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The cleavage of C−O linkages in aryl ethers in biomass‐derived lignin compounds without hydrogenation of the aromatic rings is a major challenge for the production of sustainable mono‐aromatics. Conventional strategies over the heterogeneous metal catalysts require the addition of homogeneous base additives causing environmental problems. Herein, we propose a heterogeneous Ru/C catalyst modified by Br atoms for the selective direct cleavage of C−O bonds in diphenyl ether without hydrogenation of aromatic rings reaching the yield of benzene and phenol as high as 90.3 % and increased selectivity to mono‐aromatics (97.3 vs. 46.2 % for initial Ru) during depolymerization of lignin. Characterization of the catalyst indicates selective poisoning by Br of terrace sites over Ru nanoparticles, which are active in the hydrogenation of aromatic rings, while the defect sites on the edges and corners remain available and provide higher intrinsic activity in the C−O bond cleavage. [ABSTRACT FROM AUTHOR]

The nanostructure of a semiconductor is a crucial parameter for efficient photocatalytic performance. Hereby, we have synthesized monoclinic bismuth vanadate (BiVO4) crystals with controlled ratio of {010} and {110} facets. The selective deposition of CuOx and CoOx over {010} and {110} facets has been performed using photo‐reduction and photo‐oxidation methods, respectively. It resulted in a highly efficient charge separation of photogenerated electrons and holes and enhancement of the photocatalytic reduction of CO2 by H2O into hydrocarbons, including CH4, C2H6 and C3H8. The controlled co‐catalyst deposition over different semiconductor facets provides a strategy for the synthesis of hydrocarbons from CO2 and H2O by efficient charge separation. [ABSTRACT FROM AUTHOR]

Cobalt distribution between the external surface and micropores and acidity of the large pore BEA zeolite were controlled by choosing the sequence of impregnation and ion exchange procedures. Higher concentration of ion exchangeable cobalt was observed in the catalyst prepared by ion‐exchange of the zeolite proton form. The presence of Na+ instead of H+ ions in the exchange positions of zeolite favored deposition of cobalt on the external surface. The acid sites in the zeolite micropores can be then restored by subsequent ion exchange of sodium with ammonium nitrate and calcination. The catalytic performance of the cobalt zeolite catalysts prepared using different impregnation and ion exchange procedures was tested in the Fischer‐Tropsch synthesis. Higher reaction rates were observed over the catalysts, which did not contain cobalt ions in the cation sites of the zeolite. Lower methane selectivity, higher selectivity to long chain hydrocarbons and high fraction of isomerized products are observed when cobalt species are located on the zeolite outer surface and acid sites inside the BEA zeolite micropores. Ion launch sequence: Impregnation and ion exchange sequences control metal localization, acidity, diffusion and performance of cobalt‐BEA catalysts for Fischer‐Tropsch synthesis [ABSTRACT FROM AUTHOR]

Abstract: A series of nanosized ZSM‐5 samples was synthesized at 170, 150, 120, and 100 °C. Experimental data show that the decrease of crystallization temperature leads to significant changes in zeolite properties. Crystals synthesized at 100 °C exhibit many framework defects with lower acid‐site density, strength, and a larger external surface area. The selectivity to light olefins and the propylene‐to‐ethylene ratio increases as the crystallization temperature decreases. A propylene‐to‐ethylene ratio of above 6 with the highest selectivity to propylene of 53 % was obtained over ZSM‐5 catalyst prepared at 100 °C. The stability of the nanosized zeolite in methanol to olefins (MTO) was also improved compared to the industrial sample with a similar Si/Al ratio. This catalytic performance is a result of the decrease in the acid‐site density, strength, and the crystals’ size, providing a shorter diffusion path and larger external surface area. The presence of structural defects and a different external surface in the crystals has been shown to play an important role in the MTO catalyst performance. [ABSTRACT FROM AUTHOR]

This paper focuses on the effect of synthesis conditions on the structure of cobalt-ZSM-5 zeolites and the localization, dispersion, and reducibility of cobalt species and their catalytic performance in Fischer-Tropsch synthesis. The zeolite catalysts were prepared by using carbon nanotubes as sacrificial templates. Addition of pristine carbon nanotubes resulted only in a slight increase in the zeolite mesoporosity, whereas the presence of carbon nanotubes impregnated with cobalt drastically modified the zeolite morphology and texture. The zeolite mesoporous volume increased by 3-4 times. The catalysts prepared by using cobalt-impregnated carbon nanotubes as templates showed 5-8 times higher Fischer-Tropsch reaction rates normalized by reducible cobalt compared with the catalysts prepared by conventional impregnation. Higher selectivity to isomerized branched hydrocarbons on these zeolites was attributed to the enhanced diffusion favoring removal of isomerized products and avoiding their cracking. [ABSTRACT FROM AUTHOR]

2,5-furandialdehyde (DFF) was synthesized by electrogenerative oxidation of 5-hydroxymethylfurfural (HMF) over a PtRu catalyst with 89% selectivity at 508C after 17 h. This approach opens an avenue for a selective, energy-efficient and green oxidation of biomass-derived platform alcohols to added-value chemicals. [ABSTRACT FROM AUTHOR]

Syngas is an important intermediate for the synthesis of chemicals and fuels; it can be produced from renewable and fossil feedstocks. Syngas conversion on Fe catalysts results mostly in linear paraffins, olefins, and oxygenates. In the produced olefins or oxygenates, the functional groups or double bonds are always located in the hydrocarbon α-position. The yield of nonlinear functionalized hydrocarbons or chemical compounds with secondary and tertiary functional groups is low. In this paper direct synthesis of diverse functionalized and branched hydrocarbons in the Fischer-Tropsch reaction is explored by the cofeeding aldehydes to syngas; the added aldehydes initiate surface polymerization. Quantitative stoichiometric incorporation of aldehydes in the growing hydrocarbon chain was observed. The hydrocarbons that contain incorporated aldehyde fragments exhibit an Anderson-Schulz-Flory distribution similar to that from conventional Fischer-Tropsch synthesis. [ABSTRACT FROM AUTHOR]

This study focuses on the effects of the localization of Co species, zeolite structure, and acidity on the performance of Co bifunctional catalysts promoted with Pt for the direct synthesis of iso-paraffins from syngas. ZSM-5, MOR, and BEA were chosen as zeolites with different structures and pore diameters. The catalysts were prepared either by incipient wetness impregnation or by the mechanical mixing of the zeolite with a conventional silica-supported Co catalyst. The increase in the pore size and open character of the zeolite structure from ZSM-5 to BEA resulted in a higher fraction of Co located inside the pores of the catalysts prepared by impregnation. The catalytic performance was affected strongly by the zeolite acidity, pore structure, and Co distribution between the pores and the external surface. The selectivity to short-chain iso-paraffins is affected principally by the zeolite acidity, whereas the selectivity to long-chain branched hydrocarbons mostly depends on steric effects. [ABSTRACT FROM AUTHOR]

Direct synthesis represents a green alternative, an environmentally benign process for the production of hydrogen peroxide. This is a three-phase reaction, a solid catalyst with gas reactants and a liquid phase, which collects hydrogen peroxide formed from the catalyst surface. The choice of solvent and/or addition of promoters has a significant effect on the reaction rates observed, as well as selectivity towards peroxide. In addition to non-toxic water, short chain alcohols are very attractive, due to good solubility of reacting gases. Here we report an extensive study on the influence of different groups of solvents on the direct synthesis reaction when either applied alone or as co-solvent under non-explosive and conventionally explosive reaction conditions. [ABSTRACT FROM AUTHOR]

The synthesis of buta-1,3-diene from ethanol has been studied over metal-containing (M = Ag, Cu, Ni) oxide catalysts (MOx = MgO, ZrO2, Nb2O5, TiO2, Al2O3) supported on silica. Kinetic study of a wide range of ethanol conversions (2-90%) allowed the main reaction pathways leading to butadiene and byproducts to be determined. The key reaction steps of butadiene synthesis were found to involve ethanol dehydrogenation, acetaldehyde condensation, and the reduction of crotonaldehyde with ethanol into crotyl alcohol. Catalyst design included the selection of active components for each key reaction step and merging of these components into multifunctional catalysts and adjusting the catalyst functions to achieve the highest selectivity. The best catalytic performance was achieved over the Ag/ZrO2/SiO2 catalyst, which showed the highest selectivity towards butadiene (74 mol%). [ABSTRACT FROM AUTHOR]

A help rather than a hindrance: Carbonaceous deposits have been found to play a key role in the selective synthesis of isoprene from formaldehyde and isobutene over solid catalysts. They accumulate on the catalyst surface during the induction period and promote the interaction of the substrates at the steady state. The proposed mechanism (see scheme) shows the way forward for the design of efficient solid catalysts for the synthesis of isoprene. [ABSTRACT FROM AUTHOR]

A solid acid foam-structured catalyst based on a binderless zirconium phosphate (ZrPO) coating on aluminum foam was prepared. The catalyst layer was obtained by performing a multiple washcoating procedure of ZrPO slurry on the anodized aluminum foam. The effect of the pretreatment of ZrPO, the concentration of the slurry, and the amount of coating on the properties of the foam was studied. The catalytic properties of the prepared foams have been evaluated in the dehydration of glucose to 5-hydroxymethylfurfural (HMF) in a biphasic reactor. The catalytic behavior of ZrPO foam-based catalysts was studied in a rotating foam reactor and compared with that of bulk ZrPO. The effect of a silylation procedure on the selectivity of the process was shown over bulk and foam catalysts. This treatment resulted in a higher selectivity due to the deactivation of unselective Lewis acid sites. Addition of methylisobutylketone leads to extraction of HMF from the aqueous phase and stabilization of the selectivity to HMF over bulk ZrPO. A more intensive contact of the foam with the aqueous and organic phases leads to an increase in the selectivity and resistance to deactivation of the foam in comparison with a bulk catalyst. [ABSTRACT FROM AUTHOR]

Different acidic heterogeneous catalysts like alumina, aluminosilicate, zirconium phosphate, niobic acid, ion-exchange resin Amberlyst-15, and zeolite MOR have been studied in fructose dehydration to 5-hydroxymethylfurfural (HMF). The acidity of these materials was characterized using temperature-programmed desorption of NH3 and IR spectroscopy of adsorbed pyridine. The nature and strength of acid sites was shown to play a crucial role in the selectivity towards HMF. Brønsted acid sites in the case of zeolites and ion-exchange resin led to high selectivities in the dehydration of fructose with an increase in selectivity with the addition of an organic phase. Lewis acidity in the case of phosphate and oxides resulted in the intensive production of humins from fructose at the initial stages of the process, whereas organic phase addition did not affect selectivity. [ABSTRACT FROM AUTHOR]

The electrophoretic deposition method has been applied for the formation of an amorphous zirconium phosphate layer on the surface of open-cell aluminum foam. The aluminum foam was fully and uniformly covered by the zirconium phosphate layer with a good mechanical adherence to the support. The obtained composites were characterized by using XRD, SEM and nitrogen adsorption. The coated aluminum foams showed high catalytic activity in the dehydration of fructose to 5-hydroxymethylfurfural. This method of foam coating is much more convenient and effective than the traditional washcoating procedure, avoiding the anodization pretreatment of the foam to increase adherence. [ABSTRACT FROM AUTHOR]