ACS Catalysis 最新文献

Controlling the location and microenvironment of active centers in the zeolite framework is critical for understanding the in-depth structure–performance relationships of catalytic systems and constructing highly efficient catalysts. Herein, we have developed an MOR-type titanosilicate (denoted as 6M-Ti-M360) with an extremely low framework Ti content (Si/Ti = 300), exhibiting not only ultrahigh catalyst weight-based conversion (81%) but also a record-breaking turnover number (TON = 5845) per Ti site in batchwise ammoximation of cyclohexanone. Its highly isolated and active Ti species took the specific position of defective T3 sites within the eight-member ring side pockets of the MOR topology, evidenced by molecular dimension-dependent shape-selective experiments and theoretical evaluation of the catalytic activation ability of the different crystallographic Ti sites at the molecular level. Despite an extremely low Ti content but with the most active Ti on the defective T3 sites, the 6M-Ti-M360 catalyst maintained the cyclohexanone conversion and cyclohexanone oxime selectivity both as high as 99% for a long lifetime (314 h) in a continuous slurry bed reactor, capable of producing 1100 kg of oxime per gram of Ti. The clarification of the location and local microenvironment of Ti active sites may provide new insights into the exploration and construction of highly active sites in zeolitic catalysts.

Herein, a visible-light-induced umpolung strategy for reductive carboxylation of imines for synthesis of unnatural α-amino acids was disclosed. A reaction mechanism involving electron-donor–acceptor (EDA) complex formation between substrate and oxalate to furnish the desired products was proposed. Oxalic salt in situ generates CO₂ radical anion (CO₂^•–) and carbon dioxide (CO₂) as the key single-electron reductant and carbonyl (C1) source, respectively, during the transformation with or without photocatalyst.

The electrochemical oxidation of alcohols is being explored as a favorable substitute for the oxygen evolution reaction owing to its capability to generate high-value products and lower overpotentials. Herein, we present a systematic investigation into the electrochemical oxidation of 5-hydroxymethylfurfural (HMF), a model biomass platform chemical, on a thin-film nickel catalyst, aiming to investigate the underlying reaction mechanism and shed light on the role of the catalyst’s microenvironment and phase on activity and product selectivity. Utilizing a combined experimental and computational approach, we demonstrate that NiOOH is the active phase for HMF oxidation. Additionally, we find a substantial impact of the electrochemical environment, particularly the electrolyte pH, on the reaction. Under highly alkaline conditions (pH = 13), higher activity for HMF oxidation is observed, accompanied by an increased selectivity toward 2,5-furandicarboxylic acid (FDCA) production. Conversely, a less alkaline environment (pH = 11) results in diminished HMF oxidation activity and a higher preference for the partial oxidation product 2,5-diformylfuran (DFF). Mechanistic insights from DFT studies reveal that geminal diols that are present under highly alkaline conditions undergo hydride transfer via HMFCA, while a shift to an alkoxide route occurs at a lower pH, favoring the DFF pathway. Hydride transfer energetics are also strongly affected by the surface Ni oxidation state. This integrated approach, bridging experimental and computational insights, provides a general framework for investigating the electrochemical oxidation of aldehydes and alcohols, thereby advancing rational design strategies in electrocatalysts for alcohol electro-oxidation reactions.

Replacing H₂ with H₂O as the hydrogen source for the water-involved selective hydrogenation of cinnamaldehyde to cinnamyl alcohol (WSHCC) is very attractive yet is underdeveloped by a much lower H₂O conversion rate than H₂. Here, we report the realization of a high-efficiency WSHCC process by a synergy of CO adsorption and H₂O dissociation over a Au/α-MoC_1–x boundary. It shows a specific molar rate of 60.86 mol mol_Au^–1 h^–1 to cinnamyl alcohol at 96 °C, which is nearly 12-fold that reported earlier, and maintains a high conversion of over 99% and a high selectivity of 77%. Mechanistic studies indicate that the Au/α-MoC_1–x boundary accommodates atomically dispersed Au^δ+ sites for adsorbing CO, vacating oxygen-covered α-MoC_1–x and thereby creating isolated Mo sites for the preferred adsorption and hydrogenation of C═O bonds over that of C═C bonds. This provides a catalyst design strategy for high-efficiency C═O hydrogenation by water.

Molybdenum sulfides (MoS_x) in both crystalline and amorphous forms are promising earth-abundant electrocatalysts for hydrogen evolution reaction (HER) in acid. Plasma-enhanced atomic layer deposition was used to prepare thin films of both amorphous MoS_x with adjustable S/Mo ratio (2.8–4.7) and crystalline MoS₂ with tailored crystallinity, morphology, and electrical properties. All the amorphous MoS_x films transform into highly HER-active amorphous MoS₂ (overpotential 210–250 mV at 10 mA/cm² in 0.5 M H₂SO₄) after electrochemical activation at approximately −0.3 V vs reversible hydrogen electrode. However, the initial film stoichiometry affects the structure and consequently the HER activity and stability. The material changes occurring during activation are studied using ex situ and quasi in situ X-ray photoelectron spectroscopy. Possible structures of as-deposited and activated catalysts are proposed. In contrast to amorphous MoS_x, no changes in the structure of crystalline MoS₂ catalysts are observed. The overpotentials of the crystalline films range from 300 to 520 mV at 10 mA/cm², being the lowest for the most defective catalysts. This work provides a practical method for deposition of tailored MoS_x HER electrocatalysts as well as new insights into their activity and structure.

The Z-scheme system, integrating an oxygen evolution photocatalyst (OEP) with a hydrogen evolution photocatalyst (HEP), is an ideal strategy for photocatalytic overall water splitting (OWS), in which the development of an efficient OEP remains a challenge. Herein, the GaN:ZnO photocatalyst was synthesized by an ammonium halide-based process to perform a recorded apparent quantum yield of 30% at 420 nm for oxygen evolution from water. It made the GaN:ZnO a remarkable OEP for the construction of three distinct Z-scheme OWS systems, including an unbiased-photoelectrochemical sheet, direct collision, and redox-ion-mediated electron shuttle. The features and parameters of each Z-scheme system were discussed in relation to water splitting, and the most efficient one was established by employing [Fe(CN)₆]^3–/[Fe(CN)₆]^4– as an electron shuttle and SrTiO₃:Rh as an HEP. This work not only provides a methodology for synthesizing an efficient GaN:ZnO photocatalyst but also highlights its great potential as an OEP applicable to constructing various Z-scheme OWS systems.

The complex reaction network of catalytic biomass conversions often involves hundreds of surface intermediates and thousands of reaction steps, greatly hindering the rational design of metal catalysts for these conversions. Here, we present a framework of machine learning (ML)-accelerated first-principles studies for the hydrodeoxygenation (HDO) of propanoic acid over transition metal surfaces. The microkinetic model (MKM) is initially parametrized by ML-predicted energies and iteratively improved by identifying the rate-determining species and steps (RDS), computing their energies by density functional theory (DFT), and reparameterizing the MKM until all the RDS are computed by DFT. The Gaussian process (GP) model performs significantly better than the linear ridge regression model for predicting both the adsorption free energies and transition state free energies. Parameterized with energies from the GP model, only 5–20% of the full reaction network has to be computed by DFT for the MKM to possess DFT-level accuracy for the TOF and dominant reaction pathway. While the linear ridge regression model performs worse than the GP model, its performance is greatly improved when only transition states are predicted by the regression model and adsorption energies are computed by DFT. Overall, we find that a high accuracy in adsorption free energies is more important for a reliable MKM than a high accuracy in TS free energies. Finally, based on the GP model with G_OH and G_CHCHCO as catalyst descriptors, we build two-dimensional volcano plots in activity and selectivity that can help design promising alloy catalysts for HDO reactions of organic acids.

Controlling the precise placement of active metals on supports is highly desirable yet challenging, which governs both the reaction pathway and the ultimate outcomes of catalytic reactions. Herein, the Cu species are positioned to the Lewis acidic sites created by the ultrahigh-temperature calcination of TiO₂, where the atomic structures of the Lewis acids are identified as five-coordinated Ti⁴⁺ cations bound to three-coordinated O^2– anions (L_β sites) by in situ characterizations. Owing to the robust chemical affinity, CuO_x manifests itself as a nanopatch. The Cu/TiO₂ catalyst without any modifications exhibits a propylene oxide (PO) formation rate of 44 mmol g_Cu^–1 h^–1 for direct epoxidation of propylene using molecular oxygen (DEP). The PO yield on Cu/TiO₂ can be efficiently correlated with the quantity of the decreased Lewis acids, which demonstrates that the intimated interaction between the Cu species and Lewis acids should be responsible for PO production. Furthermore, density functional theory calculations suggest that Cu⁺ in the Ti–O–Cu interface formed at the L_β sites is the active site of the DEP reaction, with the aid of the adjacent Cu atom. This study provides a Cu-based catalyst for the DEP reaction.

We have achieved the arenophile-mediated, copper-catalyzed dearomative trans-1,2-carboamination of nonactivated arenes with alkyl organometallic nucleophiles. This simple and practical procedure was used to prepare diverse, stereochemically rich alkylated cyclohexadienes from readily available arenes. Synthetic utility was demonstrated through the rapid preparation of complex small molecules difficult to access by conventional routes. Finally, we conducted DFT studies to explore the catalytic process, including a study of the reaction pathway and an examination of the divergent regioselectivity observed with substituted arenes.

Selectivity control of supported metal catalysts, which are most widely utilized in the field of heterogeneous catalysis, is of great scientific significance to obtaining the desired chemical product in a multipath reaction but has remained a grand challenging issue. In this work, we demonstrate that the selectivity of CO₂ hydrogenation from CH₄ to CO can be tuned by a robust and unique support doping strategy by changing the reduction activity of H species over M/Ce_1–xPr_xO_2−δ (M = Ru, Rh) in which metal (M) nanoclusters showed the same existence form on differently doped ceria nanorod supports. The CH₄ selectivity of the catalyst decreased with an increase in the Pr content in the support. The selectivity of CH₄ on Ru/CeO₂ was higher than 90%, while on Ru/Ce_0.2Pr_0.8O_2−δ, the selectivity of CO reached 80%. A variety of techniques, including steady-state isotope transient kinetic analysis (SSITKA) type in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)–mass spectrum (MS), temperature-programmed desorption (TPD) and temperature-programmed surface reaction (TPSR), had been applied in this work to analyze the structure–activity relationship between the doping of Pr and the selectivity of the CO₂ hydrogenation reaction. Ru sites were not directly involved in the hydrogenation of carbon-containing intermediate species (including bicarbonate and formate) during the CO₂ hydrogenation reaction. The active H species on the support sites, which are incorporated in RE³⁺–OH, directly contacted and reacted with the carbon-containing intermediate species. The introduction of Pr in the support weakened the reducing ability of the support, thus decreasing the reducing ability of H species on the surface of the catalyst, which further hindered the conversion of formate into CH₄, resulting in the declined CH₄ selectivity. Our study clearly revealed the important role of support in the CO₂ hydrogenation reaction and proposed a strategy to modulate the reaction selectivity via support doping. By changing the redox performance of the support, the activity of H species on the support can be adjusted. Thus, the conversion of important reaction intermediates (such as formate) can be affected, so as to achieve precise regulation of the reaction products. We have provided a broader perspective for the selective catalyst design of heterogeneous catalysis and the reaction mechanism study of supported metal catalysts.