performed to elucidate the intrinsic active site during reaction over Cu/SiO 2 (20 K). The reducibility of heterogeneous Cu-based precursor greatly influences the activity and stability of the final catalysts because the excessive reduction to metallic Cu significantly deactivates the catalysts. Herein, we develop a crystallization inhibition strategy to fabricate the granular and densely stacked copper phyllosilicate precursor which possesses stronger resistance to H 2 reduction. The reduction-resistant CuSiO 3 precursor contains more abundant Cu+ species and oxygen deficiencies, which was verified by O 2 -TPD, TGA, O XPS and Cu XAES measurements, and is beneficial for methanol dehydrogenation and dimethyl oxalate (DMO) adsorption. A high yield of 85.4% of ethylene glycol (EG) was achieved from DMO hydrogenation at 240 °C, with methanol as both the solvent and hydrogen supplier. The delicately designed synthesis of specific Cu precursor with unique properties resulted in an excellent multi-functional Cu catalyst for coupled methanol dehydrogenation and DMO hydrogenation to EG. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Gerischer-Mauerer mechanism is favored under the typical reaction condition for the electro-oxidation of ammonia. • NH 2 + NH 2 coupling to form N 2 H 4 is the main path for N-N bond formation. • The dehydrogenation of NH 3 to NH 2 is the rate-limiting step in the whole process. • Side reactions are observed with explicit solvent molecules present during simulation. Electrochemical ammonia oxidation reaction (AOR) is one of the most effective methods to utilize ammonia. Currently, the favorable coupling process during AOR and most important intermediates are still under debate. Herein we used ab initio molecular dynamics (AIMD) method combined with deliberately designed free-energy calculations to thoroughly study the energetics of elementary steps during AOR. The main pathway of N 2 formation during AOR is initiated by the dehydrogenation of NH 3 to NH 2 , and subsequent NH 2 + NH 2 coupling to form N 2 H 4 , followed by stepwise dehydrogenation of N 2 H 4 to N 2. The Gerischer-Mauerer mechanism was found to be favored in the process. The dehydrogenation of NH 3 to NH 2 was determined to be the rate-limiting step, and NH 2 is the most important intermediate. Through this work, the overall reaction network and corresponding energetics of AOR is revealed, which may enlighten the understanding of AOR and further accelerate corresponding catalyst innovation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effects of heat-treatment atmosphere and temperature for Co/Al 2 O 3 precursor on Co species in Co/Al 2 O 3 are investigated. • Co/Al 2 O 3 -H 2 treated under H 2 atmosphere shows superior catalytic performance for propane dehydrogenation to Co/Al 2 O 3 -O 2 and Co/Al 2 O 3 -Ar. • The enhanced performance of Co/Al 2 O 3 -H 2 is attributed to the presence of tetrahedral Co2+ in CoAl 2 O 4 and its relatively high surface concentration. • Tetrahedral Co2+ and metallic Co in Co/Al 2 O 3 are active; however, the former is more selective, while the latter is more active. Co-based catalysts have attracted increasing attention as promising catalysts for propane dehydrogenation (PDH) because of their C–H bond activation ability. Co species in Co/Al 2 O 3 are present in various forms, such as Co 3 O 4 , CoAl 2 O 4 , CoO, and metallic Co. However, the catalytic properties of the various Co species in PDH are unclear. In this work, we prepare Co/Al 2 O 3 with different compositional distribution of Co species by heat-treating the supported Co precursor under O 2 , Ar, and H 2 atmospheres at temperatures between 500 and 600 °C. H 2 -treated Co/Al 2 O 3 results in superior performance compared to O 2 - and Ar-treated catalysts. This is attributed to the relatively high Co surface concentration and relatively high ratio of tetrahedral Co2+ stabilized in CoAl 2 O 4 to the total Co species. A detailed study shows that both tetrahedral Co2+ and metallic Co in Co/Al 2 O 3 are active for PDH, but the former is more selective. [ABSTRACT FROM AUTHOR]

[Display omitted] • A highly active Pd/NH 2 -CNT catalyst for formic acid dehydrogenation was prepared. • A combination of Cit and APTES enables the formation of ultrasmall Pd particles. • Amine functional groups from APTES capture H+ from HCOOH to increase HCOO– • A regeneration process is required to use the catalyst repeatedly. Formic acid is a promising hydrogen source and liquid organic hydrogen carrier because of its high hydrogen density. To produce hydrogen from formic acid, catalytic dehydrogenation of formic acid over Pd-based catalysts has been investigated. Here, a highly active catalyst is rationally designed. Carbon nanotubes without micropores were adopted as a support to facilitate the mass transport of reactants or products. Pd particles were made as small as possible to provide a large number of active sites and to alleviate the activation barrier for hydrogen desorption. Amine functional groups were introduced into carbon nanotubes to generate formate anions by capturing protons from formic acid. Based on this design, ultrafine Pd nanoparticles (1.76 nm) on amine-functionalized carbon nanotubes were successfully synthesized. This catalyst demonstrated remarkable activity for the formic acid dehydrogenation reaction, with a high turnover frequency value of 2560 h−1 at 30 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] Several reactive characterizations were used to study the effect that reduction duration of PtSn-K/MFI has on hydrocarbon catalysis, including propane dehydrogenation, propane hydrogenolysis, and ethane H/D exchange. Propane dehydrogenation results demonstrate that increased reduction time causes the PtSn-K/MFI to have higher selectivity towards propylene, lower rates of catalyst deactivation, and lower rates of dehydrogenation. Consistent with higher selectivity towards propylene with longer catalyst reduction times, slower rates of hydrogenolysis are also observed over a large range of H 2 :propane ratios. H/D exchange experiments to assess rates of C–H activation were carried out on PtSn-K/MFI by using ethane and D 2 , which demonstrate that longer reduction time significantly inhibits the rate of C–H activation on PtSn-K/MFI. The substantial effects observed by using reactive characterizations were difficult to be interpreted by more advanced characterization techniques such as EXAFS, because the structural changes of the PtSn nanoclusters are quite subtle. Indeed, in a previous report on the PtSn-K/MFI material, Pt and Sn EXAFS were statistically indistinguishable with different reduction times, illustrating that combining reactive characterizations, particularly with the application of H/D exchange, provides the ability to differentiate fundamental effects that impact catalyst performance. The importance of C–H activation was confirmed by isotopic experiments for propane dehydrogenation, which indicate that the first C–H activation step is rate-limiting during dehydrogenation, with a kinetic isotope effect of ∼2.5. These results together show that increased reduction time gives a catalytic material with superior catalytic properties (i.e. higher propylene selectivity and lower deactivation rates), and this is proposed to be due to increased platinum-tin interactions, which modifies and weakens hydrocarbon adsorption, thereby limiting strongly adsorbed intermediates that are precursors to hydrogenolysis products and coke. [ABSTRACT FROM AUTHOR]

Synthesis of silanol nest-containing, siliceous MFI mesoporous zeolites using Na-free synthesis gel was useful for the formation of rare-earth-platinum nanoalloy catalysts, to achieve high performance in propane dehydrogenation. [Display omitted] • Mesoporous MFI zeolites are obtained under sodium-free synthesis conditions. • Sodium-free synthesis is important to form silanol nests on the zeolite surface. • Nanoalloys of Pt and Y are supported on mesoporous MFI zeolites. • Pt-Y alloy nanoparticles are characterized by weak hydrogen chemisorption. • Pt-Y alloy nanoparticles exhibit high performance in propane dehydrogenation. Mesoporous zeolite-supported Pt 3 Y catalyst deactivates slowly in propane dehydrogenation, maintaining high propane conversion and propylene selectivity, but the formation of the intermetallic compound requires atomistic migration of yttrium through silanol nests on the zeolite. Compared to the cumbersome generation of silanols via framework demetallation, we report a direct synthesis of mesoporous MFI zeolite possessing silanol nests. The synthesis procedure employed a diammonium-type bromide surfactant [C 18 H 37 N(CH 3) 2 C 6 H 12 N(CH 3) 2 C 4 H 9 Br 2 ] and a sodium-free silica source. The basicity of the synthesis mixture was adjusted by the addition of readily available N(CH 3) 4 OH, instead of converting the surfactant to hydroxyl form. The presence of silanol nests in the resultant zeolite was confirmed by IR and NMR spectroscopies. When the zeolite was supported with 0.50 wt% Pt and 0.50 wt% Y using nitrate precursors, a remarkably long catalytic lifetime of 20 days was obtained with high propane conversion and propylene selectivity under the reaction condition using neat propane gas at 853 K. [ABSTRACT FROM AUTHOR]

[Display omitted] • CeO 2 with well-defined (1 0 0) and (1 1 1) facets are valuable model metal oxide catalysts to probe acid and base sites. • Morphology of CeO 2 nanoparticles affect the acid site properties regardless of oxygen defect density. • The CeO 2 (1 0 0) facet has stronger base sites leading to increased rates of 2-propanol dehydrogenation to acetone. • The CeO 2 (1 1 1) facet has stronger acid sites along with a higher acid site density which increase the rates of 2-propanol dehydration to propene. CeO 2 nanoshapes, cubes with dominant (1 0 0) facets and octahedra with dominant (1 1 1) facets, were synthesized to investigate the influence of surface structure on acid-base properties. An optimization of calcination temperatures, coupled with Raman and TEM, was employed to minimize the intrinsic (Frenkel-type) defect sites and their potential complications on the facet studies involved in this work. The acid-base properties of these CeO 2 nanoshapes were characterized with in situ pyridine and CO 2 adsorption using infrared spectroscopy and quantified using pyridine, ammonia, and CO 2 temperature-programmed desorption (TPD). The (1 0 0) facet displayed weaker acid sites with lower site density than the (1 1 1) facet which had a similar density of base sites but those on the (1 0 0) facet were stronger. A strong correlation was observed between 2-propanol conversion and each facet's acid-base properties. CeO 2 cubes exhibited greater base-site catalyzed dehydrogenation to acetone while the more acidic CeO 2 octahedra were more active in dehydration to propene. [ABSTRACT FROM AUTHOR]

[Display omitted] • Non-precious intermetallic compound catalysts for propane dehydrogenation. • Scaling relations are established using formation energies over terraces and steps. • Descriptor-based microkinetic analysis is carried out to obtain volcano curves. • Fe 3 Ga 1 is a good catalyst candidate with improved catalytic performance. By using a descriptor-based microkinetic analysis combined with results from density functional theory calculations over eight transition-metal (including Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au) terrace and stepped surfaces, intermetallic compounds have been screened to search for inexpensive and environmentally friendly propane dehydrogenation (PDH) catalysts with enhanced catalytic performance. Based on the scaling relations, the formation energies of ethyl on terrace and methylidyne on stepped surfaces are identified as two descriptors to represent the energetics of other reaction intermediates and transition sates. The derived PDH activity and propylene selectivity volcano curves not only provide a rational interpretation of the previously experimentally reported catalyst candidates, but also predict several unexpected binary combinations by screening 1482 A 3 B 1 and 741 A 1 B 1 intermetallic compounds. The non-precious Fe 3 Ga 1 is then synthesized and evaluated. Its improved propylene selectivity and catalytic stability with respect to those of the Pt catalyst validates the theoretical predictions experimentally. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu surfaces are saturated with bidentate formates (*HCOO*) during catalysis. • *HCOO* species saturate at 0.25 monolayer (0.25 *HCOO* per Cu surface atom). • HCOOH adsorbs molecularly at interstices (□) within the *HCOO* adlayer. • The coexisting HCOOH□ enables *HCOO* to decompose bimolecularly. • Biomolecular decomposition occurs at lower barriers than the unimolecular route. The elementary steps and site requirements in formic acid (HCOOH) dehydrogenation on Cu surfaces remain of keen interest because formate species act as intermediates or spectators in methanol synthesis and water–gas shift reactions. Steady-state and transient kinetic data, isotopic effects, infrared spectra during catalytic and stoichiometric reactions, and theoretical treatments based on density functional theory (DFT) provide evidence for bimolecular reactions, in which saturated bidentate formate (*HCOO*) adlayers, present at 0.25 ML (0.25 *HCOO* per surface Cu atom), react with undissociated species (HCOOH□) bound at interstices within formate adlayers (□) to form H-bonded bimolecular HCOOH□-*HCOO* adducts. The co-existence of vicinal HCOOH□ and *HCOO* moieties is evident from antisymmetric infrared bands for *HCOO* that become stronger as a result of their H-bonding that perturbs the induced dipole moment of *HCOO* upon vibration, consistent with DFT-derived vibrational frequencies and intensities for such perturbed species. The *HCOO* moiety in this complex undergoes C-H activation via a transition state that is preferentially stabilized through H-bonding with the vicinal HCOOH□ relative to its *HCOO* precursor. DFT-derived HCOOH dehydrogenation activation barriers and those determined from the evolution of CO 2 from pre-adsorbed *HCOO* species are about 10 kJ mol−1 smaller in the presence of gaseous HCOOH reactants (because of HCOOH□-*HCOO* interactions) than those for the unimolecular decomposition of bound *HCOO* species. Such bimolecular routes are consistent with measured effects of HCOOH, H 2 , and CO pressures and of H/D isotopic substitution on dehydrogenation turnover rates and represent the predominant channel for the formation of CO 2 and H 2 during catalytic HCOOH dehydrogenation on Cu nanoparticles. A saturated *HCOO* adlayer that retains binding interstices and the presence of HCOOH(g) enable a sequence of elementary steps unavailable for *HCOO* species, thus circumventing unassisted unimolecular routes that exhibit higher activation barriers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Desulfurization networks of 2-phenylcyclohexanethiol under H 2 and Ar were obtained. • Hydrogenolysis and β-elimination were the two main reaction pathways under H 2. • Ni and Co mainly accelerated the β-elimination pathway under H 2. • The two main reaction pathways under Ar were β-elimination and dehydrogenation. • Both pathways under Ar were enhanced by Ni and Co. The desulfurization of 2-phenylcyclohexanethiol (2-PCHT) was studied over sulfided Mo/γ-Al 2 O 3 , Ni-Mo/γ-Al 2 O 3 , and Co-Mo/γ-Al 2 O 3 catalysts under 5.0 MPa H 2 or Ar at 240 °C. Under H 2 , the desulfurization of 2-PCHT proceeded mainly through the hydrogenolysis and β-elimination pathways. The former was faster than the latter over Mo/γ-Al 2 O 3. Ni and Co accelerated the β-elimination pathway but hardly affected the hydrogenolysis pathway. The activity of Mo/γ-Al 2 O 3 was enhanced by Ni, whereas Co did not show any promoting effect. Under Ar, the desulfurization of 2-PCHT occurred mainly through the β-elimination and dehydrogenation pathways. The β-elimination pathway was faster than the dehydrogenation pathway. Both pathways were enhanced by Ni and Co. Ni and Co promoted the dehydrogenation pathway mainly by promoting the dehydrogenation-ring closure reaction. The inhibiting effects of piperidine depended on the reaction and catalyst. Under Ar, Ni-Mo/γ-Al 2 O 3 was more sensitive to piperidine inhibition. [ABSTRACT FROM AUTHOR]

[Display omitted] • Infrared spectra of CO adsorbed on Pt particles with varying size distributions revealed several sites with distinct reactivity. • Larger Pt particles dehydrogenate methanol faster and at lower temperatures than smaller Pt particles with or without co-adsorbed H 2 O. • Even on smaller Pt particles, methanol appears to dehydrogenate on the metal sites of highest coordination first. • Co-adsorbed H 2 O promotes the formation of bridging CO but hinders dehydrogenation on small Pt particles. Dehydrogenation is the first reaction of the aqueous phase reforming (APR) mechanism of polyols, and its rate is likely affected by the environment at the active site. This study focuses on reactions of methanol on benchmark Pt/γ-Al 2 O 3 catalysts probed by infrared spectroscopy under high vacuum. CO in linear and bridging coordination are the dominant surface species on metal sites. Pt particle sizes and reaction temperatures are varied to identify the kinetically preferred active site for methanol dehydrogenation as either lowly coordinated (edges, corners, interface) or highly coordinated (terraces) metal atoms. Interpretation of temperature-dependent IR spectra up to 450 °C show that larger Pt particles produce more CO at lower temperatures from complete methanol dehydrogenation. Similarly, time-resolved isothermal experiments at 150 °C showed equilibrium conversion occurred much faster on larger Pt particles than smaller ones. Features of evolving ν(C≡O) bands (shape, vibrational frequencies, integrals) suggest that, even on small Pt particles, CO first forms on the scarcely available terraces, or possibly in the form of islands. We have thus experimentally identified highly coordinated Pt metal as the more active site in overall methanol dehydrogenation. The electronic and chemical effects of co-adsorbed water and hydrogen on dehydrogenation activity and the CO spectra are discussed. The co-adsorption of water, an abundant APR component needed for the water-gas shift reaction, does not appear to affect methanol dehydrogenation on large Pt particles but hinders the reaction on small Pt particles as evident by limited growth in the respective ν(C≡O) bands. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pd/C catalysts toward HCOOH dehydrogenation were synthesized by cold plasma. • The influence of plasma working gas was investigated. • H 2 discharge is beneficial to the increase of Pd/C atomic ratio. • Pd/C-H 2 P prepared by H 2 cold plasma possessed the highest activity. • The high performance was due to the small Pd nanoparticles and high Pd/C atomic ratio. Cold plasma has been proved to be an efficient method for synthesizing high performance Pd/C catalysts. However, the influence mechanism is still in obscure. In this work, the influence of cold plasma working gas, including air, Ar, O 2 and H 2 , on the structure and performance of the Pd/C catalysts were investigated. Formic acid (HCOOH) dehydrogenation was selected as a probe reaction to investigate the performance of the Pd/C catalysts, and the catalytic activity of the catalysts follows the order: Pd/C-H 2 P > Pd/C-ArP > Pd/C-AirP ≈ Pd/C-O 2 P. The Pd/C-H 2 P catalyst possessed the highest activity, and the TOF initial was as high as 552.4 h−1. The discharge parameters indicated that few micro discharge channels were generated in H 2 plasma, and the power of a single-channel discharge is high. It facilitates the migration of the Pd active species from the pores to the outer surface of the support, and the mean size of the Pd nanoparticles were 2.6 ± 1.0 nm. In addition, the atomic ratio of Pd/C and the content of metallic Pd in Pd/C-H 2 P, determined by XPS, were as high as 0.0229 and 50.8%, respectively. These are beneficial to the reaction, and ensured the highest catalytic activity of the Pd/C-H 2 P catalyst. In contrast, the discharge in Ar plasma was mild and the regulation effect was not as strong as that in H 2 plasma. Therefore, the catalytic activity of Pd/C-ArP was inferior to Pd/C-H 2 P. In addition, since there was a severe ablation of the carbon support and agglomeration of Pd nanoparticles in O 2 plasma and air plasma, both of Pd/C-O 2 P and Pd/C-AirP exhibited poor catalytic activity toward HCOOH dehydrogenation. [ABSTRACT FROM AUTHOR]

Lattice oxygen consumption (H 2 reduction) leads to generating oxygen vacancies and coordinatively unsaturated Co-O acid-base pairs for efficient PDH. Even a trace amount of O 2 can fill the oxygen vacancies quickly and inhibit the activity. [Display omitted] • Co cu -O acid-base pairs from lattice oxygen consumption of CoO x species are the active sites for PDH. • Activity of CoO x /Al 2 O 3 catalysts are significantly inhibited by a trace oxygen. • Oxygen concentration in the C 3 H 8 feed gas is a non-negligible factor in the development of new Co-based PDH catalysts. High temperature and a reducing atmosphere are characteristic of propane dehydrogenation (PDH) reaction. Under such condition, the real surface structure of catalysts often differs from that in the ambient environment, particularly for CoO x species with multiple valence states and coordination. Here, a combination of in situ/operando Raman spectroscopy, in situ UV–Vis diffuse reflectance spectroscopy (DRS), and density functional theory (DFT) calculations reveal that coordinatively unsaturated Co-O (Co cu -O) acid-base pairs via lattice oxygen consumption are the PDH active sites of CoO x /Al 2 O 3 catalysts. This highly dispersed Co cu -O species exhibit a C 3 H 6 formation rate and C 3 H 6 selectivity as high as 2 mmol‧g cat −1‧min−1 and 95 %, respectively, which is comparable to most state-of-the-art CoO x -based catalysts. However, industrial C 3 H 8 raw gases typically contain 10–1000 ppm oxygen gas, and the complete eliminating oxygen increases costs. PDH catalytic performance of CoO x /Al 2 O 3 catalysts is sensitive to the extremely low concentration of oxygen gas and is significantly inhibited by it. The fundamental reason is that the concentration of Co cu active sites is determined by the competitive reaction between the filling of trace oxygen on oxygen vacancies and lattice oxygen consumption. The reaction rate of the former is significantly higher than that of the latter. The higher reducibility of CoO x species leads to relatively weaken inhibition of trace oxygen for PDH activity. The oxygen content in the propane feed gas is a non-negligible factor in the development of new Co-based PDH catalysts, especially for their industrial applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Calcium additives stabilize the catalytic performance of Pt-In alloy nanoparticles in the non-oxidative ethane dehydrogenation reaction. • The first-order deactivation rate constant drops by an order of magnitude when the calcium overcoat is present. • Coke deposited on the catalyst fraction and silica diluent fraction are separately characterized to understand spatial distribution. • Temperature-programmed oxidation and spatially-resolved Raman mapping reveal that the calcium species inhibit crystallization and enhance migration of coke species. Understanding and mitigating catalyst deactivation in high-temperature alkane dehydrogenation reactions is critical toward improving their energy and atom efficiency. In this work, we show that a partial overcoat of calcium oxide on a Pt-In alloy catalyst reduces the rate of catalyst deactivation by 10-fold during the non-oxidative dehydrogenation of ethane to ethylene. During 20 h of time-on-stream at 600 °C in 5 % C 2 H 6 , the Ca-doped PtIn 2 catalyst retains >85 % of its initial activity while the undoped PtIn 2 deactivates to <20 %. Temperature-programmed oxidation and spatially-resolved Raman spectroscopy reveal that the improved catalyst stability stems from enhanced migration of coke precursors away from the catalytically-relevant Pt sites to the silica support. Strikingly, the Ca overcoat does not alter the inherent rate and selectivity of coke formation but rather its crystallinity and localization, which nonetheless has a dramatic impact on the long-term performance of the catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co/ZrO 2 catalysts with single Co2+ are efficient for C 3 H 8 dehydrogenation to C 3 H 6. • 1Co/ZrO 2 performed durable over multiple dehydrogenation/regeneration cycles. • 1Co/ZrO 2 showed higher activity than a commercial analogue of K-CrO x /Al 2 O 3. • The high activity results from a synergy effect between Co2+ and Zr cus. • Recombination of surface H species is the rate-limiting step in C 3 H 6 formation. Due to the increased production of shale gas containing propane, the share of non-oxidative propane dehydrogenation (PDH) in the large-scale production of propene is expected to continue to grow. There are, however, some ecofriendly and cost shortcomings associated with the currently applied Cr- or Pt-containing catalysts. Against this background, we present here Co/ZrO 2 alternatives and reveal the fundamentals affecting their activity, which can be used for purposeful catalyst design. Co2+ species homogeneously distributed within the lattice of ZrO 2 significantly increase the activity of coordinatively unsaturated Zr4+ for the PDH reaction. The increase is caused by accelerating both the cleavage of CH bonds in propane and the recombination of surface H species, with the latter reaction being the rate-limiting step. The best-performing catalyst outperformed an analogue of commercial K-CrO x /Al 2 O 3 in terms of the rate of propene formation and demonstrated durable performance over a series of 10 PDH/regeneration cycles under industrially relevant conditions. It also outperformed most previously developed Co-containing catalysts in terms of propene productivity. The space–time yield of propene formation achieved at 57 % equilibrium propane conversion at 550 °C was 0.71 kg·h−1·kg cat -1. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sub-monolayer Mo oxides are demonstrated as stable alkane dehydrogenation catalysts. • Partially reduced Mo4+ sites are the active species for dehydrogenation. • Catalyst structure is stable under reaction conditions regardless of Mo loading. • Deactivation is due to coke formation, not continual catalyst restructuring. • Mo reduction to oxidation states lower than Mo4+ correlates with increased coking. Potassium-promoted, alumina-supported molybdenum oxide is investigated for non-oxidative isobutane dehydrogenation, with an emphasis on sub-monolayer coverages. After pre-reduction in H 2 , initial isobutene turnover frequencies are largely independent of Mo loading, but deactivation rate constants increase by >100-fold as loadings increase to monolayer, leading to a >13-fold difference in reaction rates at extended time on stream. Mo oxidation state by in situ X-ray absorption spectroscopy is stable with time on stream, arguing against continued catalyst restructuring as the origin of deactivation. Across the set of loadings, isobutane dehydrogenation and coke formation are correlated with partially reduced Mo4+ and deeply reduced Moδ+ sites, respectively. Given the stable dehydrogenation activity of low-loaded Mo, in contrast to the rapid deactivation of high-loaded Mo, sub-monolayer metal oxides may warrant further investigation as light alkane dehydrogenation even when their bulk counterparts may not. [ABSTRACT FROM AUTHOR]

The C 3 H 6 formation rate of γ/δ,-Al 2 O 3 catalyst is in line with the concentration of oxygen vacancies. The coordinatively unsaturated Al-O Lewis acid−base pairs close to oxygen vacancy are responsible for the propane dehydrogenation. [Display omitted] • The surface oxygen vacancy amount of Al 2 O 3 can be controlled by CO reduction. • The r(C 3 H 6) of γ/δ-Al 2 O 3 is in line with the concentration of oxygen vacancies. • The consumption of lattice oxygen forms (Al cus -O) pairs for propane dehydrogenation. • The different Al cus -O pairs tune the adsorption energy and the barriers of key steps. Recently, the coordinatively unsaturated metal-O Lewis acid-base pairs of metal oxides are found to be able to activate the C–H bond of light alkane efficiently. For the inert crystal Al 2 O 3 , we found that the surface oxygen vacancy amount of Al 2 O 3 can be controlled by pretreatment of CO reduction, and the nearby coordinatively unsaturated Al-O (Al cu -O) pairs can effectively catalyze propane dehydrogenation (PDH). The C 3 H 6 formation rate of γ/δ-Al 2 O 3 is in line with the concentration of oxygen vacancies. The experiments and DFT calculations illuminate the importance of oxygen vacancy on the surface of Al 2 O 3 for PDH reaction. The consumption of lattice oxygen reduces the one coordination number of the bonding Al, the formed Al cu -O as defective acid-base pairs, can be an effective way to tune the adsorption energy of the intermediates and the barriers of key steps (the first C H activation and H 2 formation) to enhance the performance of PDH through both site-dependent concerted and stepwise mechanisms. [ABSTRACT FROM AUTHOR]

[Display omitted] • Detailed mechanisms for non-oxidative dehydrogenation of propane were mapped out. • d 2- d 8 transition metals were comparably studied. • C-H activation barrier is correlated with HOMO propane -LUMO catalyst gap. • Lower LUMO catalyst –HOMO propane gap, higher activity of the catalyst. Non-oxidative dehydrogenation of propane is a potential route to produce more valuable chemical feedstock propene. Understanding of the catalytic origin is essential for high performance catalysts design. Herein, the detailed mechanisms for non-oxidative dehydrogenation of propane catalysed by silica supported vanadium are systematically studied to elucidate a possible reaction network, in which the stepwise dissociative C-H bond activation is consistently most favourable. Consequently, stepwise dissociative C-H bond activation is used to investigate the d 2– d 8 transition metal-catalysed non-oxidative dehydrogenation of propane. Frontier orbital analysis reveals that non-oxidative dehydrogenation of propane originates from the interaction between the highest occupied molecular orbital (HOMO) of propane and the lowest unoccupied molecular orbital (LUMO) of the catalysts, indicating that the smaller the gap between the HOMO and LUMO, the higher the reaction activity. Moreover, the largest energy barriers for these reactions correlate with the LUMO catalyst –HOMO propane gap. A lower LUMO catalyst –HOMO propane gap leads to a lower reaction barrier and higher activity of the catalyst. This study provides a new strategy of theoretical catalyst design for non-oxidative propane dehydrogenation by modulating the gap between the HOMO of propane and the LUMO of catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Si additives disperse in a Co–Al 2 O 3 matrix and introduce moderate surface acid sites. • Si additives change the stability of the Co2+––Al 2 O 3 catalyst rather than its initial activity. • Si modification changes the graphitization level and reactivity of formed coke species. • Si modification regulates the adsorption mode, strength, and amount of C 3 H 6 on catalysts. • C 3 H 6 co-feeding changes the coking rate rather than the coke distribution over Co catalysts. The effects of Si-additive modification on nonoxidative propane dehydrogenation (PDH) over γ -Al 2 O 3 sheet-supported isolate Co2+ catalysts have been investigated. Si addition cannot change the nanosheet structure and tetrahedral Co2+ coordination of the Co catalysts; nonetheless, it introduces a number of moderate-strength acid sites by the formation of composite SiAl oxides. Promoted catalytic stability is achieved on Si-modified Si–Co–Al 2 O 3 in comparison with the Si-free Co–Al 2 O 3 catalyst. In spite of similar total content and H/C ratios of deposited coke species on these two spent catalysts, a relatively lower graphitization degree and a higher ratio of highly reactive coke species are observed on the Si–Co–Al 2 O 3 catalyst. Furthermore, the co-feeding of C 3 H 6 significantly changes the coking reaction rates but not the coke distributions on Co-based catalysts. The C 3 H 6 temperature-programmed desorption profiles and in situ diffuse reflectance infrared Fourier transform spectra suggest that the interaction of C 3 H 6 with Co catalysts can be affected by Si modification tuning the coking property and the catalytic stability of Co2+–Al 2 O 3 -based catalysts for the PDH reactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sn-Beta zeolite with Lewis acid sites is able to activate C-H bond. • Sn-Beta zeolite exhibits high performance in propane dehydrogenation. • Theoretical calculation suggest that the propane dehydrogenation occurs on the Lewis acid sites. The gap between supply and demand of propylene has become more and more evident, because of a large consumption of the downstream products derived from propylene. Propane dehydrogenation (PDH) constitutes an important alternative for the production of propylene, and thus considerable attention has been paid to the development of eco-friendly and cost-efficient catalysts for this process. Herein, we discover that the Sn-Beta zeolite with Lewis acid sites can activate the C-H bond, and exhibits high catalytic performance in the PDH. XRD, STEM, and XPS characterizations confirm that Sn species are incorporated into the zeolite framework, and H 2 -TPR suggests that there is a strong interaction between Sn species and zeolite framework. It is found that the Lewis acid is the active site for dehydrogenation reaction, and the Brønsted acid is responsible for cracking reaction. The dehydrogenation rate/cracking rate is positively proportional to the L/B ratio, and a high L/B ratio is beneficial for the propane dehydrogenation reaction. The Na-Sn-Beta-30 catalyst possessing the highest amount of Lewis acid but the lowest Brønsted/Lewis ratio, exhibits the best performance in the PDH, which delivers propane conversion of 40% and propylene selectivity of 92%. Most importantly, these Sn-Beta zeolites are extremely stable without any detectable deactivation under the harsh reaction condition for 72 h. Density functional theory calculations reveal that both Sn and adjacent O atom or OH group cooperatively act as the active sites. The PDH occurs through the direct reaction mechanism in which hydrogen molecule is produced by the direct coupling of H atom of primary C 3 H 7 motif with the Brønsted proton in closed sites or the proton of water in open sites. It seems that open sites are more reactive than the closed ones, and the intrinsic enthalpy barriers are calculated to be 242 ~ 301 kJ/mol depending on the hydroxylation extents. These efficient Sn-Beta zeolites could provide a new possibility for the development of a new generation of PDH catalysts with a high stability for the production of propylene. [ABSTRACT FROM AUTHOR]

• γ-alumina performs a very selective propane dehydrogenation reaction in the presence of H 2 S. • Catalytic activity was enhanced after H 2 S pretreatment. • Active sites upon H 2 S exposure consists of an unmodified AlIII site and new sulfur exchanged site. • S-exchanged sites are more reactive towards C-H scission based on DFT and two-site kinetic model. • O 2 -TPO and XPS indicates the presence of sulfurous coke. A bulk γ-Al 2 O 3 catalyst shows high selectivity for propane dehydrogenation upon pretreatment and co-feeding with H 2 S. The reaction kinetics, deactivation rates, and active sites for propane dehydrogenation on this catalyst were characterized using fixed bed conversion studies, NH 3 -TPD, O 2 -TPO, XPS, and density functional theory (DFT). Specifically, we observe that the selectivity to propylene was 94% at ca. 16% propane conversion at 560 °C for a C 3 H 8 :H 2 :H 2 S ratio of 1.1:1:0.1 on γ-Al 2 O 3. Our results indicate that H 2 S can irreversibly modify the active sites of γ-Al 2 O 3 , postulated to be defect sites on the 110 facet comprised of a tri-coordinated Al atom, such that the modified site was more active and selective towards propylene and less inhibited by co-fed H 2 S. Along with XPS and O 2 -TPO, the dehydrogenation-regeneration experiments suggest the formation of sulfurous coke and strong adsorption of reaction products result in a less active catalyst. This study shows the potential of alumina/metal-sulfide as an earth-abundant and relatively benign class of catalysts for alkane activation, especially in the context of sour natural gas upgrading. [ABSTRACT FROM AUTHOR]

We have examined the effect of copper oxidation state in the continuous gas phase coupled phenylacetylene hydrogenation (to styrene) with benzyl alcohol dehydrogenation (to benzaldehyde) over Cu/CeO 2. Analysis by H 2 -TPR, XPS, XRD and STEM-EDX analyses demonstrates the generation of a range of Cu oxidation states (Cu0 (13–77%), Cu+ (13–74%), Cu2+ (0–55%)). The stepwise formation of styrene and ethylbenzene was promoted in the stand-alone phenylacetylene hydrogenation. An increase in Cu0/Cu+ (from H 2 -TPR and XPS) enhanced H 2 chemisorption and styrene TOF , but with low hydrogen utilisation efficiency. The formation of benzaldehyde and toluene was promoted in the stand-alone dehydrogenation of benzyl alcohol, where benzaldehyde selectivity and TOF correlate with the concentration of Cu0. Full hydrogen utilisation, exclusive benzaldehyde/styrene formation and a (3-fold) greater styrene TOF (to attain 100% yield) was achieved in the coupled process, where hydrogenation/dehydrogenation activity correlates with Cu+/Cu0. This opens new directions for sustainable "hydrogen free" hydrogenations over non -noble Cu catalysts. [ABSTRACT FROM AUTHOR]