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Elevated concentrations of CO2 in the atmosphere pose significant challenges, notably contributing to the greenhouse effect. CO2 as an abundant C1 resource converting into high-value oxazolidinones is a promising avenue for effective carbon fixation. Herein, a highly stable binuclear cerium–organic framework, [Ce2(DCTP)2(DMA)2(OAc)2]n (1), has been successfully designed and synthesized, which maintains the intact three-dimensional framework after immersing in solutions with pH ranging from 1 to 12 and various common solvents for 24 hours, respectively. Explorations on CO2 conversion indicate that compound 1 exhibits remarkable catalytic efficiency in the cycloaddition reaction of CO2 with aziridines to form oxazolidinones under relatively low CO2 pressure. 1 can be easily regenerated five times without a significant decrease in yield. Mechanistic experiments show that the high catalytic activity of 1 is attributed to the stable three-dimensional framework, high Lewis acidity, and ample cerium active sites. Notably, 1 is a rare lanthanide metal–organic framework-based (Ln-MOF-based) catalyst for the cycloaddition of CO2 with aziridines under mild pressure. [ABSTRACT FROM AUTHOR]

Direct catalytic conversion of methane to liquid oxygenates under mild conditions remains a challenge due to high bond energy of symmetric CH4. Isolated Rh atoms were supported on hydrophobic fluorine modified TS-1 (FTS-1). Single-atom Rh on FTS-1 catalyst was characterized with Ac-HAADF/STEM and CO adsorption FTIR. The aerobic selective conversion of methane to oxygenates was carried out in a fixed bed continuous flow reactor upon co-feeding CO and H2O at 423 K under relative low pressure (42.3 kPa CH4, 21.1 kPa CO, 10.6 kPa O2, 0.476 MPa H2O). Hydrophobic Rh/FTS-1 catalyst exhibits higher activity (151.9 molproducts/(molmetalh)) than the activity (36.4 molproducts/(molmetalh)) over hydrophilic Rh-ZSM-5 (Si/Al = 15) under such reaction conditions. Hydrophobicity of different catalysts were compared by water adsorption test. The catalytic activity of F modified TS-1 supported single-atom Rh (Rh/FTS-1) is higher than that of unmodified Rh/TS-1 which is due to its higher Lewis acidity as shown by pyridine adsorption FTIR and NH3-TPD. [ABSTRACT FROM AUTHOR]

This study evaluates the effectiveness of fluidizable VOx/MgO-γAl2O3 catalysts for C4-olefin production via n-butane oxidative dehydrogenation (BODH). Catalysts were prepared via vacuum incipient wetness impregnation and then characterized by employing several techniques such as BET (Brunauer–Emmett–Teller) method, XRD (X-ray diffraction), LRS (laser Raman spectroscopy), XPS (X-ray photoelectron spectroscopy), TPR/TPO (temperature-programmed reduction/temperature-programmed oxidation), NH3-TPD (temperature-programmed desorption), NH3 -desorption kinetics and pyridine-FTIR. The BET analysis showed the prepared catalysts' mesoporous structure and high surface areas. The XRD, LRS and XPS established the desirable presence of amorphous VOx phases. The TPR/TPO analyses corroborated catalyst stability over repeated reduction and oxidation cycles. The NH3-TPD and NH3 desorption kinetics showed that the catalysts had dominant moderate acidities and weak metal-support interactions. In addition, Pyridine-FTIR showed the critical influence of Lewis acidity. The VOx/MgO-γAl2O3 catalysts were evaluated for BODH using a fluidized CREC Riser Simulator, operated under gas-phase oxygen-free conditions, at 5 to 20 s reaction times, and at 450 °C to 600 °C temperatures. The developed VOx/MgO-γAl2O3 catalysts demonstrated performance stability throughout multiple injections of butane feed. Catalyst regeneration was also conducted after six consecutive BODH runs, and the coke formed was measured using TOC (Total Organic Carbon). Regarding the various BODH catalyst prepared, the 5 wt% V-doped MgO-γAl2O3 yielded in a fluidized CREC Riser Simulator the highest selectivity for C4-olefins, ranging from 82% to 86%, alongside a butane conversion rate of 24% to 27%, at 500 °C and at a 10 s reaction time. [ABSTRACT FROM AUTHOR]

The indirect conversion of CO 2 into glycerol carbonate using DMC was investigated using pristine sodium titanate nanotubes (NaTNT) and nanostructured titanates (calcined NaTNT at different temperatures) as catalysts. The calcination changes the morphology of the nanostructured titanates, between 200 and 400 °C the nanotubes shape is retained, however above these temperatures (500 and 600 °C) nanoribbons were identified, as well as nanorods obtained at 700 °C. A significant decrease in specific surface area and total pore size in temperatures up 500 °C was also observed. Furthermore, a decrease in the Ti+4/Ti+2 ratio and in the binding energy of Ti 2p3/2 and Ti 2p1/2 were observed, indicating an increase in the electron density and consequently increase in the Lewis acidity character of the titanium atom. All the nanostructured titanates showed good catalytic activity with glycerol conversion and GC selectivity above 90%. The results of the recycling showed that the nanostructured catalysts retained a good catalytic activity with high glycerol conversion (> 90%) although the GC selectivity decreased due the formation of glycidol, a high value-added by-product. [Display omitted] • Titanate nanostructures were synthesized and characterized. • The calcination generated titanate nanorods with distance of 0.8 nm between sheets. • The catalytic tests showed high glycerol conversion, GC yield and GC selectivity. • The improve in the catalytic activity is related to the increase of Lewis acidity. [ABSTRACT FROM AUTHOR]

Understanding the chemistry underpinning intermetallic synergy and the discovery of generally applicable structure-performances relationships are major challenges in catalysis. Additionally, high-performance catalysts using earth-abundant, non-toxic and inexpensive elements must be prioritised. Here, a series of heterodinuclear catalysts of the form Co(III)M(I/II), where M(I/II) = Na(I), K(I), Ca(II), Sr(II), Ba(II) are evaluated for three different polymerizations, by assessment of rate constants, turn over frequencies, polymer selectivity and control. This allows for comparisons of performances both within and between catalysts containing Group I and II metals for CO2/propene oxide ring-opening copolymerization (ROCOP), propene oxide/phthalic anhydride ROCOP and lactide ring-opening polymerization (ROP). The data reveal new structure-performance correlations that apply across all the different polymerizations: catalysts featuring s-block metals of lower Lewis acidity show higher rates and selectivity. The epoxide/heterocumulene ROCOPs both show exponential activity increases (vs. Lewis acidity, measured by the pKa of [M(OH2)m]n+), whilst the lactide ROP activity and CO2/epoxide selectivity show linear increases. Such clear structure-activity/selectivity correlations are very unusual, yet are fully rationalised by the polymerization mechanisms and the chemistry of the catalytic intermediates. The general applicability across three different polymerizations is significant for future exploitation of catalytic synergy and provides a framework to improve other catalysts. Understanding the intermetallic synergy and the structure-performances relationships of catalysts remains challenging. Here, the authors demonstrate a relationship between both the rates, selectivity and the s-block metal acidity in a series of heterodinuclear catalysts based on Co(III) in combination with alkali and alkaline earth metals for three different polymerization reactios. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis of bimetal–organic frameworks (BMOFs) with both Brønsted and Lewis acidities, in which phosphotungstic acid (PTA) was encapsulated in BMOFs. It is efficient in converting starch to 5-hydroxymethyl-furfural (HMF) in deep eutectic solvents (DESs) such as choline chloride and formic acid. The highest yield of HMF (37.94%) was obtained using P0.5/BMOFs1.0 to catalyze starch in a mixed solvent system comprising DESs and ethyl acetate (EAC) (v/v; 2:3) at 180 °C and a reaction time of 10 min. Employing a DES as a cocatalyst and solvent reduced the use of organic solvents. The catalyst showed adequate reusability, and the HMF yield only decreased by 2.88% after six cycles of reuse compared with that of the initial catalyst. This study demonstrates the application potential of BMOFs in the conversion of biomass to useful molecules with commercial and/or research value. [ABSTRACT FROM AUTHOR]

Performance enhancement of metallocene‐based olefin polymerization catalysts can be obtained, among others, by the chemical modification of their support. We investigated a titanated SiO2 (Ti/SiO2) as an improved support material for zirconocene catalysts, which lead to ∼35 % higher ethylene polymerization yields when compared to the unmodified SiO2‐supported metallocene. The improved catalytic performance of the modified catalyst was found to be related to the presence of a Ti‐based active site, second to the Zirconocene centers, as well as to a higher Lewis acidity in the titanated supported‐MAO, which improved the activation of the Zr‐based centers. The Ti active species were generated by reduction of the Ti/SiO2 support with the methylaluminoxane (MAO) co‐catalysts, which introduced oxygen vacancies (VO) and Ti3+ species, as confirmed by probe molecule Fourier Transform Infrared (FT‐IR) spectroscopy and UV‐Vis Diffuse Reflectance Spectroscopy (DRS). The higher Lewis acidity was linked to 5‐coordinated Ti4+, as detected by probe molecules FT‐IR spectroscopy. [ABSTRACT FROM AUTHOR]

Five different ZnO nanocrystallites (ZnO‐1 to ZnO‐5) were successfully synthesized by a surfactant‐assisted hydrothermal technique using various surfactants. All the ZnO nanocrystallites are thoroughly characterized by XRD, IR, UV‐DRS spectroscopy and FESEM‐EDS analysis. Among the synthesized ZnO nanocrystallites, the CTAB‐assisted synthesized ZnO‐4 exhibited a fine disc‐like morphology with a minimum crystallite size (23 nm). Subsequent to reaction optimization studies, the ZnO‐4 is utilized as an efficient catalyst for one pot‐three component green synthesis of 3‐[(aryl)(arylthio)methyl]‐1H‐indoles (4a–4p) via. condensation of a variety of indoles, aromatic aldehydes and aromatic thiols at room temperature in water. The single‐crystal X‐ray structure of 3‐[(phenyl)(phenylthio)methyl]‐1H‐indole (4a) is also been reported (CCDC 2170437). The Lewis acidic property of the catalyst‐supported probable mechanism is well proposed subsequent to pyridine‐IR studies of the ZnO catalysts. Indeed, CTAB‐assisted synthesized ZnO‐4 was found to be most effective and selective Lewis acid catalyst for the synthesis of a variety of 3‐[(aryl)(arylthio)methyl]‐1H‐indole derivatives in water at ambient temperature with merits like higher yields, lower reaction time, catalyst recovery and reuse. [ABSTRACT FROM AUTHOR]

Many complexes based on group 13 elements have been successfully applied as catalysts for the synthesis of cyclic carbonates from epoxides and CO2 and to date these have provided some of the most active catalysts developed. It is notable that most reports have focused on the use of aluminium-based compounds likely because of the well-established Lewis acidity of this element and its cost. In comparison, relatively little attention has been paid to the development of catalysts based on the heavier group 13 elements, despite their known Lewis acidic properties. This study describes the synthesis of aluminium, gallium and indium compounds supported by a readily prepared salphen ligand and explores both their comparative structures and also their potential as catalysts for the synthesis of cyclic carbonates. In addition, the halide ligand which forms a key part of the compound has been systematically varied and the effect of this change on the structure and catalytic activity is also discussed. It is demonstrated that the indium compounds are actually, and unexpectedly, the most active for cyclic carbonate synthesis, despite their lower Lewis acidity when compared to their aluminium congeners. The experimental observations from this work are fully supported by a Density Functional Theory (DFT) study, which provides important insights into the reasons as to why the indium catalyst with bromide, [InBr(salphen)], is most active. [ABSTRACT FROM AUTHOR]

A metal‐free 1,4‐allylation of azadienes with allyltrimethylsilanes catalyzed by B(C6F5)3 has been developed. The high Lewis acidity, good thermal stability, and good hydrolytic stability of the catalyst make this reaction efficient and operationally simple. In contrast to the previously reported 1,2‐allylation of α,β‐unsaturated imines, the 1,4‐allylation of azadienes is described here for the first time. Benzofuran‐, indene‐, dihydronaphthalene‐, chromene‐, and benzothiophene‐based allyl arylmethanes have been obtained in up to 95 % yield. [ABSTRACT FROM AUTHOR]

The valorization of low‐grade industrial residues into valuable materials has been a way to reduce the impact of the industry on planetary boundaries. Silicon‐rich wastes have been used for zeolite synthesis while the impurities originating from wastes have a vital role in the physicochemical properties and the catalytic performance of waste‐derived zeolites. Here, the effect of steaming and the impact of impurities on waste‐derived zeolites were investigated. Steamed waste‐derived zeolite ZSM‐5 maintained their structure while their Brønsted acidity was decreased significantly due to dealumination. Electron paramagnetic resonance revealed that steaming of the samples resulted in the re‐dispersion of Fe impurities phases. The waste‐derived zeolites exhibited a high amount of weak and intermediate acidity upon steaming. Interestingly, the waste‐derived sample with a higher amount of impurities had an increase in Lewis acidity upon steaming, while catalytic testing in the Methanol‐to‐Hydrocarbons reaction exhibited 10 % higher conversion and 4 % in propylene yield. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metathesis is a commercially successful process for the production of lower olefins. • An increase of the F content on support leads to significant increase of the propylene conversion. • The change in the support acidity doesn't affect the structure of surface molybdenum forms. • Olefin metathesis can proceed under mild conditions on modified catalysts. • The strength of OH groups and Lewis acidity are the determining factors for propylene metathesis. Supported MoO 3 /Al 2 O 3 -F catalysts were synthesized and characterized by Raman, IR, and NMR spectroscopy. It was shown that support fluorination leads to partial substitution of surface OH groups with F which is accompanied by increases the strength of both LAS (Lewis Acid Sites) and residual bridging OH groups. But the change in the acidity doesn't affect the structure of surface molybdenum forms. An increase of the fluorine content on γ-Al 2 O 3 up to 6 wt% leads to 4.7-fold increase of the propylene conversion in metathesis reaction (WHSV = 11 h−1, T = 100 °C, p = 9 atm.) with selectivity above 95 %. The results prove that the support acidity plays an important role in the propylene metathesis. The catalyst modification method proposed here opens new opportunities for the improvement of classical metathesis catalysts. [ABSTRACT FROM AUTHOR]

The 2 wt.% of Zn and Ag (Zn1‐x‐Agx; x=0.2, 0.4, 0.6 %) modified SSZ‐13 (SZ‐13) zeolite was prepared by wet‐impregnation method, and its catalytic activity was demonstrated for methanol‐to‐olefin (MTO). The Zn0.6‐Ag0.4/SZ‐13 catalyst exhibited high catalytic activity due to change in properties of catalyst. The Zn particles were highly dispersed inside the SZ‐13; while Ag particles were dispersed on the surface of SZ‐13, confirmed by HRTEM and surface area. The small % of Ag over SZ‐13 promotes ethylene production via aromatization of reaction, and highly dispersed Zn on SZ‐13 help to produce stable ethylene and propylene. The Zn0.6‐Ag0.4/SZ‐13 catalyst showed (∼10 %) higher light olefin (87 %) selectivity than parent SZ‐13 as well as mono metal incorporated SZ‐13. The higher catalytic activity was attributed due to effect of both metals (Zn and Ag), where Ag promotes partial aromatization on the surface, and Zn increases the Lewis acidity in the zeolite pore. This catalyst can help to improve the selectivity of light olefin using MTO reaction. [ABSTRACT FROM AUTHOR]

Post‐functionalization of porphyrinoid catalysts provides a powerful tool for fine‐tuning their electronic structure. We have succeeded in the stepwise methylation of the peripheral nitrogen atoms in ruthenium and cobalt 5,15‐diazaporphyrins. The axial coordination of an anion to the metal center accelerates the second methylation through charge neutralization. N‐Methylation of the diazaporphyrin complexes effectively controls their electron deficiency, Lewis acidity, and catalytic activity. [ABSTRACT FROM AUTHOR]

Polyoxometalates (POMs) as efficient catalysts can be used a wide range of chemical transformations due to their tunable Brønsted/Lewis-acidity and redox properties. Herein, we reported two hybrid and heterogeneous lacunary Keggin catalysts: (TBA)7[PW11O39] (TBA-PW11) and (TBA)8[SiW11O39]·4H2O (TBA-SiW11) (TBA+: tetrabutylammonium) in which [XW11O39]n− anions were coated by TBA+ cations. In this form, TBA+ can easily trap reactants on the surface of the catalysts and increase the catalytic reaction. Therefore, the catalytic performance of both POMs was tested in cyanosilylation of numerous compounds bearing-carbonyl group and trimethylsilyl cyanide under solvent-free conditions. TBA-PW11 is more effective than TBA-SiW11, conceivably due to the higher Lewis acidity of the P than the Si center and to the higher accessibility of the metal centers in the framework structure. Noteworthy, the recyclability and heterogeneity of both POMs catalysts were also examined, and the results confirmed that they remain active at least after three recycling procedures. [ABSTRACT FROM AUTHOR]

A W4C2 cluster was used to model a W2C catalyst with the armchair model of activated carbon support, noted as W4C2/AC. Over W4C2/AC, the mechanism for the hydrogenation of both −H2OH and −CHO groups in 5‐hydroxymethylfurfural (HMF) was theoretically studied in tetrahydrofuran at GGA‐PBE/DNP level. 5‐Methylfurfural was the major product from only hydrodehydration of the −CH2OH group, whereas 2,5‐dihydroxymethylfuran was the minor product from the hydrogenation of both −CH2OH and −CHO groups. The rate‐determining steps were concerned with the −C(H)2−H bond formation for the hydrodehydration of −CH2OH group, and the −(OH)(H)−H bond formation for the hydrogenation of −CHO group. Kinetically, W‐sites promoted the hydrodehydration of −CH2OH group and inhibited the hydrogenation of −CHO group. This stemmed from the strong Lewis acidity of W‐sites, which easily accepted the lone‐pair electrons of the oxygen atom in the −C(OH)(H)− group, making −C(OH)(H)−H bond formation hard, and hampering the hydrogenation of the −CHO group. [ABSTRACT FROM AUTHOR]

Currently, low intimacy between hydrogenation sites and acidic sites causes unsatisfactory catalytic activity and selectivity for the synthesis of 2,5‐hexanedione from C6 furan aldehydes (5‐methylfurfural, 5‐hydroxymethylfurfural). Herein, iodine(I) modification of Pd‐supported catalysts (such as PdI/Al2O3 and PdI/SiO2) was investigated to modulate the hydrogenation sites and acidic sites. Unlike Pd catalysts that produced 71.4 % yield of 2‐hydroxymethyl‐5‐methyl tetrahydrofuran via an overhydrogenation route of 5‐methylfurfural, PdI catalysts showed a high efficiency for 2,5‐hexanedione with 93.7 % yield by a hydrogenative ring‐opening route. More importantly, the selective synthesis of 2,5‐hexanedione from 5‐hydroxymethylfurfural with a high yield of 50.2 % by the hydrogenolysis and subsequent ring‐opening route was reported for the first time. I‐modified Pd nanoparticles produced in‐situ hydrogen spillover, which promoted the selective C=O hydrogenation and ring‐opening steps by regulating the adsorption configuration of the reactants and the transformation of Lewis to Brønsted acidity, respectively. [ABSTRACT FROM AUTHOR]

An active and stable Co catalyst decorated by N species was developed and applied in the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). The catalyst was first synthesized by grafting glucose (G) and melamine (M) on cobalt phyllosilicate (CoPS) hydrothermally, and then by pyrolyzing GM/CoPS at a designated temperature for the carbothermal reduction (denoting as GM@CoPS-X; X = temperature). Among tested catalysts, GM@CoPS-700 showed the most promising GVL productivity (1684 mmol GVL/gsurface Co /h), stability, and recyclability (an ca. 8% loss of initial activity) in five consecutive trials. Doped N species were found to improve the concentration of Coδ+ (0 < δ < 2) with a strong Lewis acidity. The synergy of Coδ+ and Co0 was the key in enhancing the activity of Co-based catalysts derived from CoPS. [ABSTRACT FROM AUTHOR]

The reaction activity of CuFeO 2 as Fenton-like catalyst ways suffered from the low H 2 O 2 utilization efficiency. For this issue, CuFeO 2 @ZnO with core-shell structure was prepared via the hydrothermal method. The optimal catalyst CuFeO 2 @ZnO(20:4) exhibited a 2.6-fold higher H 2 O 2 utilization efficiency compared with the pristine CuFeO 2. Consequently, the degradation activity towards sulfathiazole correspondingly increased by 4.7 times. Meanwhile, the degradation rates of tetracycline and ciprofloxacin were up to 100 % and 84.13 %, which showed the universality of degradation. Combined with the results of ICP-MS, it can be seen that the core-shell structure can effectively immobilize reactive metal ions and inhibit their leaching. The TPD-NH 3 , phosphate capture experiments and DFT calculations demonstrated that ZnO could increase the Lewis acidity on the surface of CuFeO 2 , promote the adsorption of H 2 O 2 , and enhance the transport rate between H 2 O 2 and CuFeO 2 to significantly improve the utilization of H 2 O 2. Lewis acid promotes Fe(III)/Fe(II) cycling as shown by XPS and impedance. Based on the synergistic effect of promoting H 2 O 2 adsorption and Fe species recycling. Significantly enhanced Fenton-like degradation activity of CuFeO 2 @ZnO(20:4). This study provides a new perspective to improve the degradation activity of CuFeO 2 -based catalysts. [Display omitted] • ZnO was ultilized to elevate the Lewis acidity of CuFeO 2. • Lewis acid significantly promotes H 2 O 2 adsorption and Fe(III)/Fe(II) cycling. • H 2 O 2 utilization increased to 63.85 %, a 2.6-fold improvement. • The degradation activity towards sulfathiazole was enhanced by 4.7 times. • The core-shell structure inhibits metal leaching. [ABSTRACT FROM AUTHOR]

Furfural is a renewable lignocellulose-derived platform molecule, which can be transformed into biofuels and value-added chemicals (e.g., furfuryl alcohol and 2-methylfuran over metal-supported catalysts). Despite a number of approaches proposed for designing hydrogenation catalysts, highly selective furfural hydrogenation towards furfuryl alcohol (FA) or 2-methylfuran (2-MF) is still challenging. Here, we report on selective transformation of furfural either to FA or 2-MF achieved over zeolite BEA-supported Rh catalysts by optimizing Si/Al ratio and charge-balancing cations of the support. Among studied H- and Na-exchanged aluminosilicate BEA zeolite supports (Si/Al = 12.5; 25; 68; 150), Rh@Na-BEA catalysts lacking Brønsted and strong Lewis acidity showed enhanced selectivity towards FA (75 – 94% depending on the Si/Al ratio) at 74 – 84% conversion of furfural. In turn, selective formation of 2-MF (98% selectivity at 87% conversion) was observed over Al-rich Rh@H-BEA catalyst (Si/Al=12.5) with the highest concentration of Brønsted acid sites. Weaker adsorption of FA on Na- vs. H-form of Rh@BEA-12.5 catalyst was verified by FTIR spectroscopy and is assumed a key factor governing selective hydrogenation of furfural to FA over Rh@Na-BEA catalysts. [Display omitted] • Selective reduction of C O bond in furfural over Rh@BEA catalysts. • Tailoring acidity of a zeolite support for selective production of FA or 2-MF. • Weaker adsorption of FA on Na- vs. H-form of Rh@BEA catalysts. [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] • Extra-framework aluminum species are introduced in zeolite Y by facile ion-exchange. • Infrared spectroscopy of adsorbed pyridine quantifies the Lewis acid sites. • Introduced Lewis acidic aluminum are charge-neutral species. • The newly introduced Lewis acidity correlates quantitatively to extra-framework aluminum species. Lewis acidity was introduced into zeolite Y (Si/Al = 30) by a facile ion-exchange of aluminum cations followed by calcination. X-ray diffraction and nitrogen physisorption suggest that the zeolitic framework is retained after these treatments. With an increase in the total extra-framework aluminum in the modified zeolites, there was a pronounced increase in the number of Lewis acid sites, as illustrated by FTIR spectroscopy of adsorbed pyridine and carbon monoxide, whereas no significant change in the number of Brønsted acid sites was observed. Likewise, the catalytic activity, i.e. the conversion and rate of reaction for the MPV reduction of 4- tert butyl cyclohexanone using isopropanol over zeolite catalysts, improved considerably after ion-exchange. A quantitative agreement was observed between the concentration of these introduced extra-framework aluminum species with the total Lewis acid content from pyridine-FTIR and with the initial catalytic rates. This illustrates that the newly introduced aluminum Lewis acidic species adopt an octahedral coordination under the conditions of NMR measurement and are responsible for enhanced Lewis acid catalytic activity of the aluminum exchanged zeolites. The preservation of Brønsted acid sites further endorses the charge neutrality of these extra-framework aluminum complexes. [ABSTRACT FROM AUTHOR]

Determining the roles of surface functionality of heterogeneous acid catalysts is important for many industrial catalysts. In this study, the decisive structure of metal−organic frameworks (MOFs) is utilized to identify important features for the effective conversion of d‐xylose into lactic acid. Several acidic MOFs are tested and the combination of Lewis acidity and adjacent hydroxy sites is found to be critical to attain high lactic acid yields. This hypothesis is corroborated experimentally by modification of the MOF to increase such sites, which affords an enhanced lactic acid yield of 79 %, and investigation of the acidity by using in situ FTIR spectroscopy. Density functional theory calculations disclose the cooperative behavior of Lewis acid sites and hydroxy groups in promoting the Cannizzaro reaction, a key step in the production of lactic acid. [ABSTRACT FROM AUTHOR]

• Low-dimensional multi-oxides nanosheet were synthesized successfully by one-step synthesis. • Co-Mn-SnO 2 solid solution promoted the efficient electron interaction for catalysis. • Increased adsorbed oxygen, Mn3++Mn4+, Sn4+ and more acidity on Lewis acid sites were obtained. • E-R and l -H mechanisms co-existed on Co-Mn-SnO 2 surface in SCR reaction process. • L-NH 3 species and bidntate nitrate were the main active species at high temperatures. NH 3 -SCR performances were explored to the relationship between structure morphology and physio-chemical properties over low-dimensional ternary Mn-based catalysts prepared by one-step synthesis method. Due to its strong oxidation performance, Sn-MnOx was prone to side reactions between NO, NH 3 and O 2 , resulting in the generation of more NO 2 and N 2 O, here most of N 2 O was driven from the non-selective oxidation of NH 3 , while a small part generated from the side reaction between NH 3 and NO 2. Co or Ni doping into Sn-MnOx as solid solution components obviously stronged the electronic interaction for actively mobilization and weakened the oxidation performance for signally reducing the selective tendency of side reactions to N 2 O. The optimal modification resulted in improving the surface area and enhancing the strong interaction between polyvalent cations in Co/Ni-Mn-SnO 2 to provide more surface adsorbed oxygen, active sites of Mn3+ and Mn4+, high-content Sn4+ and plentiful Lewis-acidity for more active intermediates, which significantly broadened the activity window of Sn-MnOx, improved the N 2 selectivity by inhibiting N 2 O formation, and also contributed to an acceptable resistances to water and sulfur. At low reaction temperatures, the SCR reactions over three catalysts mainly obeyed the typical Elye-rideal (E-R) routs via the reactions of adsorbed l -NH x (x = 3, 2, 1) and B-NH 4 + with the gaseous NO to generate N 2 but also N 2 O by-products. Except for the above basic E-R reactions, as increasing the reaction temperature, the main adsorbed NO x -species were bidentate nitrates that were also active in the Langmuir-Hinshelwood reactions with adsorbed l -NH x species over Co/Ni modified Mn-SnO 2 catalyst. Probable surface SCR reaction pathways over Ni/Co-modified Mn-SnO 2 were put forward to follow the basic Elye-Rideal reactions between gaseous NO with adsorbed l -NH x on Lewis acid sites at low temperature while also obey the Langmuir-Hinshelwood routes of main active bidentate nitrates with l -NHx as increasing the reaction temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

CF4, one of the Perfluorocompounds (PFCs), also known as a greenhouse gas with high global warming potential. In this study, Zr/γ-Al2O3 catalysts were developed for CF4 decomposition. The addition of Zr onto γ-Al2O3 achieves a high CF4 conversion efficiency of 85% at 650 °C and maintain its activity for more than 60 h, which is obviously higher than that of bare γ-Al2O3 (50%). The mechanism involved in CF4 decomposition over the Zr/γ-Al2O3 are clarified that the surface Lewis acidity sites are the main active center for CF4 directly adsorbing and decomposing. The results of NH3-TPD and FT-IR analyses suggest that the amount of Lewis acidity sites on catalyst surface increases significantly after the introduction of Zr, thereby enhancing the activity of catalyst for CF4 decomposition. The results of XPS analyses confirms the electrons transfer from Zr to Al, which contribute to the increase in Lewis acidity sites. The results of this work will help the development of more effective catalysts for CF4 decomposition. [ABSTRACT FROM AUTHOR]

Bifunctional catalysts on the basis of Ukrainian natural mordenite-clinoptilolite rocks modified by hydrochloric acid and by witness impregnation with nickel have been synthesized. Samples have been characterized by means of XRD, XRF, FTIR-spectroscopy, low temperature nitrogen adsorption/desorption, DTA/TG, TEM. Catalysts have been tested in micro pulse linear hexane isomerization. Hydrochloric acid treatment of natural zeolite rock leads to silica-to-alumina ratio increasing and raising the BET surface as well as the volumes of mesopores and micropores. The nickel nanoparticles deposited over zeolite crystals have a predominant size of 10 nm, but for some samples smaller ones of 5 nm and bigger ones of 20–50 nm have been found using TEM investigations. Pyridine sorption shows Brønsted and Lewis acidity of the catalysts, moreover the lower hydrochloric acid concentration using leads to practically equal Brønsted and Lewis acidity, the higher acid concentrations causes the Lewis acidity predominance. DTA/TG investigations show that water physically sorbed in the pores of the samples has been removed up to 200 °C from lager cavities of acid-treated catalysts and up to 500 °C from narrower cavities for untreated initial rock. Removing zeolite structure water up to 800 °C causes the dehydroxylation and Brønsted acidity transformation into Lewis acidity. The sample dealuminated by 1 mol dm−3 acid with nickel nanoparticles of 5–8 nm demonstrates the best performance in the isomerization of n-hexane. It is characterized by a 20% yield of hexane isomers at 250 °C and 70% selectivity. [ABSTRACT FROM AUTHOR]

The catalytic cross‐coupling of chlorosilanes has recently emerged as an efficient method for the synthesis of organic silicon compounds. Direct Si−Cl bond activation by transition metals is a key elementary reaction in these methods. This theoretical study aimed to elucidate the mechanism of activation of the strong Si−Cl bond in Pd‐catalyzed coupling reaction to gain insights for rational catalyst design. Our results suggest two plausible pathways for the bond activation: (i) trans‐oxidative addition and (ii) SN2‐type oxidative addition assisted by a Lewis acid. With an increase in Cl substituents of chlorosilanes, trans‐oxidative addition highly feasible due to their higher Lewis acidities, in which the facile formation of the Pd→Si interaction enables the smooth activation of the Si−Cl bond. The general mechanism of direct Si−Cl bond activation presented here may prove useful for the rational design of catalysis in the future. [ABSTRACT FROM AUTHOR]

A number of Ce–La–Fe/γ-Al 2 O 3 catalysts were prepared by impregnation and microwave hydrothermal heating based on the ratio of Ce, La, and Fe in natural bastnäsite to examine the synergistic relationship between Ce, La, and Fe in natural bastnäsite and its effects on ammonia selective catalytic reduction (NH 3 -SCR). The results demonstrated that an increase in Fe species is beneficial to the denitration performance of catalysts with a Ce:La:Fe mole ratio of 1:0.6:0.12, thus providing high NO conversion (>95%) at 350 °C. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy results confirmed the formation of a solid solution between Ce, La, and Fe in the catalysts. The BET isotherms and NH 3 -TPD demonstrated that the addition of Fe increased the surface area and strengthened the surface acidity of Lewis acid sites. XPS and in situ DRIFTS indicated that electron transfer occurred between Fe3+/Fe2+ and Ce4+/Ce3+ redox cycles in the catalyst, thereby improving the adsorption and activation ability of NO and NH 3. NO species were adsorbed on the catalysts in the form of monodentate nitrate, and then monodentate nitrate was oxidized to bidentate nitrate. The SCR reaction route was the coexistence of Eley–Rideal and Langmuir–Hinshelwood mechanisms. • Ce–La–Fe/γ-Al 2 O 3 catalysts were synthesized by the microwave hydrothermal method. • The Ce–La–Fe/γ-Al 2 O 3 catalysts showed that solid solution of Ce–La–Fe–O were formed. • The addition of iron can strengthen the surface acidity of Brønsted and Lewis acid sites. • The SCR reaction mechanism followed the Eley-Rideal and Langmuir-Hinshelwood mechanism. [ABSTRACT FROM AUTHOR]

Epoxidation of alkenes is one of the most explored reactions in organic synthesis because of the accessibilities of diverse important compounds from epoxides. Several transition-metal catalysts, in combination with oxidizing agents, have been successfully utilized to achieve alkene epoxides. In this context, methyltrioxorhenium (MTO)-catalyzed epoxidation of alkenes in accordance with different oxidants has been widely reconnoitred where the Lewis acidity of rhenium (Re) is diminished by different Lewis bases to suppress the decomposition of epoxides to diols. Although great success has been accomplished, no review article on MTO-catalyzed epoxidation has been published to date. Therefore, all the advancements in methyltrioxorhenium (MTO)-catalyzed epoxidation of alkenes using different oxidizing agents (aq. H2O2, urea-H2O2, and sodium percarbonate) have been summarized in this comprehensive review article for the scientific community. [ABSTRACT FROM AUTHOR]

[Display omitted] • In-situ FTIR reveals the evolution of surface species during methane activation over NiO/Ce0.83Zr0.17O2. • Adsorbed surface oxygen reacts with activated methyl species to produce formate and carbonate intermediates. • Less reactive oxygen species associated with NiO form alkoxy intermediates with increased selectivity. • Aromatic species cover active Lewis acid sites impeding their activity for methane activation. • Opportunities for improving the selectivity towards alkoxy intermediates are identified. Methane activation over NiO/Ce 0.82 Zr 0.18 O 2 catalysts synthesized by combustion synthesis is studied by in-situ IR spectroscopy and correlated to the properties and oxygen speciation of the catalyst. Through XRD, H 2 -TPR, and pyridine adsorption followed by FTIR spectroscopy, the reducibility and Lewis acidity of the catalysts are assessed. In-situ FTIR spectroscopy is used to monitor the methane activation on catalyst surfaces. Complex IR features of methane-derived surface species are observed and are attributed to the formation of surface alkyl/alkoxy, aldehyde, formate/carbonate, and aromatic species. A data analysis algorithm is developed to evaluate the evolution of different surface species over time. The formation of formate and carbonate species is driven by adsorbed surface oxygen, while less reactive oxygen species associated with NiO allow for the production of aromatics and alkoxy intermediates. By tuning the reducibility and Lewis acidity of the catalyst, the selectivity to alkoxy intermediates can be improved. [ABSTRACT FROM AUTHOR]

A B(dan) moiety (dan=naphthalene‐1,8‐diaminato) of diminished boron‐Lewis acidity has efficiently been installed into organic frameworks by three‐component carboboration of alkenes under copper catalysis, where a Cu−B(dan) species, generated by chemoselective σ‐bond metathesis between a copper catalyst and an unsymmetrical diboron [(pin)B−B(dan)], acts as a key intermediate. The Cu−B(dan) species has also turned out to serve as a B(dan) nucleophile to afford various dan‐substituted organoboranes via borylative substitution of carbon electrophiles. Furthermore, borylation reactions with another Lewis acidity‐diminished boron unit, B(aam) (aam=anthranilamidato), have become feasible by use of (pin)B−B(aam) or H−B(aam). The resulting dan/aam‐substituted organoboranes have been demonstrated to undergo direct cross‐coupling without prior acidic deprotection, regardless of their diminished boron‐Lewis acidity. Synthesis of diverse organostannanes based upon copper‐catalyzed carbostannylation and borylstannylation, in which Lewis acidity increment of a tin center facilitates the progress in some cases, have also been described. [ABSTRACT FROM AUTHOR]

• Pure TiOF 2 is facilely and safely synthesized by solution combustion synthesis. • Strong dependence of crystal phase to calcination temperature. • TiOF 2 exhibits excellent activity (53%) for dehydrofluorination reaction. • The introduction of F element can enhance the Lewis acidity. Hydrofluorocarbons (HFCs) are potent greenhouse gasses with high global warming potential and the emission of which is strictly regulated by Kigali amendment. In this paper, titanium oxyfluoride (TiOF 2) was firstly synthesized by simple solution combustion synthesis in the absence of highly corrosive HF, among which calcination played an important role on the phase of the products. When the precursor was calcinated at 450 °C, pure TiOF 2 could be obtained. The pyrolysis of HFCs results showed that the 1,1-difluoroethane (HFC-152a) conversion over TiOF 2 is about 53%, superior than TiO 2 (40%) due to the enhanced Lewis acidity. Even compared with traditional metal fluoride catalysts (AlF 3 and MgF 2), TiOF 2 held higher stability within 35 h, contributing to the suitable Lewis acidic sites. The formation mechanism of the Lewis acidity was systematically investigated: on one hand, F species made the binding energy of Ti spesies shift to high regions to enhance the Lewis acid strength of Ti species; on the other hand, more oxygen vacancies were generated by the introduction of F, which could act as the Lewis acid sites as well. Hence, this study provides a promising and potential candidate for the catalytic pyrolysis of HFCs. [Display omitted] [ABSTRACT FROM AUTHOR]

The synthesis of a variety of bis(catecholato)germanes is reported. The Lewis acidity of the bis(catecholato)germanes was assessed using the experimental Gutmann–Beckett method and computational FIA and GEI methods. The oligomerization of alkenes using bis(catecholato)germanes demonstrates the use of these complexes in catalysis. The use of donor additives in the dimerization of α-methylstyrene resulted in selectivity control comparable to transition metal catalyst systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Semi-amorphous mixed metal oxides are tunable supports for molecular catalysts. • Productivity of catalysts bound by ion-pairing, can be increased fourfold. • Zinc content of the metal oxide support influences productivity. • Productivity can be related to the concentration of Lewis acid sites on the support. • Lewis acidic iron based metal oxide shows same productivity enhancement. The performance profile of a supported metallocene catalyst in slurry-phase ethylene polymerisation can be significantly enhanced by tuning the chemical composition of the support. By employing catalyst supports derived from zinc-containing layered double hydroxides (LDHs), the slurry phase ethylene polymerisation productivity of (EBI)ZrCl 2 (EBI = rac -ethylenebis(indenyl)) can be quadrupled relative to a magnesium-containing support. Productivity increases approximately linearly with zinc content of the LDH before reaching a plateau; our experiments suggest the productivity of this catalyst system is related to the overall Lewis acidity of the support surface. We have found that iron-containing LDH supports with a similar overall Lewis acidity also result in productivity enhancements, demonstrating the general nature of this phenomena. [ABSTRACT FROM AUTHOR]

Bis‐NHC stabilized germyliumylidenes [RGe(NHC)2]+ are typically Lewis basic (LB) in nature, owing to their lone pair and coordination of two NHCs to the vacant p‐orbitals of the germanium center. However, they can also show Lewis acidity (LA) via Ge−CNHC σ* orbital. Utilizing this unique electronic feature, we report the first example of bis‐NHC‐stabilized germyliumylidene [MesTerGe(NHC)2]Cl (1), (MesTer=2,6‐(2,4,6‐Me3C6H2)2C6H3; NHC= IMe4=1,3,4,5‐tetramethylimidazol‐2‐ylidene) catalyzed reduction of CO2 with amines and arylsilane, which proceeds via its Lewis basic nature. In contrast, the Lewis acid nature of 1 is utilized in the catalyzed hydroboration and cyanosilylation of carbonyls, thus highlighting the versatile ambiphilic nature of bis‐NHC stabilized germyliumylidenes. [ABSTRACT FROM AUTHOR]

Chemical fixation of CO2 as C1 source at ambient temperature and low pressure is an energy‐saving way to make use of the green‐house gas, but it still remains a challenge since efficient catalyst with high catalytic active sites is required. Here, a novel monoclinic azo‐functionalized Zr‐based metal−organic polyhedron (Zr‐AZDA) has been prepared and applied in CO2 fixation with epoxides. The inherent azo groups not only endow Zr‐AZDA with good solubilization, but also act as basic sites to enrich CO2 showing efficient synergistic catalysis as confirmed by TPD‐CO2 analysis. XPS results demonstrate that the Zr active sites in Zr‐AZDA possess suitable Lewis acidity, which satisfies both substrates activation and products desorption. DFT calculation indicates the energy barrier of the rate‐determining step in CO2 cycloaddition could be reduced remarkably (by ca. 60.9 %) in the presence of Zr‐AZDA, which may rationalize the mild and efficient reaction condition employed (80 °C and 1 atm of CO2). The work provides an effective multi‐functional cooperative method for improvement of CO2 cycloaddition. [ABSTRACT FROM AUTHOR]

Description: The α-2Mo1Sn catalyst formed solid solution structure with oligomeric MoO 3 in SnO 2 lattices, which possessed strong Sn-Mo interaction and catalyzed the HDO of guaiacol into phenol with full conversion and 92.5% phenol yield. [Display omitted] • A novel hybrid Mo-Sn oxide catalyst for effective HDO of lignin derivatives into monophenols is proposed for the first time. • The α-2Mo1Sn catalyst formed solution structure with oligomeric MoO 3 in SnO 2 lattices. • The α-2Mo1Sn achieved 92.5% yield of phenol in HDO of guaiacol, higher than that of the previously reported catalysts. • Comprehensive characterizations and catalytic measurements were conducted to figure out the catalysis mechanism. Novel Mo-Sn bimetallic oxide catalysts with highly dispersed oligomeric MoO 3 in SnO 2 lattices, which were synthesized by the co-precipitation method and pretreated by anhydrous ethanol, were first employed in the hydrodeoxygenation of various lignin derivatives to produce monophenols with high activity and selectivity. In comparison with the pure α-MoO 3 and the previous reported catalysts, the α-2Mo1Sn exhibited superior activity in the hydrodeoxygenation of guaiacol, with full conversion and 92.5% phenol yield at 300 °C under 4 MPa initial H 2 pressure in n-hexane for 4 h. According to comprehensive characterizations and catalytic measurements, the excellent performance of α-2Mo1Sn was ascribed to the formation of abundant Sn-O-Mo-O V interfacial sites, which possessed strong Mo-Sn interaction with enhanced surface area, electron-donating group binding ability, Lewis acidity, and redox ability. It was demonstrated that over the present α-2Mo1Sn catalyst system, the Sn-O-Mo-O V interfacial sites could greatly facilitate the adsorption and activation of C aromatic -OCH 3 and C aromatic -CH 3 bonds, and thus significantly promote the demethoxylation and demethylation reaction to produce phenol. This work figures out the rational design of MoO 3 -based catalyst and displays a clear potential for the selective hydrodeoxygenation of lignin derivatives into monophenols. [ABSTRACT FROM AUTHOR]

Halogen bonding, the non‐covalent interaction of Lewis bases with an electron‐deficient region of halogen substituents, received increased attention recently. Consequently, the design and evaluation of numerous halogen‐containing species as halogen bond donors have been subject to intense research. More recently, organoiodine compounds at the iodine(III) state have been receiving growing attention in the field. Due to their electronic and structural properties, they provide access to unique binding modes. For this reason, our groups have been involved in the development of such compounds, in the quantification of their halogen bonding strength (through the evaluation of their Lewis acidities), as well as in the evaluation of their activities as catalysts in several model reactions. This account will describe these contributions. [ABSTRACT FROM AUTHOR]

Transition-metal silicates are recognized as effective solid acid catalysts to produce value-added compounds from bio-based platform chemicals. One crucial feature in such catalytic transformations is the isomorphic substitution of transition metal into the tetrahedral coordination environment of SiO 2 matrices. This substitution generates the acidic sites which represent the catalytically active sites. Herein, the preparation of hafnium-doped mesoporous SiO 2 (hafnosilicates) is disclosed, and these materials are explored as catalysts for the efficient conversion of dihydroxyacetone (DHA) to ethyl lactate (EL). The one-step catalyst preparation is based on the aerosol-assisted sol-gel (AASG) process and leads to spherical mesoporous silicates with a homogeneous insertion of isolated Hf – as single sites into the SiO 2 matrix, as indicated by XPS. These sites display high Lewis acidity (as evidenced by Pyridine-IR) and this translates into good catalytic performance. Moreover, pH adjustment via the controlled addition of triethanolamine before the aerosol process is shown as a practical way to improve the textural properties, the degree of Hf insertion into the SiO 2 matrix (Lewis acidity), and therefore the catalytic activity. Under optimized reaction conditions (5 mL of 0.4 M DHA, 140 °C, 6 h, 200 mg of catalyst), complete conversion of DHA to EL was observed with a yield higher than 45%. [Display omitted] • Mesoporous hafnosilicate catalysts prepared in one step via an aerosol-assisted sol-gel process. • pH adjustment strategy greatly enhanced the degree of Hf insertion resulting in higher Lewis acidity. • Ethyl lactate yield was greatly improved by the amount of Lewis acidity in the hafnosilicates. • Hafnosilicates can be reused in several cycles with high stability and no leaching of active sites. [ABSTRACT FROM AUTHOR]

Nanocarbon-based frustrated Lewis pair (FLP) bifunctional catalysts, on account of their unquenched electron transfer property, are becoming increasingly attractive as catalysts for the CO2 reduction reaction via the dissociative chemisorption of H2. In the present study, we propose a nanocarbon-based FLP catalyst. The pair comprises nitrogen doped/phosphorus doped graphene as Lewis bases and M(C6F5)3 (M = B, Al, Ga, and In) as Lewis acids. The computational investigation reveals that the carbon atoms adjacent to the doped N and P atoms are the active sites towards the dissociative chemisorption of hydrogen molecule. The analyses of the Bader charges and difference charge densities validate the dissociative chemisorption of H2 molecule and the fact that a significant electron redistribution promotes the polarization of the hydrogen molecule. Density of states confirms the hybridization between the p-states of the nitrogen/phosphorus atom and the s-state of hydrogen atom in all FLPs. The dissociative chemisorption of hydrogen is noted in all FLP complexes, thereby facilitating a low barrier reaction path for CO2 reduction. Between P-doped and N-doped FLPs, N-doped FLP catalysts prove to be a more promising counterpart with considerably low activation barriers, ranging between 0.01 and 0.11 eV, towards CO2 reduction. Thus, the present study demonstrates the great potential of doped carbon-based FLPs as novel nanostructure catalysts for CO2 reduction via the direct utilization of molecular hydrogen. [ABSTRACT FROM AUTHOR]

CH3OH formation rates in CO2 hydrogenation on Cu‐based catalysts sensitively depend on the nature of the support and the presence of promoters. In this context, Cu nanoparticles supported on tailored supports (highly dispersed M on SiO2; M=Ti, Zr, Hf, Nb, Ta) were prepared via surface organometallic chemistry, and their catalytic performance was systematically investigated for CO2 hydrogenation to CH3OH. The presence of Lewis acid sites enhances CH3OH formation rate, likely originating from stabilization of formate and methoxy surface intermediates at the periphery of Cu nanoparticles, as evidenced by metrics of Lewis acid strength and detection of surface intermediates. The stabilization of surface intermediates depends on the strength of Lewis acid M sites, described by pyridine adsorption enthalpies and 13C chemical shifts of ‐OCH3 coordinated to M; these chemical shifts are demonstrated here to be a molecular descriptor for Lewis acid strength and reactivity in CO2 hydrogenation. [ABSTRACT FROM AUTHOR]

Cr-based catalysts are widely used in dehydrogenation reactions. In this study, it was aimed to investigate the effects of Cr content on catalyst structure, chromate type and amount. First, the catalyst support MCM-41 was synthesized hydrothermally, and then xCr@MCM-41 (x: 4,6,8,10) catalysts in different mass % ratios were prepared by the impregnation technique. The active monochromates for the reaction was obtained on 4Cr@MCM-41 catalyst at the highest amount. It was shown that Cr metal homogeneously distributed in this catalyst structure. Catalytic tests (600°C, atmospheric) were carried out on the 4Cr@ MCM-41 catalyst selected for its proper crystal size, homogeneous metal distribution and high amount of active monochromate content. As a result of the catalytic tests, high isobutane conversions (80%) were obtained up to the 60th minute and high isobutene selectivity (95%) after the 40th minute. The observed high conversions were explained by the transformation of Cr(II)O2-2, formed by tetrahedrally coordinated Cr(VI)O4-2 structures in the catalyst, into active Cr(III)O3-3 species by using the water in the support structure. After the reaction, it was shown that only <0.1% carbon deposition was detected in the catalyst and the catalyst deactivation was caused by the Cr form change. It was determined that the crystallite size increased (40%) after the reaction, depending on the conversion of Cr+6 to Cr+3. It was also shown that this form change enabled the catalyst surface acidity to be reduced, especially Lewis acid sites, thus increasing isobutene selectivity and preventing coke formation. For xCr@MCM-41 catalysts synthesized by impregnation technique, a 4%Cr content by mass appears to be an appropriate ratio for high isobutene selectivity and high amount of monochromate formation. [ABSTRACT FROM AUTHOR]

Catalytic CO2 conversion is considered to be a promising way to simultaneously reduce greenhouse gas emission and realize carbon resource recycling. Several typical reactions including hydrogenation, carboxylation, carboxylic cyclization, and cycloaddition have been extensively studied for yielding high value‐added products. During the process of CO2 conversion, the introduction of light energy and electricity will dramatically lower the energy consumption for CO2 activation so that the whole reaction can efficiently take place at room temperature and atmospheric pressure. For traditional chemical, photochemical, and electrochemical conversions, the processes can be effectively promoted by the rational engineering of active sites on the catalysts. Herein, the most recent advances on the active site engineering of catalysts involving metal or alloy sites, Lewis sites, defect sites, and elemental doping sites are focused on. The influencing mechanisms on the CO2 activation and selective conversion are further discussed according to the structural properties and the interactions with different active sites. Finally, a brief perspective on the future opportunities and challenges in this field is also presented. Researchers who attempt to explore more efficient catalysts for CO2 activation and selective conversion will be guided. [ABSTRACT FROM AUTHOR]

A series of eight Mn(III)–porphyrin (MnP) complexes with electron-withdrawing substituents at the meso and/or β-pyrrole positions of the macrocycle was designed to uncover electronic and structural aspects of MnP catalytic activity in the cycloaddition of CO2 with epoxides. The complexes, when combined with tetrabutylammonium halides, were active catalysts producing the respective cyclic carbonate under mild conditions. The non-β-brominated complex H3[MnT4CPP] served as a structural framework for the design of a series of homologous complexes, leading to the synthesis of the new β-brominated catalysts H3[Mn(BrxT4CPP)] (x = 2, 4, or 6). The β-brominated catalyst series allowed the investigation of the influence of structural effects versus electronic effects on the catalytic system, demonstrating a good correlation between the catalytic activity and the number of bromine substituents at the β-pyrrole positions. The non-planar distortions of the macrocycle and the consequent steric hindrance are determinant for the reaction outcome. The decrease in catalytic activity despite the increase in Lewis acidity of the metal center highlighted the effect of the out-of-plane distortion on the catalytic activity of manganese porphyrins. [ABSTRACT FROM AUTHOR]

The efficient utilization of biomass, the only globally available, renewable and abundant carbon-neutral source, is of high significance in green and sustainable chemistry. Polyoxometalates (POMs) and POM-based composites have been widely applied in green catalytic reactions, due to their tunable Brønsted/Lewis-acidity and redox properties enabling high reactivity in a wide range of chemical transformations. This review covers recent advances in the chemocatalytic conversion of biomass into chemicals and fuels over POMs and POM–metal composites. For biomass valorisation over POMs, the advances of acid catalysis including hydrolysis, dehydration, etherification, alcoholysis, transesterification and esterification are summarised. Furthermore, applications in chemical oxidation for the synthesis of organic acids and furan chemicals are discussed. For biomass valorisation over metal–POM composites, an overview of tandem reactions (e.g. hydrolysis–hydrogenation, hydrolysis–oxidation, and hydrogenolysis–hydrodeoxygenation) is highlighted. The future prospects of biomass valorisation over POM-based catalysts are finally presented. [ABSTRACT FROM AUTHOR]

• The Fe spin state of Fe(II)Cl 2 (tpm) has been studied by experimental and theoretical investigation. • Theoretical investigation are performed on XAS at the Fe L 2,3 -edges and N K-edge. • The best agreement has been obtained for a low-spin, diamagnetic ground state. • The stability depends upon the ligands, the bulk solvent and the interaction of the vacant site. • Both tpm→Fe(II) σ bonding and a tpm⟵Fe(II) Charge Transfer characterize the Fe–tpm interaction. The Fe(II) spin state in the condensed phase of [Fe(II)Cl2(tpm)] (tpm = [tris(pyrazol-1-yl)methane]; 1) catalyst has been determined through a combined experimental and theoretical investigation of X-Ray Absorption Spectroscopy (XAS) at the FeL 2,3 -edges and NK-edge. Results indicated that in this phase a mixed singlet/triplet state is plausible. These results have been compared with the already know Fe singlet spin state of the same complex in water solution. A detailed analysis of the electronic structure and bonding mechanism of the catalyst showed that the preference for the low-spin diamagnetic ground state, strongly depends upon the ligands, the bulk solvent and the interaction of the complex's vacant site (the sixth) with a further ligand. Moreover, comparison of the electronic properties of the complex in condensed phase and water solution showed an increased Lewis acidity of the catalyst in solution phase, due to a decreasing of the LUMO energy of about 8 kcal/mol. These results gave an overall picture of the electronic behavior of the complex investigated, on going from condensed to water solution phase, explaining the preferred use of 1 as catalyst in homogeneous catalysis. The N Fe(II) interaction has been thoroughly investigated by means of DFT Kohn-Sham and EDA bond analysis applied to i) the isolated [Fe(II)Cl 2 (tpm)] and ii) the [Fe(II)Cl 2 (tpm)] interacting with water as a solvent within the Conductor-like Screening Mode (COSMO) framework. Results showed that both tpm→Fe(II) σ and tpm⟵Fe(II) π Charge Transfer (CT) interactions characterize the Fe(II)–tpm interaction. Moreover, the three tpm N atoms do not equally interact with the Fe(II) and one of them shares a suitable available iron-based d virtual orbital, to bind a further ligand in trans position. [ABSTRACT FROM AUTHOR]

A non-noble metal-based bifunctional Fe–Ni/MMT nanocomposites exhibit excellent H 2 generation capability from the methanolysis of NaBH 4 at a rate of 16,200 mL min−1 g−1 Fe – Ni with 10%Fe–Ni loading on MMT support. Moreover, the evolved H 2 from this catalytic process is efficiently utilized for the one-pot step-wise synthesis of secondary amines from nitrobenzene and aldehydes using NaBH 4 as a source of hydrogen at room temperature. Circumventing the reduction of aldehyde and triggering the formation of imine intermediate through sequential addition of reactants in a time dependent manner has resulted in the excellent yields for aliphatic, aromatic and heterocyclic amines (91–98%). The catalytic activity of Fe–Ni/MMT nanocomposite is ascribed to synergic association of Fe–Ni NPs, Lewis and Brønsted acidity as well as adsorptive nature of MMT. Thus, a simple, facile and greener route is developed for the synthesis of secondary amines with an efficient H 2 generation non-noble metal catalyst and easily accessible H-donor at room temperature. A simple, facile and cost-effective methodology is developed for efficient H 2 evolution and one-pot synthesis of secondary amines from nitrobenzene and aldehyde with non-noble metalbased Fe–Ni/MMT catalyst using NaBH 4 at room temperature. Image 1 • Fe-Ni/MMT exhibit excellent H 2 generation rate of 16,200 mL min−1g−1 Fe–Ni at RT. • Substantially lower energy of activation for the methanolysis of NBH 4. • One-pot cascade synthesis of secondary amines from nitrobenzene and aldehyde. • Reduction, condensation and further reduction occurs in a time-dependent manner. • Simple and cost-effective methodology with non-noble metal catalyst. [ABSTRACT FROM AUTHOR]

For the first time the catalytic activity of AgNdSiW11, was examined in two named reactions, namely Hantzsch and Biginelli reactions. A simple, eco-friendly and highly efficient one-pot synthesis of polyhydroquinoline derivatives via Hantzsch multicomponent reactions (MCRs) involving cyclocondensation of differently-substituted aldehydes, β-ketoesters or dimedone, active methylene compounds, and ammonium acetate as a source of nitrogen, in the presence of AgNdSiW11 as a catalyst in EtOH/H2O under reflux conditions in high yields was successfully achieved. Furthermore, the catalytic performance of AgNdSiW11 was also successfully tested in the synthesis of 3,4-dihydropyrimidin-2-(1H)-ones via Biginelli MCR involving cyclocondensation of differently-substituted aldehydes, ethyl acetoacetate and urea as source of nitrogen in the presence of AgNdSiW11 under reflux conditions in EtOH/H2O. This prolific combination of Ln and POMs inaugurates a powerful class of catalysts for the different chemical transformations, which overcomes key limitations of previously established salts and Lewis acidic metals-based catalysts under low catalyst loading, the use of water scavengers, dry solvents and additives for facilitating the specialized experimental setups commonly employed to the organic reactions. [ABSTRACT FROM AUTHOR]

Ga-modified zeolites represent the most effective catalyst for catalytic transformation of light alkanes to aromatics. GaO+ ions and GaOx clusters on Ga/ZSM-5 zeolites are probed by solid-state NMR. These two types of Ga species show strong Lewis acidity and are quantitatively correlated with the catalytic activity of Ga/ZSM-5 for methane C–H bond activation. The interaction between the surface Ga species and zeolite is characterized by using double-resonance solid-state NMR spectroscopy, which provides direct spectroscopic evidence for the location and distribution of active Ga species. These results provide new insight into the understanding of the nature and role of Ga species in Ga-modified zeolites for the conversion of light alkanes. [ABSTRACT FROM AUTHOR]