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• Oxidation catalyst developed: gold nanoparticles dispersed on Cu-doped spinel MgCr 2 O 4. • Highly active and selective catalysts for gas-phase oxidation of cyclohexanol. • Au Cu synergy due to O 2 activation on Cu species, Au catalyzes C H bond activation. • Au Cu alloy formed during catalytic operation. • >99% cyclohexanol conversion and >90% cyclohexanone selectivity obtained. The industrial production of cyclohexanone from cyclohexanol would benefit from a selective oxidation catalyst. Herein, Cu doping of MgCr 2 O 4 supports for gold nanoparticles active in gas-phase oxidation of cyclohexanol was investigated. Mg 1-x Cu x Cr 2 O 4 exhibited spinel structures (x ≤ 0.25: MgCr 2 O 4 ; x = 1: CuCr 2 O 4) onto which 3–4 nm gold nanoparticles could be dispersed. Cu doping led to higher activity. During reaction, surface Cu2+ was reduced to Cu0, resulting in Au Cu alloy formation. At low temperature, low-Cu-content catalysts (x ≤ 0.1) showed higher activity than high-Cu-content catalysts, likely because the Au Cu alloy with highly diluted Cu was more active for the dehydrogenation step of cyclohexanol. However, Au/Mg 0.99 Cu 0.01 Cr 2 O 4 and Au/Mg 0.9 Cu 0.1 Cr 2 O 4 showed lower cyclohexanol conversion at high temperature than samples with high Cu content, because O 2 activation involving Cu becomes rate-limiting. Stable cyclohexanol conversion and cyclohexanone selectivity were 99.1% and 90.2% (space-time yield of 266 g Ketone g Au −1 h−1) for Au/Mg 0.25 Cu 0.75 Cr 2 O 4 at 300 °C. [ABSTRACT FROM AUTHOR]

Abstract Highly dispersed gold nanoparticles supported on Cu-doped spinel oxides were prepared by a simple deposition-precipitation method. The results indicate that Au/MgCuCr 2 O 4 catalyst is very efficient for gas-phase oxidation of cyclohexanol to cyclohexanone, giving 69.5% and 86.4% yield of cyclohexanone at 260 °C and 300 °C, respectively. Deactivation was not observed in a 100 h stability test. This excellent performance can be correlated with the highly stable gold nanoparticles in the reaction deriving from the strong gold-support interaction and efficient Au Cu synergy. Graphical abstract Unlabelled Image Highlights • First report of gas-phase oxidation cyclohexanol using spinel-supported gold • >95% conversion and > 90% selectivity to cyclohexanone • No deactivation of the Au/MgCuCr 2 O 4 catalyst • Au Cu synergy pivotal role to high reaction rate and selectivity [ABSTRACT FROM AUTHOR]

The catalytic hydrodeoxygenation of guaiacol, a phenolic model compound of biomass lignin pyrolysis products, has been investigated under atmospheric pressure in H 2 utilizing a Ni 2 P/SiO 2 catalyst. Reaction networks are proposed based on the product distribution as a function of contact time and the temperature programmed surface reaction of adsorbed guaiacol and anisole. Guaiacol is mainly converted to benzene through demethoxylation and dehydroxylation via phenol and anisole as intermediates. Demethylation of guaiacol is a side-reaction, which produces small amounts of catechol. Spent catalyst samples were characterized by means of XRD, XPS, TEM, and temperature programmed oxidation to gain understanding the observed slight deactivation. Coke deposition, sintering, and the altering properties of Ni and P species on catalyst surface all contribute to deactivation, while there is no indication of surface oxidation after reaction. The increase of Ni δ+ or Ni 0 on the Ni 2 P surface and the decrease of Brønsted acid sites (i.e. P OH) are considered to be the major reasons of product distribution changes. [ABSTRACT FROM AUTHOR]

Silica-supported Ni 2 P catalysts were synthesized from precursors, which were either prepared by sequential impregnation of phosphorus (i.e. phosphate, phosphite and hypophosphite) on calcined NiO/SiO 2 , or by co-impregnation of nickel and phosphorus and subsequent reduction with hydrogen. Ni 2 P formation mechanisms, as investigated by means of TPR-MS, XRD and XPS, varied as a function of preparation method. Catalytic performance of the resulting Ni 2 P materials was evaluated in thiophene hydrodesulfurization; particle size was characterized by TEM. Catalysts prepared by sequential impregnation and subsequent calcination were less active than samples prepared by co-impregnation without calcination because of significantly lower Ni 2 P dispersion due to calcination. For catalysts prepared by co-impregnation the activity increased with increasing reducibility of the P precursor, i.e. in the order NH 4 H 2 PO 4 < H 3 PO 3 ≈ H 3 PO 2 . [ABSTRACT FROM AUTHOR]

The deactivation of Mo/HZSM-5 during the non-oxidative methane aromatization (MDA) reaction that yields benzene and hydrogen was investigated. Catalysts were recovered from the reactor after pre-activation and after increasing time on stream in methane. The physico-chemical properties of the spent catalysts were characterized in detail by Ar physisorption, 27 Al MAS NMR and X-ray photoelectron spectroscopy. The nature of the carbon deposits was determined by UV Raman spectroscopy and TGA, and the size and location of the Mo-carbide particles by TEM and STEM-HAADF. The results show that the main cause for catalyst deactivation is the formation of a carbonaceous layer at the external zeolite surface. This layer is made up from polyaromatic hydrocarbons and decreases the accessibility of the Brønsted acid sites in the micropores. At the same time, the decreased interaction of the Mo-carbide particles with the external zeolite surface results in their sintering. The lower Mo-carbide dispersion decreases methane conversion rates. The decreased accessibility of the Brønsted acid sites shifts the selectivity from benzene to unsaturated intermediates formed on the Mo-carbide particles. Silylation of the external surface mainly results in lower rate of coke formation at the external surface, slowing down catalyst deactivation. [ABSTRACT FROM AUTHOR]

Abstract: A thin high-silica MEL membrane was synthesized on a porous α-alumina hollow fiber support by a secondary growth approach. The membrane quality was evaluated by permporometry, single-gas permeation and butane isomer separation. Comparison of the pervaporation performance of MEL membranes with a MFI membrane of similar quality and thickness shows that MEL membranes offer a higher flux in ethanol pervaporation at nearly selectivity. [Copyright &y& Elsevier]

Highlights: [•] Au–Ir bimetallic nanoparticles explored for ethanol oxidation to acetaldehyde. [•] Au–Ir more sinter resistant under oxidative conditions than Ir. [•] Au–Ir3 composition shows significant synergy in ethanol oxidation. [•] High acetaldehyde selectivity retained for most active composition. [•] Synergy explained by mechanism involving vacant Au and Ir–O surface sites. [ABSTRACT FROM AUTHOR]

Abstract: The understanding of germanium Li-ion insertion/extraction reaction mechanism is drawing more and more attention in the field of Li-ion batteries. When a germanium thin film electrode is inserted with Li ions, the material remains amorphous until it crystallizes into Li15Ge4 as evidenced by X-ray diffraction. The local coordination environment of the Ge atoms of the intermediate amorphous phases was investigated by in situ X-ray absorption spectroscopy. Li-ion insertion and extraction were electrochemically controlled by continuous and intermittent galvanostatic methods. The evolution of the coordination number and interatomic distance of Ge–Ge and Ge–Li shells was determined as a function of Li composition. From a short range ordering perspective, it was observed that the first Ge–Ge interatomic distance increases and the Ge–Ge coordination number decreases with increasing Li content. The opposite is observed for the first Li–Ge interaction. Moreover, it was found that electrochemical lithiation is reversible at the atomic scale. [ABSTRACT FROM AUTHOR]

Abstract: In this research the effect of steps (lower coordinated surface atoms) and the presence of pre-adsorbed oxygen on the activation energy of water are studied with DFT. Without oxygen water activation is found to be structure insensitive. When oxygen is adsorbed on the surface and acts as the acceptor for the hydrogen at the step edge, the barrier will decrease significantly. [Copyright &y& Elsevier]

Abstract: A range of silica-supported gold nanoparticle catalysts have been synthesized on various silica supports. The particle size was varied between 1.7 and 15nm by varying the support (ordered mesoporous silicas, silicas with and without aluminium impurities) and the gold loading procedure. A strong influence of the gold particle size on the non-oxidative dehydrogenation of ethanol is noted: gold nanoparticles of about 6nm show a much higher activity than smaller or larger particles. This optimal catalytic activity is attributed to the existence of surface steps with a suitable geometry for the removal of β-H atoms from adsorbed ethoxide. Such stepped sites are expected to be present with maximum density for intermediate particle size. In the presence of oxygen, the rate for dehydrogenation is much higher because of the presence of an adsorbed oxygen species, but the selectivity becomes lower as combustion starts to contribute. The intrinsic activity is constant up to about 7nm and then increases for larger particles. The larger gold nanoparticles may contain strongly adsorbed oxygen adatoms, which are much scarcer on smaller gold particles. Infrared spectroscopy shows that, already at room temperature, adsorbed ethoxide reacts with molecular oxygen, whereas C–H bond cleavage to produce acetaldehyde requires at least a temperature of 75°C. The reaction rate is first order with respect to ethanol in both cases. [Copyright &y& Elsevier]

Abstract: Periodic DFT calculations show that stability of binuclear cationic gallium–oxo clusters in high-silica zeolites is mainly controlled by the favorable geometrical environment of the Ga3+ ions, whereas the effect of the direct interaction with the charge-compensating framework anionic sites is less important. Extraframework cyclic Ga2O2+ 2 cations are shown to be active for light alkane dehydrogenation. [Copyright &y& Elsevier]

Abstract: Benzene adsorption on a model for a corner site of a WS2 slab is considered by periodic DFT calculations. Under typical hydrotreating reaction conditions a fourfold coordination of the corner W atom is thought to be more favorable for benzene adsorption than five- or sixfold coordinated W atoms in conventional edge surfaces. Although no benzene adsorption site was identified on such a corner site, replacement of the W atom adjacent to the W corner site by Ni creates a potential adsorption site around the W corner site. Benzene was found to adsorb with ΔE =−0.19eV on this Ni-substituted model for the corner site of a WS2 slab. [Copyright &y& Elsevier]

Abstract: The catalytic performance of various steam-activated [Fe,Al]MFI catalysts in the direct oxidation of benzene to phenol using N2O as oxidant is described. All [Fe,Al]MFI catalysts contain ca. 90% of iron in the high-spin Fe2+ state, independent of the iron concentration (0.075–0.6wt.% iron). In the presence of N2O at 623K, most Fe2+ ions (>90%) were oxidized to Fe3+ ions as deduced from Mössbauer spectroscopy. In the presence of benzene, subsequent reduction of Fe3+ to Fe2+ takes place. However, not all of the oxidized Fe2+ to Fe3+ ions were able to selectively oxidize benzene to phenol. This indicates that only a fraction of iron is catalytically active. For [Fe,Al]MFI catalysts with relatively high iron concentration, most of the extra-framework iron species formed are inactive in the direct oxidation of benzene to phenol. Finally, a more detailed in situ Mössbauer study for one sample, i.e. [Fe,Al]MFI (1:8) catalyst, was performed to illustrate the reduction/oxidation properties of the different iron species formed after steam-treatment. [Copyright &y& Elsevier]

Saponite-like materials with Mg2+ or Ni2+ ions and their mixture in the octahedral sheet were non-hydrothermally synthesized. Their protonic forms were prepared through deammoniation or by treatment with HCl. The products were characterized by physical methods, gas-phase adsorption of amines and the catalytic transformation of 2-propanol and cumene via pulse and flow methods. The materials have a `house-of-card'' texture composed of platelets with small lateral dimensions and exhibit a high surface area and pore volume. Subsequent deammoniation resulted in the formation of non-framework Ni2+ and possibly Mg2+ ions. Mg-saponite, prepared in this way, shows predominantly non-framework species formed by tetrahedrally coordinated Al3+ ions whereas its acid-treated counterpart contains Al3+ in both framework and non-framework positions.Deammoniated Ni-saponite exhibits a peculiar catalytic behaviour, which manifests itself in the fact that the activity in the 2-propanol decomposition in a pulse experiment is low while under flow conditions it becomes the most active. This is ascribed to generation during the reaction of new acidic centres due to the dissociative adsorption of produced water on site pairs formed by coordinatively unsaturated non-framework Ni2+ and framework oxygen ions. Cumene conversion tests confirm this explanation. The high activity and stability of acid-treated Mg-saponite in cumene dealkylation underlines its potential use for high-temperature acid-catalyzed reactions. The Brønsted acidity of the saponite-like materials is related to their layer charge, cation exchange capacity and diminished with increasing Ni content, whereas the Lewis acidity increased. Both the gas-phase amine chemisorption and catalytic tests provide the same order of protonic acidity: Mg > MgNi > Ni. The origin of the acidic sites from deammoniation or HCl treatment is discussed. [Copyright &y& Elsevier]

[Display omitted] • Computational study of CO + H 2 S → COS + H 2 reaction on Cs 2 S. • Six low Miller index planes of Cs 2 S considered. • Weak CO adsorption, strong dissociative H 2 S adsorption. • COS formed via Langmuir-Hinshelwood mechanism, involving COSH* surface intermediate. • Cs 2 S (0 0 1) facet determines overall reactivity nanoparticles. Alkali metals can promote the performance of MoS 2 in methanethiol (CH 3 SH) synthesis from CO/H 2 /H 2 S mixtures. Recently, it has been found that alkali sulfides and most prominently Cs 2 S can also catalyze the reaction between CO and H 2 S to COS and H 2 , COS acting as an intermediate in CH 3 SH formation (M. Yu et al. J. Catal. 2022, 405, 116 – 128). Here, we study the nature of the active sites and the mechanism of the CO + H 2 S → COS + H 2 reaction for the 6 low-index Miller planes of Cs 2 S. While CO adsorbs weakly, strong dissociative adsorption of H 2 S results in HS* and H* intermediates, which further stabilize the (0 0 1) facet as the dominant surface termination. The main reaction pathway towards COS involves the association of CO* and SH* to COSH* followed by its dehydrogenation in a Langmuir-Hinshelwood mechanism. Reactions of CO* with lattice S atoms have prohibitively high barriers due to the strong Cs-S bonds in Cs 2 S. Overall, the reaction rate is dominated by the (0 0 1) facet with small contributions of the (0 1 0), (0 1 1) and (1 0 1) surfaces. COSH* formation, its dehydrogenation to COS, and COS desorption compete as rate-controlling steps on these surfaces. [ABSTRACT FROM AUTHOR]

Effect of phosphorus on the furfural HDO over nickel and nickel phosphide catalysts. [Display omitted] • Furfural HDO activity decreases in order: Ni 2 P ≈ MoP > Co 2 P > WP ≫ Cu 3 P > Fe 2 P. • More stable η2(C, O) adsorption on surfaces with increasing P/metal ratio. • More Brønsted acid sites with increasing P/metal ratio. • Furan-ring hydrogenation and ring opening suppressed with increasing P/metal content. • The carbonyl group conversion increased at higher P/metal ratio. The gas-phase hydrodeoxygenation (HDO) of furfural, a model compound for bio-based conversion, was investigated over transition metal phosphide catalysts. The HDO activity decreases in the order Ni 2 P ≈ MoP > Co 2 P ≈ WP ≫ Cu 3 P > Fe 2 P. Nickel phosphide phases (e.g., Ni 2 P, Ni 12 P 5 , Ni 3 P) are the most promising catalysts in the furfural HDO. Their selectivity to the gasoline additives 2-methylfuran and tetrahydro-2-methylfuran can be adjusted by varying the P/Ni ratio. The effect of P on catalyst properties as well as on the reaction mechanism of furfural HDO were investigated in depth for the first time. An increase of the P stoichiometry weakens the furan-ring/catalyst interaction, which contributes to a lower ring-opening and ring-hydrogenation activity. On the other hand, an increasing P content does lead to a stronger carbonyl/catalyst interaction, i.e., to a stronger η2(C, O) adsorption configuration, which weakens the C1 O1 bond (Scheme 1) in the carbonyl group and enhances the carbonyl conversion. Phosphorus species can also act as Brønsted acid sites promoting C1 O1 (Scheme 1) hydrogenolysis of furfuryl alcohol, hence contributing to higher production of 2-methylfuran. [ABSTRACT FROM AUTHOR]

Cobalt oxidation is a relevant deactivation pathway of titania-supported cobalt catalysts used in Fischer-Tropsch synthesis (FTS). To work towards more stable catalysts, we studied the effect of the surface area of the titania support and noble metal promotion on cobalt oxidation under simulated high conversion conditions. Mössbauer spectroscopy was used to follow the evolution of cobalt during reduction and FTS operation as a function of the steam pressure. The reduction of the oxidic cobalt precursor becomes more difficult due to stronger metal-support interactions when the titania surface area is increased. The reducibility was so low for cobalt on GP350 titania (surface area 283 m2/g) that the catalytical activity was negligible. Although cobalt was more difficult to reduce on P90 titania (94 m2/g) than on commonly used P25 titania (50 m2/g), the Co/P90 catalyst showed increased resistance against cobalt sintering and higher FTS performance than Co/P25. The addition of platinum to Co/P90 led to a higher reduction degree of cobalt and a higher cobalt dispersion, representing a catalyst with promising performance at relatively low steam pressure. Nevertheless, the stronger cobalt-titania interactions result in more extensive deactivation at high steam pressure due to oxidation. [Display omitted] • Cobalt Fischer-Tropsch catalyst studied by operando Mössbauer spectroscopy. • Impact of humid conditions on cobalt phase changes investigated. • Cobalt reducibility suppressed on TiO 2 with higher surface area (GP-350

• Pd & Pd-Pt on various aluminosilicate evaluated for n-C 16 hydroconversion. • Preference CH 3 branching central positions in monobranched isomers at low X n-C16. • Preference CH 3 far from center in dibranched isomers at higher X n-C16. • With increasing X n-C16 : cracked product distribution from M shape to symmetric shape. • No preferential sieving of isomers in n-C 7 hydroconversion. The mechanism of n-hexadecane (n-C 16) hydroisomerization/hydrocracking was studied over bifunctional catalysts employing Pd and Pt as (de)hydrogenation components and large-pore zeolites and (ordered) mesoporous materials as acidic supports. Zeolite Y and Beta supports were compared to amorphous silica-alumina as well as aluminium-containing ordered mesoporous MCM-41, MCM-48 and SBA-15 materials to cover a wide range of pore sizes and topologies. Products were analyzed in terms of mono- and di-branched C 16 isomers and cracked products as a function of the n-C 16 conversion. All samples followed a similar mechanism in which, at low conversion, di-branched isomers with methyl groups toward the ends of the tetradecane chain were observed. At higher conversion, the products shifted to isomers with methyl groups closer to the center at higher n-C 16 conversion. Consistent with these differences, the typical 'M' shape distribution of cracked products was obtained at low conversion, which evolved into ideal symmetric cracking patterns at higher conversion. The unusual di-branched isomer distribution at low conversion and the corresponding 'M' shaped cracked products distribution have earlier been associated with pore mouth catalysis induced by restricted diffusion in medium-pore zeolites. Here we show that such reaction pathways also occur in catalysts with large enough pores to exclude diffusion restrictions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Methanol-to-hydrocarbons on HZSM-5, Ca/ZSM-5, and Na/ZSM-5 investigated. • Comparison rate and deactivation constants: Ca/ZSM-5 least active sample. • Step-response IR experiments: H 2 O, methanol, and dimethylether interact with Ca2+. • Adsorbates on Ca2+ affect pore occupancy and product distribution. • Trade-off between activity and olefin selectivity for Ca/ZSM-5. Establishing structure–activity relationships for the methanol-to-hydrocarbons reaction can help to identify better catalysts and optimal reaction conditions. Modification of ZSM-5 catalysts with alkaline-earth cations such as Ca increases the selectivity to C 3+ olefins, which has been linked to a change in the effective pore geometry, affecting the formation of particular hydrocarbon pool (HCP) components. To further understand the catalytic properties of Ca/ZSM-5, we estimated the methanol conversion rate constants and deactivation coefficients. The kinetic experiments were carried out at different contact times with and without water in the feed. Ca/ZSM-5 is substantially less active than HZSM-5 and Na/ZSM-5 in a wide range of conditions. The decreased activity can be correlated to a different composition of the HCP due to the presence of Ca, which is supported by step-response IR experiments using various feed mixtures (methanol, methanol + water, water). Ca/ZSM-5 converts methanol significantly slower than HZSM-5 and Na/ZSM-5 but with a higher C 3+ olefins selectivity, pointing to the delicate balance between activity and selectivity in these materials. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Resulfidation restores (Ni/Co)MoS2 slabs lost after oxidation. • Mo and S are completely resulfided; Co and especially Ni are not. • Oxidation-resulfidation increases thiophene HDS performance. • Smallest slabs are lost upon oxidation-resulfidation. • Thiophene HDS. Abstract The effect of a sequential oxidation and resulfidation treatment on γ-Al 2 O 3 supported (Ni/Co)MoS 2 catalyst nanoparticles was investigated using (HR)TEM, XPS, and thiophene HDS catalytic performance experiments. Analysis of the HRTEM images revealed that, after initial sulfidation and oxidation, the resulfidation treatment restored the original slab length or increased it. The chemical composition of the samples, as determined by XPS, also slightly changed: the concentration of oxidic species increased, especially for the Ni promoter atoms. Comparing the catalytic HDS activity of the samples before and after the oxidation-resulfidation treatment showed that the catalysts were more than 20% more active after resulfidation. This increase in HDS activity is ascribed to a redistribution of the (Ni/Co)MoS 2 slabs during the second sulfidation treatment, indicating a size effect. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The first in-situ XAS study on Au and Pd during the direct synthesis of H 2 O 2 at relevant conditions. • Catalytic microreactor used as safe, portable and free of transport- effects spectroscopic cell. • Metallic Pd is the active phase for the direct synthesis of H 2 O 2 using both Pd and AuPd catalysts. • Unlike AuPd, monometallic Pd forms Pd-H during reaction, which may explain its lower selectivity. Abstract For the first time, we perform in-situ X-Ray Absorption Spectroscopy on both Au L 3 and Pd K edges during the direct synthesis of hydrogen peroxide in a high-pressure gas-liquid-solid microreactor using SiO 2 supported Pd, Au and AuPd catalysts under relevant reaction conditions. The catalysts were coated on the walls of 320 µm ID micro capillaries, used in this work both as microreactors and as spectroscopic cells, ensuring safety of operation, ease of portability and absence of reactor effects during the measurements. XANES analysis revealed that the fresh Pd and AuPd catalysts contained a mix of Pd/PdO phases which was readily reduced in H 2 atmosphere. The presence of only metallic Pd under reaction conditions for both catalysts proved that metallic Pd is the active phase for this reaction. Au was present in its metallic form in both Au and AuPd under all conditions tested. Unlike the AuPd, monometallic Pd showed an increase in the Pd-Pd distance under reaction conditions, attributed to the formation of Pd-hydride. We propose that the absence of Pd-hydride in the AuPd catalysts reduces further hydrogenation of H 2 O 2 to water, thereby explaining the increased selectivity to H 2 O 2 observed with AuPd catalysts. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • In-situ DRIFTS on adsorbed CO was employed to study UV induced charge transfer in Pt-TiO 2 P25. • Largest UV-induced shift is +0.5 cm−1 for CO adsorbed on atomic Pt species. • CO adsorbed on large Pt clusters or particles does not experience large shifts upon illumination. • Contrary to solid–liquid interfaces, shifts of ν(CO) at the solid–gas interface are small. Abstract The efficiency of photocatalytic systems is strongly depending on the charge carrier transfer from the excited semiconductor to co-catalyst particles attached on its surface. In this study, we investigated the influence of photo-induced charge transfer in photoplatinized TiO 2 P25 photocatalysts by diffuse reflectance FTIR spectroscopy of CO molecules adsorbed on the Pt co-catalyst under well-defined gas phase conditions. In contrast to aqueous conditions, where shifts of the CO stretching vibration of up to 50 cm−1 have been reported, the observed shifts under gas phase conditions are very small (<1 cm−1). This demonstrates that the difference in dielectric properties between aqueous electrolytes and vacuum are critical for the development of prominent shifts of adsorbed CO bands upon trapping of photogenerated charge carriers on co-catalyst particles. The experimental findings are discussed in terms of an electrostatic Stark effect, charge screening, co-adsorption, coverage-dependent shifts of the vibrational bands of adsorbed CO and photocatalytic surface reactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect Mn promotion Co-catalyzed Fischer-Tropsch reaction strongly pressure dependent. • MnO dispersed on Co metal particles provides additional sites for CO dissociation. • Mn raises selectivity at low pressure and promotes CO dissociation not chain growth. • At low pressure, Mn enhances activity and C 5+ selectivity. • At high pressure, Mn enhances activity but lowers C 5+ selectivity. The mechanism of Mn promotion of a silica-supported Co catalyst in the Fischer-Tropsch reaction has been studied at varying pressures up to 20 bar. IR spectroscopy in combination with DFT calculations suggest adsorbed CO is activated by reaction with an oxygen vacancy in the MnO, which covers the Co surface. This leads to a higher activity, higher CH x coverage and thus higher C 5+ and lower CH 4 selectivity. Increasing the pressure magnifies the selectivity differences. However, above around 4 bar, the effect of Mn on the selectivities is reversed and the C 5+ selectivity is decreased by Mn addition. This is tentatively attributed to Mn promoting the C-O bond dissociation but not the chain growth. Formed monomers have to migrate to stepped sites for chain growth on the Co surface. Whilst this is migration is not impeded by co-adsorbates at low pressure, migration could be hindered by especially the high CO coverage at high pressure. [ABSTRACT FROM AUTHOR]

This paper explores the environmental and economic aspects of fast pyrolytic conversion of lignin, obtained from 2G ethanol plants, to transport fuels for both the marine and automotive markets. Various scenarios are explored, pertaining to aggregation of lignin from several sites, alternative energy carries to replace lignin, transport modalities, and allocation methodology. The results highlight two critical factors that ultimately determine the economic and/or environmental fuel viability. The first factor, the logistics scheme, exhibited the disadvantage of the centralized approach, owing to prohibitively expensive transportation costs of the low energy-dense lignin. Life cycle analysis (LCA) displayed the second critical factor related to alternative energy carrier selection. Natural gas (NG) chosen over additional biomass boosts well-to-wheel greenhouse gas emissions (WTW GHG) to a level incompatible with the reduction targets set by the U.S. renewable fuel standard (RFS). Adversely, the process’ economics revealed higher profits vs. fossil energy carrier. [ABSTRACT FROM AUTHOR]

At a first glance, ethanol, toluene and methyl tert-butyl ether look nothing alike with respect to their molecular structures. Nevertheless, all share a similarly high octane number. A comprehensive review of the inner workings of such octane boosters has been long overdue, particularly at a time when feedstocks for transport fuels other than crude oil, such as natural gas and biomass, are enjoying a rapidly growing market share. As high octane fuels sell at a considerable premium over gasoline, diesel and jet fuel, new entrants into the refining business should take note and gear their processes towards knock resistant compounds if they are to maximize their respective bottom lines. Starting from crude oil, the route towards this goal is well established. Starting from biomass or natural gas, however, it is less clear what dots on the horizon to aim for. The goal of this paper is to offer insight into the chemistry behind octane boosters and to subsequently distill from this knowledge, taking into account recent advances in engine technology, multiple generic design rules that guarantee good anti-knock performance. Careful analysis of the literature suggests that highly unsaturated (cyclic) compounds are the preferred octane boosters for modern spark-ignition engines. Additional side chains of any variety will dilute this strong performance. Multi-branched paraffins come in distant second place, owing to their negligible sensitivity. Depending on the type and location of functional oxygen groups, oxygenates can have a beneficial, neutral or detrimental impact on anti-knock quality. [ABSTRACT FROM AUTHOR]

The fundamental aspects of Brønsted acidity and catalytic reactivity of faujasite-type zeolites were investigated by periodic DFT calculations. The adsorption energies of ammonia and pyridine on the Brønsted acid site (BAS) were used to determine the acidity. It is demonstrated that the acid strength of zeolite materials increases with rising Si/Al ratio (low-silica faujasite), and then levels off at high Si/Al ratio (high-silica faujasite). The presence of multinuclear extra framework Al (EFAl) in the sodalite cages substantially enhances the Brønsted acidity. The catalytic reactivity of faujasite toward protolytic propane cracking correlates well with the characterized acidity by base adsorption. However, for H/D exchange reaction of benzene the presence of EFAl species can induce deviations between the measured acidity and the reactivity of faujasite catalysts, indicating that acidity and reactivity are not always directly correlated. [ABSTRACT FROM AUTHOR]

The performance of a range of nanoparticulate gold catalysts in the hydrogenation of carbon dioxide to formates was investigated and a superior performance of Au/Al 2 O 3 was revealed. The comparative studies with unsupported gold nanoparticles pointed to the crucial role of the metal–support interaction for the CO 2 hydrogenation activity. Cyanide leaching tests complemented by XPS and STEM studies point to the importance of metallic Au 0 species for the catalytic activity. The Au/Al 2 O 3 catalyst shows stable activity that allows reaching equilibrium formate yields in a broad temperature range. A kinetic study revealed that a near-zero apparent activation barrier for the hydrogenation reaction is an intrinsic property of the catalytic system. The reaction mechanism is proposed on the basis of the obtained reactivity and characterization data. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxidation of metallic cobalt occurs under relevant Fischer-Tropsch (FTS) conditions. • The extent of oxidation up to around 1.2w% is independent of cobalt weight loading. • Interaction between cobalt and surface titanols are key to the oxidation behavior. • Metal-support compounds only form at very high oxidizing potential in absence of CO. • Oxidation and sintering are linked and steam induces particle growth. The study of titania-supported cobalt nanoparticles is relevant for industrial Fischer-Tropsch synthesis (FTS). Herein, we report about various deactivation pathways of cobalt supported on P25 titania (cobalt loading 2–8 wt%) under simulated high conversion conditions using in situ Mössbauer spectroscopy. A fraction of metallic cobalt was oxidized under humid FTS conditions. The absolute amount of oxidized cobalt was ∼ 1.2 wt% independent of the cobalt loading, indicating that specific cobalt-titanol interactions are involved in the oxidation process. The formation of cobalt-titanate-like compounds was only observed under very high water-to-hydrogen ratios in the absence of carbon monoxide. Steam considerably enhances cobalt sintering under FTS conditions. As such, deactivation under humid FTS conditions is not only caused by cobalt oxidation but also by enhancing sintering of the active phase. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbon removal rate-limiting for Fe-carbide in the Fischer-Tropsch (FT) reaction. • C deposits decrease FT activity and increase CH 4 selectivity. • SSITKA investigations used as function of amount of C deposits. • Slow sites mainly responsible for CH 4 formation via MvK mechanism. • Higher H 2 /CO ratio or total pressure removes C deposits and decreases deactivation. A well-known observation in the Fe-catalyzed Fischer-Tropsch (FT) reaction is that Fe-carbide catalysts deactivate due to carbon deposition. In comparison, the influence of such carbon deposits on the product distribution has been less widely reported. The present work investigates the relationship between the kinetics of the FT reaction for a carburized Raney-Fe model catalyst and the composition of the catalytic surface with a focus on carbon deposits. The deposition of carbon during the ongoing FT reaction at low pressure decreases the FT activity and increases the CH 4 selectivity. Steady-state transient isotopic kinetic analysis (SSITKA) at low pressure shows that the buildup of C deposits affects fast CO conversion sites on the Fe-carbide surface, mainly responsible for C C coupling via a Langmuir-Hinshelwood mechanism, more than slow sites that mainly produce CH 4 via a Mars-Van Krevelen mechanism. Hindrance of migration of chain-growth monomers by C deposits decreases the amount of longer hydrocarbons. Nevertheless, SSITKA shows that C 2 products form faster, which is likely since their formation increasingly depends on monomers formed at proximate CO dissociation sites when the amount of carbon deposits increases. Carbon deposition can be suppressed and reversed by increasing the H 2 /CO ratio at constant pressure or by increasing the total pressure at constant H 2 /CO ratio. As such, the FT performance can be stabilized by operating at elevated pressure, even if initially the reaction was started at low pressure. Nevertheless, prolonged operation at low pressure leads to a less reactive character of the C deposits that cannot be removed anymore during high-pressure operation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cr promotes CO 2 hydrogenation to CH 3 OH in In 2 O 3 catalysts. • Cr doping facilitates the formation of oxygen vacancies in In 2 O 3. • Cr-oxide clusters on In 2 O 3 destabilizes oxygen vacancies in nearby In 2 O 3. • Cr-oxide clusters suppress reduction-induced sintering of In 2 O 3. • The additive effect of Ni and Cr enhances methanol synthesis in Ni-In 2 O 3 -CrO x. The utility of Cr as a promoter for In 2 O 3 catalysts in the hydrogenation of CO 2 to methanol is investigated. Uniform precursors to binary CrO x -In 2 O 3 and ternary NiO-CrO x -In 2 O 3 catalysts are prepared by flame spray pyrolysis. For the CrO x -In 2 O 3 samples, the highest methanol rate is obtained at a Cr content of 2 mol%, exceeding the methanol rate of In 2 O 3 by 55 %. With increasing Cr content, the CO 2 conversion rate does not increase, albeit the methanol selectivity decreases. Characterization of the samples supported by density functional theory calculations provides insight into the role of Cr. At low content, Cr is mainly doped into the lattice of In 2 O 3, which leads to more oxygen vacancy (O v) sites. The In 2 O 3 surface sites close to Cr-oxide clusters present on the surface are also activated towards O v formation, offsetting the decrease in O v due to coverage of the In 2 O 3 surface by Cr-oxide with increasing Cr content. Cr 2 O 3 dispersed on the surface of the In 2 O 3 particles suppresses sintering of In 2 O 3 under reducing conditions, which is especially evident at a Cr content above 2 mol% and higher reaction temperatures. Introducing Ni to the CrO x -In 2 O 3 catalysts results in a higher methanol formation rate compared to CrO x -In 2 O 3. The methanol rate increases with the Ni content with the highest activity obtained at Ni and Cr contents of 22 mol% and 8 mol%, respectively. The optimum Ni(22)-Cr(8)-In 2 O 3 catalyst displays twice the methanol rate of a Ni(22)-In 2 O 3 reference. Ni and Cr play different promoting roles in achieving an increased and more stable rate of methanol formation compared to In 2 O 3 : Ni promotes the hydrogenation of formate and methoxy surface intermediates to methanol, while Cr results in more O v sites and suppresses sintering of In 2 O 3. [ABSTRACT FROM AUTHOR]

[Display omitted] • Impact manganese on cobalt Fischer-Tropsch synthesis (FTS) catalyst investigated. • Steam accelerates sintering of metallic cobalt under synthesis gas conditions. • Manganese oxide promotion enhances sintering resistance of metallic cobalt in FTS. • Manganese oxide and cobalt are mobile under simulated high conversion conditions. • Strong manganese-cobalt interaction results in carbidisation under FTS conditions. The commercial application of cobalt-based Fischer-Tropsch synthesis (FTS) suffers from catalyst deactivation. One of the main deactivation mechanisms under industrial conditions is sintering. In this work, we explored the role of manganese oxide as a structural promoter against sintering in a carbon nanofiber supported cobalt model catalyst. We employed in situ Mössbauer emission spectroscopy to study cobalt sintering in synthesis gas as a function of the steam partial pressure, which mimics high CO conversion during FTS. Steam accelerates the sintering of non-promoted metallic cobalt particles. Model experiments point to a synergistic effect between carbon monoxide and steam on cobalt sintering. In the mangense-promoted case, sintering is significantly reduced, indicative of the structural stabilization of small cobalt particles by manganese oxide. Nevertheless, a fraction of cobalt particles in close interaction with manganese oxide carburized under these conditions, resulting in a lower catalytic activity. [ABSTRACT FROM AUTHOR]

We investigated the influence of Pt particle size and the addition of Re in carbon-supported catalysts in the aqueous phase reforming (APR) of glycerol. Pt nanoparticles with averaged sizes of 1.2, 1.6, 2 and 4.2 nm were obtained by reduction at increasing temperatures of Pt/C. Gas-phase water–gas shift (WGS) and acetaldehyde decomposition reactions were used to separately study important reaction steps in the APR mechanism. The APR H 2 turnover frequency, which was highest for 2 nm Pt particles, correlates with activity trends in the WGS reaction. The decarbonylation rate (acetaldehyde decomposition) is also highest for intermediate Pt particle size. Pt–Re nanoparticles were prepared by in situ catalytic reduction of HReO 4 on Pt/C followed by reduction at 300 °C. The APR activity after Re addition on Pt/C increased for Pt/C–Re having initial the smallest particles, but decreased for the other larger-sized Pt/C–Re catalysts. The bimetallic catalysts were much more active in the WGS reaction than their Pt-only parents. An increase in the reduction temperature to 600 °C resulted in a further increase of the WGS activities. The different ways Re addition affects APR and WGS activities of Pt/C catalysts relate to different surface site requirements for these reactions. The presence of isolated Pt atoms, whose fraction increases when the alloys are reduced at higher temperatures, is sufficient to bring about the synergetic effect between Pt and Re for the WGS reaction. For APR, on the other hand, the presence of surface ensembles of Pt atoms is essential for obtaining high C O and C C bond breaking rates. [ABSTRACT FROM AUTHOR]

The increasing availability of computational data from quantum-chemical calculations on the reactivity and electronic structure of catalytically active oxidic systems make a revisitation of the classical questions on chemical bonding aspects of catalytically reactive systems useful. This Perspective paper starts with a short review of the different available systems. The elementary reactions that are part of the selective oxidation catalysis, such as substrate bond activation or oxygen insertion, are introduced. This is followed by a discussion of basic electronic features of the valence electron structure of oxide materials. We will initially compare the chemical bonding and reactivity of compounds with dominantly ionic versus covalent bonding. Surface reactivity descriptors for the two types of chemical bonds are indicated. It will appear that, except for longer range ionic interactions, binding to the metal cations is dominated by local covalent interactions and that ligand field theory type atomic orbital splitting as well as rehybridisation are important. Trends in bonding as a function of position of reducible metal in the periodic system are emphasized throughout the paper. At the surface, in addition to the changes in electronic structure, atom position relaxation and surface reconstruction effects may also have a large influence on the differences in reactivity. The reactivity of the oxygen atoms varies. They can be proton acceptors and generate Brønsted acidity, can assist heterolytic or radical type C H bond activation or when electrophilic will insert into hydrocarbon double bonds. At the end of the paper trends in catalytic reactivity are analyzed. The double volcano type curve found for the dependence of catalytic reactivity on the position of cation in the third row of the periodic system is shown to relate to the distribution of electrons with high spin over the ligand field split atomic orbitals of the respective cations. This will be discussed in the context of classical catalytic results that are based on Balandin type volcano plots of reactivity versus the catalyst material reactivity parameters. [ABSTRACT FROM AUTHOR]

The catalytic performance in n-hexadecane hydrocracking of a set of bifunctional catalysts composed of acidic mesoporous silicas, i.e., SBA-15, MCM-41, MCM-48, and amorphous silica-alumina (ASA), and Pd as acid and (de)hydrogenation components, respectively, was investigated. The selectivity to cracked products and the occurrence of secondary cracking depended on the pore topology, acidity, and Pd dispersion. The Si/Al ratio and the mesopore order of SBA-15 were modified by changing the pH in the synthesis step. Al was introduced in the M41S materials by post-synthesis grafting. All materials including ASA exhibited low acidity compared to crystalline zeolites. Increasing Al content led to a decrease of the order of mesopores. Secondary cracking of n-hexadecane was more pronounced for catalysts containing long one-dimensional cylindrical pores (SBA-15 and MCM-41) in comparison with catalysts containing three-dimensional ordered (MCM-48) or disordered (ASA) mesopores. The selectivity difference is attributed to differences in residence time of intermediates in the mesopores. The distance between acid sites located in mesopores and Pd nanoparticles primarily located outside these pores also influences the product distribution. Ideal hydrocracking operation is approached for ASA, MCM-48, and SBA-15 prepared at a high pH containing disordered mesopores. • Pd/mesoporous silica (MCM-41, MCM-48, SBA-15 ASA) evaluated in n-C 16 hydroconversion. • Cracked product contribution decreases with loss of mesopores. • Low Pd dispersion results in overcracking due to long poor residence time of olefins. • Well-ordered mesoporosity leads to more cracking than disordered mesoporosity. • Asymmetric cracked product distribution for all samples [ABSTRACT FROM AUTHOR]

Highlights: [•] High-silica MFI and MEL membranes synthesized by microwave secondary growth. [•] Surface modification with triethoxyfluorosilane (TEFS). [•] TEFS enhances hydrophobic properties, heals defects within zeolite layer. [•] Membrane performance in recovery of ethanol from water improved. [ABSTRACT FROM AUTHOR]

Highlights: [•] Dual synergy between Au and Cr-hydrotalcite in liquid-phase alcohol oxidation. [•] Facile O2 activation by a Cr3+ ↔Cr6+ redox cycle at the gold-support interface. [•] Electron transfer from Cr-hydrotalcite to Au during Cr oxidation. [•] α-C–H bond cleavage controls the rate to greater extent than O–H bond cleavage. [•] Increasing Cr content and decreasing Au particle size enhance Au–Cr synergy. [Copyright &y& Elsevier]

Highlights: [•] Tunable basicity of calcined hydrotalcites by doping with transition metal cations. [•] Optimum basicity achieved by adjusting calcination temperature. [•] Green synthesis of glycerol carbonate by calcined hydrotalcites. [•] Good correlation between catalytic activity and surface basic site density. [•] Ni2+ doping and calcination at 500°C maximize basicity and activity. [ABSTRACT FROM AUTHOR]

Transition metals, such as Ni, Pd, and Pt, and ZrO 2 are known as efficient promoters in M-In 2 O 3 -ZrO 2 catalysts for CO 2 hydrogenation to methanol. Herein, we systematically investigated the role of Ni and ZrO 2 promoters by preparing ternary NiO-In 2 O 3 -ZrO 2 catalysts and binary counterparts by flame spray pyrolysis. The highest methanol rate was obtained for the Ni(6 wt%)-In 2 O 3 (31 wt%)-ZrO 2 (63 wt%) composition. DRIFTS-SSITKA shows that formate is the key intermediate in the hydrogenation of CO 2 to methanol. Kinetic analysis shows the competition between methanol and CO formation. The rate-limiting step in methanol formation is likely the hydrogenation of surface methoxy species. Ni and ZrO 2 play different promoting roles without showing synergy with respect to each other. Ni promotes hydrogenation of surface formate and methoxy species, while ZrO 2 maintains a high In 2 O 3 dispersion, the smaller In 2 O 3 size likely stabilizing formate and other intermediates during their conversion to methanol. [Display omitted] • Ni-In 2 O 3 -ZrO 2 present high activity in CO 2 hydrogenation to methanol. • Reaction mechanism: adsorbed CO 2 → HCOO* → CH 3 O* → methanol. • Ni promotes hydrogenation of formate and methoxy surface intermediates. • ZrO 2 stabilizes small In 2 O 3 particles and the conversion of intermediates. • Easier hydrogenation for smaller In 2 O 3 particles stabilized by ZrO 2. [ABSTRACT FROM AUTHOR]

Abstract: Two metal organic frameworks (MOFs), chromium benzenedicarboxylates MIL-101 and MIL-53, have been synthesized and used as the support of palladium catalysts. The palladium catalysts were characterized by XRD, TEM, and CO chemisorption. MIL-101 is highly hydrophilic and beneficial as support for fine Pd nanoparticles with an average size of 2.3nm. Microporous MIL-53 is relatively hydrophobic and larger Pd particles with an average size of 4.3nm were formed on the external surface. Pd/MIL-101 showed better phenol selective hydrogenation activity to cyclohexanone (>98%) under mild reaction conditions because of its smaller particle size. [Copyright &y& Elsevier]

• Electrochemical CO 2 reduction on Cu 8 /SnO 2 (110) studied by DFT and microkinetics. • High vs. low H coverage compared Cu 8 H 6 /SnO 2 (110) vs. Cu 8 /SnO 2 (110). • Genetic algorithms and Monte Carlo methods explore stable structure clusters. • Distinct CO 2 adsorption modes at Cu 8 -SnO 2 interface lead to distinct pathways. • High H coverage leads to HCOOH formation, low H coverage to CO. The electrochemical reduction of CO 2 (eCO 2 R) is a promising approach for converting CO 2 into valuable chemicals and fuels using renewable energy sources. We investigated the mechanism of eCO 2 R for a small Cu 8 cluster placed on SnO 2 containing O vacancies using density functional theory and predicted current density and selectivity by microkinetics simulations within the computational hydrogen electrode model. Low and high H coverages were modeled by Cu 8 /SnO 2-x and Cu 8 H 6 /SnO 2-x models, using statistical methods to identify their most stable structures. Different CO 2 adsorption modes on Cu 8 /SnO 2-x and Cu 8 H 6 /SnO 2-x surface models, all containing an O vacancy, resulted in distinct reaction pathways, leading to either HCOOH or CO. The preferred formation of HCOOH occurred upon CO 2 adsorption on an O vacancy on the Cu 8 H 6 /SnO 2-x surface, followed by sequential hydrogenation to HCOO and HCOOH. Adsorption of CO 2 on Cu 8 /SnO 2-x opened a facile pathway to CO. Electronic structure analysis revealed that differences in charge donation of Cu to the antibonding orbitals of CO 2 can explain the predicted selectivity differences. The preferred adsorption mode of CO 2 is bidentate at the Cu-SnO 2-x interface. Our findings emphasize the role of H coverage on Cu on the selectivity of eCO 2 R for Cu/SnO x catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] Tunable basicity of calcined LDH by changing Mg/Al ratio and calcination temperature. [•] Green synthesis of glycerol carbonate by calcined MgAl mixed oxides. [•] Catalytic activity correlates with surface basic site density. [•] Catalyst with Mg/Al=2 and calcination at 600°C optimum basicity and activity. [ABSTRACT FROM AUTHOR]

Abstract: A comprehensive DFT study of acid-catalyzed glucose and fructose reactions in water covering more than 100 potential reaction paths is performed with the aim to identify the main reaction channels for obtaining such desirable biorefinery platform products as 5-hydroxymethylfurfural (HMF) and levulinic acid (LA). Characteristic for fructose dehydration by Brønsted acids is the preferred protonation of the O2H group at the anomeric carbon atom, which initiates a sequence of facile reactions toward HMF. Further rehydration to LA is more difficult and competes with condensation reactions leading to humins. A very different result is obtained when glucose is the reactant. The preferred protonation site is the O1H hydroxyl group. The associated reaction paths do not lead to the formation of HMF or LA but result in humin precursors and reversion products. Protonation of other sites occurs at a much lower rate. Nevertheless, when glucose is activated at these less reactive sites, it can lead to LA via a reaction mechanism that does not involve the intermediate formation of fructose and HMF. This direct mechanism is argued to be preferred over the conventional sequential conversion scheme. It is concluded that the differences in the reactivity of glucose and fructose in acidic aqueous solutions are dominated by the regioselectivity of the initial protonation step. [Copyright &y& Elsevier]

Abstract: A series of Rh nanoparticles with sizes between 3.5 and 11.4nm were synthesized in the presence of polyvinylpyrrolidone and evaluated for their performance as catalysts in the hydrogenation of phenylacetylene and 1-octene. The reaction is zeroth order in the reactant for phenylacetylene and 1-octene. The catalytic activity increased with Rh particle size in the hydrogenation of phenylacetylene, whereas the activity in 1-octene hydrogenation did not depend on particle size. The possible explanations for this different particle size behavior are discussed. [Copyright &y& Elsevier]

Abstract: In the search for active and stable Ni-based catalysts for steam methane reforming in membrane reactors, the effect of three different promoters La, B and Rh was compared. Promoted and unpromoted Ni catalysts were characterized by TEM, TPR and X-ray absorption spectroscopy. The average Ni particle size is between 4 and 10nm. Promoters affected both dispersion and reducibility of Ni. Smaller particles were found to be more difficult to reduce than larger ones. The use of B resulted in very small Ni particles. The degree of Ni reduction strongly increased by use of La and Rh promoters, whereas B strongly impeded Ni reduction. The initial intrinsic rate per surface metal atom was found to increase linearly with the Ni metal dispersion, suggesting that the rate is controlled by dissociative methane adsorption over low-coordinated surface atoms. The data indicate that Rh and La act as structural promoters to the activity. Catalysts modified by B show a much higher activity of the Ni surface atoms. Catalyst stability was investigated by using feed compositions representing the inlet of the membrane reactor and the hydrogen lean reformate towards its outlet. Stability increases in the order La

Abstract: A nanostructured Au/TiO2@SBA-15 catalyst has been prepared and applied in propylene epoxidation with a mixture of O2/H2. The mesopores of SBA-15 were first deactivated by grafting of hydrophobic groups. Titanium was then selectively grafted in the micropores of SBA-15 by reaction with titanium isopropoxide followed by calcination and deposition of Au nanoparticles. The nanocomposite catalysts exhibited relatively stable propylene oxide (PO) production with small amounts of propanal and acetone byproducts. A catalyst prepared by grafting with trimethylsilyl groups, a Ti/Si ratio of 0.05 and very small Au nanoparticles (<2nm), showed the highest catalytic activity. The improved performance appears to be related to the interaction of very small Au nanoparticles in close contact with very small sized TiO2 domains in combination with the hydrophobicity of the fully open mesopores. The results demonstrate the possibility to improve the catalytic performance of Au–Ti catalysts through rational catalyst design. [Copyright &y& Elsevier]

Abstract: Ordered mesoporous materials (SBA-15 and KIT-6 silica and MFI zeolite) supported nickel phosphide (Ni x P y ) hydrotreating catalysts were prepared by reduction of oxidic precursors with an initial stoichiometric Ni/P ratio of 2 The metal loading (20 and 30wt.% Ni x P y ) and pretreatment conditions (773K or 873K reduction temperature, in situ sulfidation at 723K) of the precursors were varied. Temperature programmed reduction, in situ XRD, and 31P NMR indicate the formation of metallic nickel then different nickel phosphides (Ni3P, Ni12P5, then Ni2P) in this order upon reduction. The changes in the textural properties of the catalysts compared to their parent supports promote the conclusion that a significant part of the Ni x P y phases is located inside the mesopores. The catalytic activity (parallel dibenzothiophene hydrodesulfurization and o-methyl aniline hydrodenitrogenation) increases strongly with increasing Ni x P y loading. The KIT-6 and SBA-15 supported catalysts exhibit higher hydrotreating activities than reference CoMo/Al2O3 and Ni12P5/SiO2 catalysts. In contrast, the catalyst based on a mesoporous MFI support had the lowest hydrotreating activity. This activity trend is explained by the propensity of high-surface area mesoporous silica supports to well disperse metal phosphide particles. The active phase composition of the spent catalysts is in the range of Ni2.0–2.6P1.0S0.4–0.7. This suggests that bulk Ni2P with some sulfur in its surface forms the active phase in the mesopores of SBA-15 and KIT-6. [Copyright &y& Elsevier]

Abstract: The stability of various gallium species (Ga+, , and GaH+2) as models for the active sites in reduced Ga/ZSM-5 and the possible reaction paths of alkane dehydrogenation were studied using a density functional theory cluster modeling approach. In general, alkanes are preferentially activated via an “alkyl” mechanism, in which gallium acts as an acceptor of the alkyl group. A comparison of the computed energetics of the various reaction paths for ethane indicates that the catalytic reaction most likely proceeds over Ga+. The initial step of Cion is the oxidative addition of an alkane molecule to the Ga+ cation, which proceeds via an indirect heterolytic mechanism involving the basic oxygen atoms of the zeolite lattice. Although the catalytic reaction can also occur over and GaH+2 sites, these paths are not favored. Decomposition of leading to formation of Ga+ during the catalytic cycle is more favorable than regeneration of these sites. The reactivity of GaH+2 ions is strongly dependent on the distance between the stabilizing aluminum-occupied oxygen tetrahedra. In cases of greater Alces, the stability of the GaH+2 species is very low, and it decomposes to Ga+ and a Brønsted acid site, whereas when Al atoms are located more closely, the charge-compensating GaH+2 ions are the most stable and exhibit the lowest activity for the initial Ceavage reaction. [Copyright &y& Elsevier]

Abstract: Several reconstructions of catalytic active sites in gallium-exchanged mordenite have been analyzed using periodic density functional theory method. It is found that a number of structures in which gallium is present as Ga(III)H x , Ga(II)Ga(II)H x , and Ga(III)Ga(I)H x can be reached under alkane dehydrogenation conditions. The transition barrier for the rate determining step in alkane dehydrogenation are evaluated. The values indicate that these gallium structures can catalyze alkane dehydrogenation and suggest an alternative reaction route in addition to those that have been proposed before. To cite this article: X. Rozanska et al., C. R. Chimie 8 (2005). [Copyright &y& Elsevier]

Abstract: The concentration dependence of the self-diffusivity of n-hexane in large crystals of silicalite-1 and HZSM-5 zeolites has been investigated with positron emission profiling (PEP) in the temperature range of 393–483K. A monotonic increase in the diffusivity was observed with increasing alkane loading for both zeolites up to 4 molecules per unit cell. The diffusion coefficient in HZSM-5 was approximately half of that in silicalite-1 due to the interaction of n-hexane with the Brønsted acid sites. The increase in the diffusivities with the loading is assumed to be caused by the repulsive interactions between the molecules adsorbed in the channel intersections and the adjacent straight channel. The apparent activation energy of diffusion was measured to be independent of the partial pressure of alkane, while the jump frequency increased. In HZSM-5 zeolite the apparent activation energy decreased with the partial pressure due to stronger interactions between n-hexane and the acid sites at low pressures. [Copyright &y& Elsevier]