Applied Catalysis A: General最新文献

Solvent-free and liquid-phase selective oxidation of aromatic alcohols using O₂ as an oxidant is a green strategy for the synthesis of aromatic aldehydes and other carbonyl compounds. Wherein, the design and preparation of heterogeneous catalysts with high activity and selectivity is a hot topic in this process. Herein, a series of manganese oxide-silica (MnSiO_x) composites were synthesized using cetyltrimethylammonium bromide as a soft template. During the preparation process, the amounts of tetraethyl orthosilicate and ammonia and the calcination temperature significantly affected the textural properties and Mn cation distributions of MnSiO_x. The MnSiO_x composites were then employed as catalysts for Pd nanoparticles. In the solvent-free and atmospheric conditions, Pd/MnSiO_x materials showed high catalytic conversions of benzyl alcohol (BZA), and the catalytic activity thereof is related to the fractions of Pd⁰ and Mn³⁺. As the reaction time and temperature are 4 h and 90 °C, the conversion of BZA (feeding dosage: 4 mL) and the selectivity of benzaldehyde are 64.8 % and 94.9 %, respectively. The catalyst can be reused at least five times without any significant loss of activity. Furthermore, the correlation between physiochemical properties and catalytic activity of Pd/MnSiO_x was analyzed.

Traditional catalyst design includes trial-and-error and orthogonal methods. However, these processes usually require large number of experiments to get an optimized formula. Machine learning was applied in designing effective catalyst for selective catalytic reduction (SCR) of nitrogen oxide (NOx). Catalyst formulas and their activities in previous reports were collected and fitted by extreme gradient boosting algorithm and explanatory algorithm-SHapley Additive exPlanations. Mn-Cr coupling was predicted to be the most effective for SCR among various couplings, which was then proved by experimental results. SCR activity of Mn catalyst was increased from 50.3 % to 85.0 % at 150°C after the catalyst was loaded by Cr. Furthermore, machine learning and experimental characterizations revealed that the big total electronegativity of Cr resulted in bidentate nitrate bonding one cation with two oxygens, which was the most active NOx-derived intermediate during SCR. This work is in favor of catalyst design and catalytic-species recognition at the same time.

Electrochemical carbon dioxide reduction (CO₂RR) is a promising approach to accomplish the CO₂ net emission. Ni-based single-atom catalysts (Ni-SACs) with the Ni-N-C structure have been the hotspot in this field. However, its catalytic activity is still unsatisfied. Regulation of the coordination environment of the active site via heteroatom doping is an efficient strategy to improve its catalytic characteristics and activity. Herein, the heteroatom phosphorus is introduced into the N-doped carbon supporter to form Ni-SA/CN-P catalyst achieving the CO Faraday efficiency of 91.8 % at a potential of -1.1 V along with the CO current density 91.2 mA cm^-2 in the flow cell, which is superior to the sample Ni-SA/CN without P dopant. It is attributed that the more defects are built in the Ni-SA/CN-P catalyst due to the different atomic radiuses of P and N atoms. Moreover, the gap between d-band center and Femi energy level is narrowed due to the doped P atoms, which reduces the rate-limiting barrier height leading to the promoted catalytic performance. The cooperation of various items finally results in the overall performance. This work provides a simple method for establishing single-atom catalysts with P doping to improve catalytic performance for CO₂RR.

Thin films, 0.5- and 1.0-nm thick, of CuMn₂O₄ were synthesized on γ-Al₂O₃ using Atomic Layer Deposition (ALD); and their catalytic activities for CO oxidation were measured and compared to that of bulk CuMn₂O₄. For bulk CuMn₂O₄, the surface area decreased dramatically when the sample was calcined at 1073 K; but the area-specific rates for CO oxidation were the same for bulk samples calcined at 473 K and 1073 K. For thin films of CuMn₂O₄ on γ-Al₂O₃, both the surface area and spinel structure were maintained following oxidation at 1073 K or reduction at 973 K. Area-specific, CO-oxidation rates on the ALD-prepared catalysts were somewhat lower than those found on bulk CuMn₂O₄; however, adding an additional ALD cycle of Cu on the CuMn₂O₄/γ-Al₂O₃ increased the rates to the same level as that of the bulk CuMn₂O₄.

Elucidating the structure-performance relationship of catalysts for low-carbon alcohols synthesis from syngas is crucial for designing efficient catalysts. In this study, CuO particle size, reducibility, and the number of oxygen vacancies could be adjusted by changing intercalated Cu complex anions, thereby affecting the catalyst's performance. The characterization results indicated that the insertion of [Cu(C₂O₄)₂]^2- between ZnAl layered double hydroxide resulted in the largest CuO particles (26.5 nm), leading to an increase in the metallic copper surface area. Consequently, the highest CO conversion (13.0 %) was achieved without altering alcohol distribution. On the other hand, when [Cu(EDTA)]^2- was inserted, the catalyst possessed the smallest CuO particle size (8.9 nm), more abundant oxygen vacancies, and enhanced interaction between Cu species and ZnO, which promoted carbon chain growth and resulted in a high C₂₊OH proportion of 75.8 %. Our study thus provides a new perspective on catalyst structures for the syngas production of low-carbon alcohols.

A self-pillared nanosheet ZSM-5 zeolite (SP) loading Zr catalyst is prepared for conversion of levulinic acid (LA) to produce γ-valerolactone (GVL). The hierarchical pore by nanosheet aggregates promotes Zr dispersion with establishment of strong interaction between Zr and zeolite. Moreover, Na ions are introduced to modify the chemical environment of Zr on nanosheet zeolite (Zr/NaSP). In catalytic transfer hydrogenation of LA using isopropanol as H-donor, uniformly dispersed Zr species on SP zeolite is conducive for both conversion of LA as well as production of GVL, in comparison with samples using conventional microporous ZSM-5 as supports (Zr/CZ). More importantly, different from protonated zeolite sample (Zr/HSP), the introduction of alkali sites could attract protons in hydroxyl groups of isopropanol, which accelerates the generation rates of GVL. The as-designed Zr/NaSP catalyst delivers GVL generation rates of 31.9 mmol·g^-1·h^-1, which provides a potential catalyst for GVL production.

Engineering the surface Pt coordination environment is a promising strategy for promoting the kinetically sluggish oxygen reduction reaction (ORR) on Pt-based catalysts. In this study, we achieve the compressive strain effect and electronic effect by Cu and N co-doping to synthesize the PtCuN hollow nanospheres with PtN overlayers (PtCuN@PtN HNSs) using a facile solvothermal synthesis. Electrochemical investigations show that the constructed disordered Pt–N coordination structures effectively facilitate the ORR and stabilize Pt atoms in the compressed lattice, whereas an excessive N-doping can lead to the formation of a structurally unstable Pt nitride phase. Theoretical analyses confirm that the oxygen reduction kinetics on the compressed PtN overlayers are regulated by a synergistic effect resulting from N-doping and lattice compression, circumventing the traditional linear scaling relationships (LSR). The optimized PtCuN@PtN HNSs, with the composition of PtCu_0.29N_1.1, demonstrate an area-specific activity of 1.98 mA cm^–2 and a mass-specific activity of 1.81 A mg_Pt^–1.

A kinetic model was derived for the methanol oxidative dehydrogenation to formaldehyde, methyl formate and dimethoxymethane on sub-monolayer and multilayer V₂O₅/TiO₂ catalysts. Considering a hemiacetal intermediate, the model combines Langmuir-Hinshelwood/Eley-Rideal/Mars-van Krevelen mechanisms, accounting for lattice oxygen redox sites and Brønsted acid sites. The fitted model depends on 4 thermodynamically consistent parameters, adequately simulating yield trends with temperature, residence time, and partial pressure of methanol, oxygen and added water. Oxidation steps follow a Mars-van Krevelen redox cycle, while the dimethoxymethane formation is reversible, as the water addition favored the hemiacetal intermediate. The catalyst with higher vanadia surface density was intrinsically more active (lower activation energy of the rate limiting step), attributed to its higher reducibility, while showing weaker methanol adsorption (lower enthalpy of chemisorption). The increase in reducibility correlates with the transition from monomers to polymers to crystalline vanadia when vanadium content increases, as observed by XRD, Raman spectroscopy and DRS-UV–vis.

Geometrically unsaturated binuclear double-stranded metallohelicates constructed with pyridyl hydrazine ligands and lanthanide metal ions via metal-templated self-assembly. The single-crystal X-ray analysis suggests the formation of helical assembly through its coordination with pyridyl, azomethine nitrogen’s and ketonic oxygen with metal ions. Lanthanide ions are known to possess multiple coordination sites, other labile sites are occupied with solvents and anions. The lanthanide helicates are exhaustively characterized and adopted as a catalyst to synthesize benzothiazole scaffolds starting from 2-fluoroaniline and phenyl isothiocyanate substrates via tandem thiourea intermediate/cyclization pathway. The mechanistic investigation suggests the reaction proceeds via the nucleophilic aromatic substitution pathway. The protocols are extended for the synthesis of drug molecules such as Riluzole and Dimazole.