Journal of Catalysis最新文献

Acid–base bifunctional catalysts have been extensively used for a series of CC bond formation reactions. Among these catalysts, organic acid–base catalysts have attracted wide attention due to their structural variety, conformational dynamics, and enantioselectivity. To prevent mutual deactivation, a simple, effective, and versatile strategy is the attachment of both acid and base onto the surfaces of supports. In particular, the co-immobilization of organic acids and bases not only enhances synergistic effects in cooperative catalysis but also improves yields to desired products by controlling the diffusion of intermediates in tandem catalysis, leading to significant improvements in energy and atom efficiency. In this review, we highlight recent works addressing the broad topic of the co-immobilization of organic acids and bases for cooperative and tandem catalysis. We mainly focus on the synthetic strategies for silica-supported organic acid–base catalysts and polymer-supported organic acid–base catalysts. Furthermore, we summarize and discuss the structure–activity relationships of these catalysts. Last, the remaining issues and prospects will be discussed to advance the rational design and engineering of co-immobilized acid–base bifunctional catalysts.

The construction of Z-scheme charge transfer pathways simulating natural photosynthesis is considered a promising method for improving reaction driving forces. Here, we modified the surface of titanium doped Fe₂O₃ (Ti-Fe₂O₃) nanorods with NH₂-MIL-125(Ti) (Ti-MOFs) and a promising organic-inorganic hybrid Z-scheme NH₂-MIL-125(Ti)/Ti-Fe₂O₃ was successfully prepared. At 1.23 V vs. RHE, the photocurrent density of the composite photoanode reaches 2.67 mA/cm², which is 5 times higher than that of Ti-Fe₂O₃. The results of surface photovoltage, ESR and fs-TAS indicate that this improvement is mainly due to the effective Z-scheme charge transfer mechanism providing a strong driving force for charge separation and transport, greatly suppressing carrier recombination and allowing carriers with strong oxidation ability to participate in water oxidation. Meanwhile, NH₂-MIL-125(Ti) can enhance light absorption and reduce the surface defect state of Ti-Fe₂O₃. This study not only provides a feasible approach for the photoanode water splitting of traditional inorganic semiconductor/MOF based heterostructures, but also provides rich and effective means for revealing Z-scheme charge transfer mechanism in depth.

Modeling hydrogen evolution reaction (HER) activity probability on IrPdPtRhRu(1 1 1) high-entropy alloys. Determining hydrogen coverages based on ligand effects and generalized hydrogen–hydrogen repulsion.

The rate of H₂ formation is highly impacted by the level of hydrogen coverage on the catalyst surface. In search of optimal catalytic properties high-entropy alloys (HEA) are promising candidates that utilize the compositional space of multiple elements. Based on simulations of HEA model (1 1 1) surfaces with a range of hydrogen coverages, distributions of binding energies are used to construct a framework that approximates the probability that adsorbed hydrogen may lead to the formation of H₂ as a function of applied potential. By optimizing the alloy compositions for the highest activity probability at given potentials the best and most efficient catalyst candidates for HER can be identified. Treating hydrogen–hydrogen repulsion effects and binding energy separately, we find that the repulsion is larger for HEAs than for pure metals. Differing isotherm slopes in the mean adsorption and desorption energies demonstrate a possible hysteresis for hydrogen adsorption on HEAs.

The rational design of a step-scheme (S-scheme) heterojunction with strong internal electric field (IEF) and high redox capacity is a promising strategy for photocatalytic CO₂ reduction reaction (CO₂RR). However, the precise process of charge transport on the multi-interfaces remains a great challenge. Herein, a dual S-scheme heterojunction constructed in the ZnO@Co₃O₄/CsPbBr₃ hierarchical nanocage was prepared for enhancing CO₂RR activity. Without sacrificial agent and photosensitizer, the optimal photocatalyst exhibits a competitive CH₄ yield rate of 238.8 μmol g⁻¹h⁻¹ with high selectivity (90.9%), affording an apparent quantum efficiency of 4.6 % at 400 nm, outperforming most previously comparable photocatalysts. In situ X-ray photoelectron spectroscopy (in situ XPS), photoelectrochemical measurement and theoretical calculation verifies the dual S-schematic charge-transport pathway. The remarkably improved performance in CO₂RR is due to the rapid charge separation through O-Co-Br bridge driven by the strong internal electric field. This research furnishes a new insight to reveal dynamic charge transfer mechanism for CO₂ conversion applications.

In this study, we explore the potential of metal–organic frameworks (MOFs) as catalysts for converting CO₂ into valuable chemicals. The focus is on integrating frustrated Lewis pairs (FLPs) within the UiO−67 framework. We investigated 12 distinct functionalized FLP moieties (X =  −BF₂, −BCl₂, −BBr₂, −BH₂, −B(CH₃)₂, −B(CF₃)₂, −B(CN)₂, −B(NO₂)₂, −B(OH)₂, −B(NH₂)₂, −B(OCH₃)₂, and −B(N(CH₃)₂)₂ to determine their ability to activate small molecules within heterogeneous catalysis using density functional theory (DFT). This study reveals two critical stages in the CO₂ conversion process with H₂ in UiO−67−X. First, the initial heterolytic cleavage of H₂ at the FLP site, and second, the subsequent hydrogenation of CO₂. The latter involves the addition of a hydride and a proton. Our findings demonstrate that these modifications facilitate efficient dissociation of H₂ into H^δ− and H^δ+ with energy barriers ranging from 0.12 to 0.87 eV and CO₂ hydrogenation barriers spanning from 0.61 to 1.90 eV. Notably, the −B(CH₃)₂ functional group exhibited superior effectiveness in CO₂ hydrogenation to formic acid (HCOOH; FA). This enhanced activity correlates directly with FLP acidity and the Gibbs free energy changes in H₂ dissociation reaction. It highlights the significant influence of FLP−assisted heterolytic dissociation of H₂ in the CO₂ conversion process. The results of this study do more than introduce metal-free heterogeneous FLPs within MOFs. They also establish a clear link between the functional group composition, FLP acidity, and catalytic efficiency. These insights offer a valuable theoretical foundation for the design of advanced UiO−67−X catalysts. They open up possibilities for transforming greenhouse gases into valuable chemical products, contributing to sustainable chemical synthesis.

Chemoselective synthesis allows for the generation of diverse products from identical starting materials, which is a significant strategy to build molecular diversity rapidly. By employing acceptorless dehydrogenation and borrowing hydrogen strategies, we herein report a cobalt-catalyzed chemoselective C(sp³)–H bond functionalization of methyl heteroarenes, the alkenylation and alkylation products are obtained using alcohol as the coupling partner under different reaction conditions. The scopes of both arenes and alcohols, synthetic applications, preliminary mechanistic studies, and a proposed mechanism were presented.

α-(Silyl)acetates are a class of stable and versatile organosilicon compounds wherein the inherent diversity of silicon can be exploited to unlock reactivity through masked carbanions, carbon nucleophiles, carbon-centered radical intermediates, and silicon electrophiles. Hence the developing of new methodology for their preparation is important and attractive. Herein, we developed an efficient method for the carbonylative synthesis of versatile α-(silyl)acetates. The reaction features simple operation, mild conditions, broad substrate scope, and good functional group tolerance. The α-(silyl)acetates prepared showed excellent reactivity in a series of transformations, highlighting the synthetic utility of this strategy.

Controllable synthesis of organic–inorganic hybrid materials with functional sites and tunable structures is of great significance. Herein, novel melamine-based G_n-Dendron-OMS (G represents Generation; n = 1, 2, 3; Dendron = DMEDA, PIP, AMP, TMDP; OMS = FDU-12, MCM-41, SBA-15, KIT-6) hybrids with various terminal diamine groups, Dendron generations and ordered mesoporous silica hosts were synthesized, characterized and used to catalyze the nitroaldol (Henry) reaction. Among these hybrids, G₁-DMEDA-FDU-12 shows outstanding catalytic performance with 4-nitrobenzaldehyde conversion of 96 %, β-nitroalcohol selectivity of 94 % and TOF of 20.4 h⁻¹ under mild and solvent-free conditions. HMDS and HCl intervening active-site deactivation, in situ Raman spectra, Mulliken charge distribution and DFT calculations suggest that the triazine N atom (N_T) in the Dendron chain functions as the active site, the dehydrogenation of nitromethane is the rate determining step (RDS) and the Gibbs free energy change of the RDS on the triazine N atom decreased to as low as 30.2 kcal mol⁻¹. The formation of the deuterated β-nitroalcohol (R-OD) detected by FTIR and NMR indicates that nitroaldol (Henry) reaction undergoes an ion-pair mechanism. This work for the first time reveals the triazine-based active site for the nitroaldol (Henry) reaction and highlights a novel strategy to construct uniform, functional and tunable active sites for potential applications in catalysis, CO₂ capture and pollutant removal.

Steam reforming is a promising approach to remove biomass gasification tar impurities. Noble metal promotion (Pt/Pd/Rh), Ni+Co loading (20–40 wt%) and calcination temperature (600–800 °C) effects were investigated with hydrotalcite-derived Ni-Co/Mg(Al)O catalysts for bio-syngas tar steam reforming. Fresh catalysts were characterized by XRD, ICP-MS, XRF, N₂-physisorption, H₂-chemisorption and TPR. Small-diameter metal particles were achieved (5.1–5.8 nm) below a Ni+Co loading threshold (above 30 wt%). Model bio-syngas activity tests were performed (CH₄/H₂/CO/CO₂ molar ratio = 10/35/25/25, 700 °C, steam-to-carbon = 3.0) with and without tar addition (toluene/1-methylenaphthalene, 10 g/Nm³). Tar elimination was achieved with all samples. Enhanced reforming activity accompanied by strong tar active site inhibition effects were found for the Rh promoted catalyst. Noble metal promoted samples were effectively reduced in the bio-syngas environment (H₂/CO/CH₄) without any pre-reduction (in situ activation by the action of the syngas) with Rh > Pt > Pd. Coke characterization was conducted with TPO-MS and Raman spectroscopy. High-dispersion 20NiCo/30NiCo samples were strongly deactivated through active site inhibition and coke formation. High-temperature calcination (800 °C) reduced the deactivation effects of the coke deposition, attributed to enhanced Mg(Al)O-assisted coke gasification.

One of the most important scientific challenges of the time is to design catalysts that produce H₂ from “minimum ${\mathrm{CO}}_2$” sources. One way to do this is by aqueous phase reforming (APR) of sugar alcohol molecules derived from biomass. However, to date, H₂ yields have been disappointing, indicating a need to optimize catalysts and reaction conditions to improve H₂ production. This requires a detailed understanding of the APR mechanism. There are three primary steps: dehydrogenation, decarbonylation, and water gas shift. However, the details of these steps remain unknown due to the large and complex structures of the reactant molecules, the aqueous reaction conditions, and the participation of multiple types of active sites in the mechanism. To begin to address these knowledge gaps, herein we study the effect of liquid $H_{2}O$ solvent and multiple types of active sites on the mechanism of CH₃OH dehydrogenation. Specifically, we use a combination of multiscale modeling, microkinetic modeling, and Fourier transform infrared spectroscopy to determine the mechanism of CH₃OH dehydrogenation on Pt/Al₂O₃ catalysts. We investigate sites on the terraces of large Pt particles as well as sites at the Pt/Al₂O₃ perimeter and the influence of liquid $H_{2}O$ on both. We show that the reaction is predominantly carried out on terrace sites due to inhibition by strongly bound $H_{2}O$ molecules at perimeter sites. We further show that water plays a significant role in the CH₃OH dehydrogenation mechanism on Pt terrace sites but that these changes do not influence the observed rate of CH₃OH consumption.