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.
A brominated supported Ru catalyst was developed for the cleavage of C−O linkages in aryl ethers (reaching yield 90.3 % to monoaromatics from diphenyl ether) in lignin compounds without hydrogenation of the aromatic rings. Both selective poisoning of terrace sites and electronic promotion of defect sites contribute to the catalytic performance.
The reaction rates and selectivity of many metal-catalyzed reactions depend on the size of the metal particles in the nanoscale range. Primary amines are important platform molecules in the chemical ...industry. In this work, the catalytic performance of nonsupported Ru nanoparticles with sizes from 2 to 9 nm was investigated in direct amination of octanol and other alcohols into primary amines in the presence of ammonia. The 90% selectivity to octylamine was obtained over small Ru nanoparticles (d = 2 nm) even at 92% conversion, whereas for larger Ru nonsupported and supported nanoparticles, the octylamine selectivity dropped as the octanol conversion approached 70–80%. The primary reaction of alcohol amination into octylamine was found to be nearly a structure-insensitive reaction. The selectivity to primary amine drops over large Ru particles at higher conversions, because of the secondary highly structure-sensitive reaction of amine self-coupling. Over small metal nanoparticles, amine self-coupling is hindered, because of suppression of secondary imine hydrogenation. Similar structure sensitivities of the reactions involved in alcohol amination were observed for different substrates.
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 CH4 and CO at room temperature using water as the sole external oxygen source. The optimized photocatalyst consists of a TiO2 support and ammonium phosphotungstic polyoxometalate (NPW) clusters anchored with isolated Pt single atoms (Pt1). 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 Pt1 sites, with the methane activation facilitated by water-derived hydroxyl radicals.
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 %).
Losing H2: Metal‐promoted oxides supported on silica are efficient catalysts for butadiene synthesis from ethanol. The metal promoters allow ethanol dehydrogenation, the metal oxide components are efficient in acetaldehyde condensation and reduction of crotonaldehyde with ethanol, whereas the silica support allows the dehydration steps. The optimized catalyst provides 74 mol % selectivity to butadiene at 88 % ethanol conversion at 593 K.
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.
Catalyst design: A decrease in the ZSM‐5 crystallization temperature led to a decrease in the strength of acid sites with increased selectivity to propylene in methanol to olefins (MTO) (see figure).
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•Iron species in silica-supported catalysts as a function of pore diameter.•Larger iron nanoparticles are located in larger pore catalysts.•Fischer–Tropsch performance is attributed ...to Hägg iron carbide.•Extent of iron carbidization depends on iron particle size and pore diameter.•Better catalytic performance is observed on larger pore catalysts.
This paper addresses the effect of support pore sizes on the structure and performance of iron catalysts supported by mesoporous silicas in high-temperature Fischer–Tropsch synthesis. A combination of characterization techniques showed that the size of supported iron particles was controlled by catalyst pore sizes. The larger iron particles were localized in large-pore supports.
Iron carbidization with carbon monoxide resulted in preferential formation of Hägg iron carbide (χ-Fe5C2). Larger iron oxide crystallites in large-pore supports were much easier to carbidize than smaller iron oxide counterparts in small-pore supports. The catalytic performance in Fischer–Tropsch synthesis was attributed to iron carbide. Higher Fischer–Tropsch reaction rates, higher olefin, and C5+ selectivity were observed over larger pore iron catalysts. High dispersion of iron oxide in small-pore silicas was not favorable for carbon monoxide hydrogenation because of poor iron carbidization.
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