Applied Catalysis A: General最新文献

The catalytic dehydrations of methanol and n-butanol on strongly acidic solids have been tested in two types of microreactors in the gas phase between 80 – 240 ºC. For the methanol transformation to dimethyl ether, the conversion was evaluated in situ with an innovative use of the FTIR spectroscopy in batch microreactor. The same catalysts were used for the conversion of n-butanol to butenes and n-butyl-ether under similar conditions, determined using a flow microreactor with the conventional gas chromatography downstream analysis. The catalysts included the Wells-Dawson type heteropolyacids, H₆P₂W₁₈O₆₂ and H₆P₂Mo₁₈O₆₂, supported on TiO₂ and/or BN. The activity orders obtained in those methods were compared to that obtained by the ammonia sorption using the gas-flow through microcalorimeter at 150 ºC. The significant effect of TiO₂ and BN supports in the methanol and butanol dehydrations makes the TiO₂ and BN-supported Well-Dawson type heteropolyacids potentially relevant for industrial transformations of biomass derived feedstock.

Metal oxide catalysts like ceria-supported vanadia (VO_x/Ce_1-xZr_xO₂) with different Zr contents were prepared by coupling ceria-zirconia solid solution and vanadia. Characterization revealed that the insertion of zirconia into ceria significantly improved catalytic activity due to the generation of more oxygen vacancies and distortion of the composite structure. The oxygen vacancy concentration initially increased with the increase of Zr (x= wt%) and peaked at x=0.7 and then decreased. The reliance of oxygen vacancy concentration in VO_x/Ce_1-xZr_xO₂ catalyst on their catalytic activity in methanol oxydehydrogenation was further investigated. Results indicated that oxygen vacancies not only activated oxygen species but also cleaved C–H bonds alongside V⁵⁺ active site contained terminal oxygen atoms for cleaving O–H and C–H bonds within the adsorbed methanol. The VO_x/Ce_0.3Zr_0.7O₂ exhibited the best catalytic activity with the methanol conversion of 76 % and the dimethoxymethane selectivity of 96 % at 200 ℃ and atmospheric pressure in a fixed-bed reactor.

In order to improve poor charge carrier transport properties of p-type oxide semiconductors, the post thermal treatment under oxygen atmosphere is systematically studied as a defect engineering strategy for LaFeO₃ photocathodes. The post-thermal oxidation process significantly decreases the photo-generated charge recombination and promotes the charge transport properties of LaFeO₃ photocathodes. The density functional theory calculations and experimental analyses indicate that the thermal oxygen treatment can promote the formation of La vacancy and the reduction of the oxygen vacancy in LaFeO₃, which facilitates its bulk charge transport by increasing hole carrier density. The optimized LaFeO₃ photocathode yields an O₂ reduction photocurrent density of −313 µA/cm² at 0.6 V vs RHE in O₂-saturated KOH solution under 1 sun irradiation. Additionally, we also investigated the feasibility of photoreduction of water by using a Pt-deposited LaFeO₃ photocathodes.

We show the applicability of a preparation method, previously reported for obtaining tailored bulk VC_x catalysts, for alumina-supported G5TMCs. The characteristics of the G5TMCs/Al₂O₃ catalysts and their behaviour in the selective reduction of CO₂ to CO through the RWGS reaction is reported. VC_x/Al₂O₃ catalysts were active, stable and highly selective; meanwhile NbC/Al₂O₃ and TaC/Al₂O₃ were not active. VC_x/Al₂O₃ catalysts exhibited selectivity to CO over 99.5 % at temperature above 773 K. The characteristics of alumina-supported vanadium carbide particles depended on the vanadium precursor and on the atmosphere used during the catalyst preparation. XPS characterization of VC_x/Al₂O₃ catalysts revealed the presence of carbide species on surface before and after RWGS reaction. The catalytic behaviour of VC_x/Al₂O₃ is analysed in the light of their characteristics and compared with bulk VC_x counterparts. The most performant catalyst, VC(Pr)/Al₂O_3, was stable over 4 days at 723 K, with ∼100 % selectivity to CO and CO₂ conversion of ∼11 %.

A core-shell structured catalyst 3Ni-7Co@SiO₂-0.2 was created to facilitate the reductive amination of pyruvic acid into alanine and the yield of alanine is up to 99 %. The SiO₂ shell played a crucial role in spatial isolation effect, preventing the direct hydrogenation of pyruvic acid and improving the selectivity of alanine. By inter-doping Ni and Co, the electronic structure and properties are adjusted, the d-band center is reduced which is beneficial to the desorption of the product and the reaction barrier is reduced. Furthermore, it is proposed that catalysts exhibit better reductive amination reaction performance when there is a smaller difference in adsorption energy between NH₃ and H₂ atoms on the metal surface.

Small-molecule aldehydes are promising additives to regulate product distribution in methanol-to-hydrocarbon (MTH) reaction. Herein, the co-feeding of C₁-C₄ aldehydes with methanol resulted in a significant increase in aromatic formation with the order: acetaldehyde > formaldehyde > propanal ≈ butanal. The mechanistic basis for this enhancement in aromatic production derived from both a direct participation pathway of aldehydes and an indirect pathway via driving the aromatic-based cycle. C₂₊ aldehydes could undergo multiple aldol-condensation on Brønsted acid sites to form larger alkenals, followed by sequential cyclization-dehydration reaction to cycloalkenes or aromatic species. The Prins reaction could be extended to all C₁-C₄ aldehydes with alkenes by generating the corresponding dienes. The hydrogen transfer from methanol to C₂₊ aldehydes produced C₂₊ olefins and formaldehyde, which would lead to extra formaldehyde-mediated aromatic formation pathway. The intricate evolution pathway of C₁-C₄ aldehydes in MTH reaction was constructed by detecting abundant oxygenate and hydrocarbon intermediates.

Bioethanol, a renewable resource, can be converted into high value-added chemicals. Methylbenzyl alcohol in its ortho- and para-isomers has been successfully synthesized from ethanol upgrading over metal-modified hydroxyapatite (HAP). However, meta-methylbenzyl alcohol (3-MB-OH), a particularly valuable fine chemical, has yet to be produced from ethanol. Herein, we present a novel reaction pathway for the selective synthesis of 3-MB-OH over HAP by co-feeding ethanol with methacrolein. Notably, the selectivity of 3-MB-OH reached up to 36.2 % in our tests. Experiments using intermediates as reactants proved that the introduction of methacrolein definitively led to the production of 3-MB-OH, which was also confirmed by in-situ diffuse reflectance infrared Fourier-transform spectroscopy. Moreover, we inferred the co-conversion reaction pathway of ethanol and methacrolein. Density functional theory calculations indicated that ethanol preferentially underwent Meerwein-Ponndorf-Verley hydrogen transfer with methacrolein, resulting in acetaldehyde formation and subsequently promoting the synthesis of aromatic compounds.

The photo-Fenton technology is widely used in wastewater treatment due to its high efficiency in photodegrading organic pollutants. In this study, FeOOH quantum dots (FQDs) were utilized as surface modifiers anchored on the surface of BiOCl nanoplates (BnPs), resulting in FQDs@BnPs3 with exposed (001) crystal plane. Surface engineering resolves material aggregation and boosts photocarrier separation rate. FQDs@BnPs3 exhibit high sensitivity to visible light in the system, displaying excellent photocatalytic activity and stability in the removal of dyes and antibiotics. The removal efficiency of tetracycline exceeds 90 % within 15 min and remains highly active after 10 cycles. It had a wide range of acid-base applicability. Through free radical trapping experiments, ·OH was identified as the primary active species in the reaction. By analyzing the degradation pathway, the mechanism of the catalyst is proposed. Summarized, quantum dots combined with semiconductor material offer a new strategy for effective degrading organic pollutants.

Zinc oxide (ZnO) is commonly used as a promoter in Cu-based catalysts for the Rochow-Müller reaction, which is used to produce organosilane monomers in the organosilicon industry. However, the impact of ZnO on the phase transformation of Cu-based catalysts during the Rochow-Müller reaction has not been fully revealed. In this work, we synthesized two ZnO-modified Cu₂O model catalysts by simple ball milling (Cu₂O-ZnO) and physical mixing (Cu₂O+ZnO) methods. The addition of ZnO enhanced catalytic properties, resulting in higher dimethyldichlorosilane (M2) selectivity and Si conversion compared to using the pure Cu₂O catalyst. The introduction of ZnO into Cu₂O enhanced the adsorption of methyl chloride (MeCl) on the Cu₂O surface, causing Cu₂O to transform into Cu and CuCl. Subsequently, CuCl reacted with active Si to form active Cu_xSi species. This work provides valuable insights into the roles of ZnO in Cu₂O-based catalysts and sheds light on their catalytic mechanism in the Rochow-Müller reaction.

The impact of two-dimensional Mo₂C (2D-Mo₂C) on the activity and stability of a Ni/γ-Al₂O₃ catalyst for the dry reforming of methane (DRM) is reported. 1.1 wt% 2D-Mo₂C added to 13 wt% Ni/γ-Al₂O₃ increased activity by ∼40 %. Characterization results showed an interaction between 2D-Mo₂C and Ni that resulted in the formation of a Ni_xMo_y bulk phase (XRD) and Ni-Mo-oxycarbide surface species (XPS). The presence of 2D-Mo₂C also improved the stability of the catalyst compared to Ni/γ-Al₂O₃ by reducing coke deposition. H₂ space-time-yields (STYs) were independent of CO₂ partial pressure and were lower than the CO STYs. Power law kinetic models were consistent with a DRM reaction pathway via CH₄ decomposition (MD) and the reverse Boudouard (RBD) reactions.