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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]

A one-step process for the selective production of methane from low-value aqueous carbohydrate streams is proposed. Sorbitol, used herein as a model compound, is fully converted to methane, CO2, and a minor amount of H2 by using a physical mixture of Pt and Ru (1:5 in mass basis) at 220 °C and 35 bar. This conversion is the result of hydrogenolysis of part of the sorbitol over Ru and the in situ production of H2 through the aqueous-phase reforming of the remaining carbohydrate over Pt. A synergistic effect of the combination of these two catalysts results in the rapid and highly selective conversion of the carbohydrate to methane. This process offers the possibility of upgrading a low-value carbohydrate stream into a valuable fuel with no addition of H2. Exergy analysis reveals that nearly 80 % of the exergy of the reactant is recovered as methane. [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]

Effective conversion of methane to a mixture of more valuable hydrocarbons and hydrogen under mild conditions is a great scientific and practical challenge. Here, we synthesized Zn-containing nanosized MFI zeolite for direct oxidation of methane in the presence of H2O and air. The presence of the surface hydroxyl groups on nanosized MFI-type zeolite and their significant reduction in the Zn-containing nanosized MFI zeolite were confirmed with Infrared Fourier Transform (FTIR) spectroscopy. Incorporation of zinc atoms into the framework of nanosized MFI zeolite is revealed by Nuclear Magnetic Resonance, X-ray Diffraction a UV-Vis Spectroscopy. Unexpectedly, pure silica MFI zeolite exhibited the highest photocatalytic performance. Our finds demonstrated that large number of isolated silanol groups and silanol nests increase the formation of •OH, and enhance the productivity of oxygenate compounds and C2H6, while the Zn incorporated into the zeolite framework or attached to the silanol nests of the nanosized zeolites are less efficient. A mechanism of photocatalytic methane oxidation is proposed. These findings provide insights into developing active nanosized zeolite photocatalysts with extended amount of surface hydroxyl groups that can play a key role in photocatalytic methane conversion., (© 2024 Wiley‐VCH GmbH.)

Among semiconductor nanomaterials, titanium dioxide is at the forefront of heterogeneous photocatalysis, but its catalytic activity greatly suffers from the loss of photoexcited charge carriers through deleterious recombination processes. Here, we investigate the impact of an external electric field (EEF) applied to conventional P25 TiO 2 nanopowder with or without Au nanoparticles (NPs) to circumvent this issue. The study of two redox reactions in the gas phase, water splitting and toluene degradation, reveals an enhancement of the photocatalytic activity with rather modest electric fields of a few volt/centimeters only. Such an improvement arises from the electric-field-induced quenching of the green emission in anatase, allowing the photoexcited charge carriers to be transferred to the adsorbed reactants instead of pointless radiative recombinations. Applying an EEF across a trap-rich metal oxide material, such as TiO 2 , which, when impregnated with Au NPs, leads, respectively, to 12- and 6-fold enhancements in the production of hydrogen and the oxidation of toluene for an electric field of 8 V/cm, without any electrolysis, is a simple and elegant strategy to meet higher photocatalytic efficiencies.

Methanol-to-hydrocarbons (MTH) process has been considered one of the most practical approaches for producing value-added products from methanol. However, the commonly used zeolite catalysts suffer from rapid deactivation due to coke deposition and require regular regeneration treatments. We demonstrate that low-melting-point metals, such as Ga, can effectively promote more stable methanol conversion in the MTH process by slowing coke deposition and facilitating the desorption of carbonaceous species from the zeolite. The ZSM-5 zeolite physically mixed with liquid gallium exhibited an enhanced lifetime in the MTH reaction, which increased by a factor of up to ~14 as compared to the parent ZSM-5. These results suggest an alternative route to the design and preparation of deactivation-resistant zeolite catalysts., (© 2024. The Author(s).)

Transformations of oxygenates (CO 2 , CO, H 2 O, etc.) via Mo 2 C-based catalysts are facilitated by the high oxophilicity of the material; however, this can lead to the formation of oxycarbides and complicate the identification of the (most) active catalyst state and active sites. In this context, the two-dimensional (2D) MXene molybdenum carbide Mo 2 C T x ( T x are passivating surface groups) contains only surface Mo sites and is therefore a highly suitable model catalyst for structure-activity studies. Here, we report that the catalytic activity of Mo 2 C T x in Fischer-Tropsch (FT) synthesis increases with a decreasing coverage of surface passivating groups (mostly O*). The in situ removal of T x species and its consequence on CO conversion is highlighted by the observation of a very pronounced activation of Mo 2 C T x (pretreated in H 2 at 400 °C) under FT conditions. This activation process is ascribed to the in situ reductive defunctionalization of T x groups reaching a catalyst state that is close to 2D-Mo 2 C (i.e., a material containing no passivating surface groups). Under steady-state FT conditions, 2D-Mo 2 C yields higher hydrocarbons (C 5+ alkanes) with 55% selectivity. Alkanes up to the kerosine range form, with value of α = 0.87, which is ca. twice higher than the α value reported for 3D-Mo 2 C catalysts. The steady-state productivity of 2D-Mo 2 C to C 5+ hydrocarbons is ca. 2 orders of magnitude higher relative to a reference β-Μo 2 C catalyst that shows no in situ activation under identical FT conditions. The passivating T x groups of Mo 2 C T x can be reductively defunctionalized also by using a higher H 2 pretreatment temperature of 500 °C. Yet, this approach leads to a removal of carbidic carbon (as methane), resulting in a 2D-Mo 2 C 1- x catalyst that converts CO to CH 4 with 61% selectivity in preference to C 5+ hydrocarbons that are formed with only 2% selectivity. Density functional theory (DFT) results attribute the observed selectivity of 2D-Mo 2 C to C 5+ alkanes to a higher energy barrier for the hydrogenation of surface alkyl species relative to the energy barriers for C-C coupling. The removal of O* is the rate-determining step in the FT reaction over 2D-Mo 2 C, and O* is favorably removed in the form of CO 2 relative to H 2 O, consistent with the observation of a high CO 2 selectivity (ca. 50%). The absence of other carbon oxygenates is explained by the energetic favoring of the direct over the hydrogen-assisted dissociative adsorption of CO., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Direct functionalization of methane selectively to value-added chemicals is still one of the main challenges in modern science. Acetic acid is an important industrial chemical produced nowadays by expensive and environmentally unfriendly carbonylation of methanol using homogeneous catalysts. Here, we report a new photocatalytic reaction route to synthesize acetic acid from CH 4 and CO at room temperature using water as the sole external oxygen source. The optimized photocatalyst consists of a TiO 2 support and ammonium phosphotungstic polyoxometalate (NPW) clusters anchored with isolated Pt single atoms (Pt 1 ). It enables a stable synthesis of 5.7 mmol·L -1 acetic acid solution in 60 h with the selectivity over 90% and 66% to acetic acid on liquid-phase and carbon basis, respectively, with the production of 99 mol of acetic acid per mol of Pt. Combined isotopic and in situ spectroscopy investigation suggests that synthesis of acetic acid proceeds via a photocatalytic oxidative carbonylation of methane over the Pt 1 sites, with the methane activation facilitated by water-derived hydroxyl radicals.

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., (© 2021 Wiley-VCH GmbH.)

In the present communication, we uncovered the aqueous phase Fischer-Tropsch reaction over rhodium catalysts. The reaction results in the synthesis and consecutive separation of hydrocarbons and oxygenates into two phases. Use of a rhodium Schiff base complex as a precursor for catalyst preparation allows efficient control of the Rh metal nanoparticle size distribution and leads to higher alcohol selectivity.

The photocatalytic conversion of CO 2 not only reduces the greenhouse effect, but also provides value-added solar fuels and chemicals. Herein, we report the design of new efficient core-shell nanocomposites for selective photocatalytic CO 2 to CO conversion, which occurs at ambient temperature. A combination of characterization techniques (TEM, STEM-EDX, XPS, XRD, FTIR photoluminescence) indicates that the CO 2 reduction occurs over zinc species highly dispersed on the heteropolyacid/titania core-shell nanocomposites. These core-shell structures create a semiconductor heterojunction, which increases charge separation and the lifetime of charge carriers' and leads to higher electron flux. In situ FTIR investigation of the reaction mechanism revealed that the reaction involved surface zinc bicarbonates as key reaction intermediates. In a series of catalysts containing noble and transition metals, zinc phosphotungstic acid-titania nanocomposites exhibit high activity reaching 50 μmol CO g -1 h -1 and selectivity (73%) in the CO 2 photocatalytic reduction to CO at ambient temperature. The competitive water splitting reaction has been significantly suppressed over the Zn sites in the presence of CO 2 ., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Chemical utilization of vast fossil and renewable feedstocks of methane remains one of the most important challenges of modern chemistry. Herein, we report direct and selective methane photocatalytic oxidation at ambient conditions into carbon monoxide, which is an important chemical intermediate and a platform molecule. The composite catalysts on the basis of zinc, tungstophosphoric acid and titania exhibit exceptional performance in this reaction, high carbon monoxide selectivity and quantum efficiency of 7.1% at 362 nm. In-situ Fourier transform infrared and X-ray photoelectron spectroscopy suggest that the catalytic performance can be attributed to zinc species highly dispersed on tungstophosphoric acid /titania, which undergo reduction and oxidation cycles during the reaction according to the Mars-van Krevelen sequence. The reaction proceeds via intermediate formation of surface methyl carbonates.

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., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)