Applied Catalysis A: General最新文献

Low-temperature selective catalytic reduction of NO_x with ammonia (NH₃-SCR) over zeolite catalysts remains a great challenge in diesel exhaust purification. Herein, Cu-LTA zeolite with excellent hydrothermal stability was composited with a small proportion of SmMnO_x oxides, the composite catalytic system efficiently resolves the low-temperature activity challenge encountered by Cu-LTA. The promoting pathways revealed the presence of active nitrite intermediates formed on SmMnO_x by activating NO, that were able to migrate to the Cu-LTA and can be further decomposed on the Brønsted acid sites. Compared to the continuous deposition of nitrates in Cu-LTA, the presence of SmMnO_x in composite catalysts efficiently reduced the accumulation of inert nitrate and improved the nitrate deposition phenomena. This innovative research would provide a rational strategy to break the barrier of limited low-temperature performance faced by zeolite catalysts, effectively promoting the NO_x removal in vehicles sources.

Developing a highly efficient Ni-based hydrodeoxygenation catalyst is crucial for the production of renewable biodiesel. Herein, a mesoporous TS-1 zeolite supported Ni catalyst (Ni/TS-1-M) exhibited exceptional hydrodeoxygenation (HDO) activity and achieved 100 % yield of deoxygenated hydrocarbons (97.3 % pentadecane vs 2.7 % hexadecane), outperforming other catalysts such as Ni on mesoporous ZSM-5 (Ni/ZSM-5-M), mesoporous Silicalite-1 (Ni/Silicalite-1-M) and TiO₂ (Ni/TiO₂). The Ti(IV) atoms in the form of TiO₄ and TiO₆ can transfer its electron to nearby metal Ni, leading to the increase in electron density of metal Ni, which enhanced the hydrogenation activity and facilitated the C–C bond cleavage of the hexadecanal to produce pentadecane. Furthermore, the framework Ti(IV) species accelerated the esterification process to generate palmityl palmitate, which was easily hydrogenolyzed to the main intermediate of hexadecanol under the synergistic effect of metal Ni and Ti(IV) on Ni/TS-1-M catalyst. The formed hexadecanol mainly underwent successive dehydrogenation/decarbonylation process to transform into pentadecane.

Interzeolite conversion is a convenient and low-cost method to get Cu-SSZ-13 zeolite for ammonia selective catalytic reduction (NH₃-SCR) of NO, but it is usually difficult to regulate the Si/Al ratio of the SSZ-13 in a wide range by interzeolite conversion. In this work, Cu-SSZ-13 catalysts with Si/Al ratios of 5, 10 and 20 were accurately synthesized by zeolite Y conversion with additional Si source. Specifically, the physical properties of Cu-SSZ-13 were characterized by XRD, SEM, ICP-AES and BET. The Al distribution and Cu²⁺ locations in Cu-SSZ-13 were investigated by ²⁹Si and ²⁷Al MAS NMR, DR UV–vis, H₂-TPR and EPR. The results show that Cu-SSZ-13 with Si/Al ratio of 10 shows the considerable NH₃-SCR activity and hydrothermal stability simultaneously. Moreover, different types of relationships between the reaction rate constant k and the content of α-Cu²⁺, β-Cu²⁺ species were found, indicating the diverse catalytic properties of the two active copper sites.

Herein, a novel Z-scheme Co-MOF/Bi₂MoO₆ was synthesized by in-situ growth method. The photocatalytic CO₂ reduction effect of Co-MOF/Bi₂MoO₆ was significantly improved, and the formation rates of CO and CH₄ reached 19.76 and 8.24 μmol·g⁻¹·h⁻¹, which corresponded to 1.61 and 2.38 times of Co-MOF (CO: 12.31 μmol·g⁻¹·h⁻¹) and Bi₂MoO₆ (CH₄: 3.46 μmol·g⁻¹·h⁻¹), respectively. The increased photocatalytic activity of Co-MOF/Bi₂MoO₆ resulted from the enhanced visible light capture capability and the Z-scheme heterojunction formed among Co-MOF and Bi₂MoO₆, which promoted the efficient separation of photogenerated carriers while retaining the highest redox capacity. The Z-scheme charge transfer direction of Co-MOF/Bi₂MoO₆ was confirmed by DRS, XPS, ESR, UPS, and the photocatalytic reaction mechanism was explained. In addition, the active substances and intermediates of Co-MOF/Bi₂MoO₆ in the photocatalytic CO₂ reduction process were investigated using ESR and in-situ FT-IR. The work offers a idea for building MOFs-based heterojunctions to improve the effect of photocatalytic CO₂ reduction.

Electrocatalytic CO₂RR is an ideal method. It is capable of converting CO₂ into usable fuels and valuable chemical products. Electrocatalytic CO₂RR produces a wide range of chemicals. Of these, ethanol (EtOH) is favored for its wide industrial and commercial value. However, electrocatalytic CO₂RR preparation of EtOH involves C-C coupling reactions and is a multi-electron transfer process. For this reason, the efficient electrochemical conversion of EtOH by CO₂RR remains a great challenge. The preparation of EtOH by electrocatalytic CO₂RR involves the interference of a competing hydrogen evolution reaction as well as some other reaction intermediates. This limits the improvement of Faraday efficiency of ethanol (FE_EtOH) and the current density of ethanol (J_EtOH). To improve ethanol selectivity, the researchers designed and modified the catalysts using engineering regulation effects such as reaction conditions engineering regulation, surface engineering regulation, interfacial engineering regulation, and single atom engineering regulation, and achieved excellent results. Therefore, it is important to understand the key factors affecting the catalyst activity by different engineering regulations and to apply a combination of engineering regulations to the catalyst development. Therefore, this paper firstly provides a comprehensive summary of the catalysts applied for the preparation of EtOH by electrocatalytic CO₂RR, including two major categories of catalysts containing pure metal active components and catalysts without pure metal active components. Subsequently, the main effects of engineering modulation on catalyst activity are analyzed and summarized in detail, respectively. Finally, the future challenges and development prospects of electrocatalytic CO₂RR for EtOH preparation were highlighted.

Zirconium-based metal organic frameworks (Zr-MOFs) are considered as promising photocatalysts due to their excellent stability, unique pore structure, and versatile photocatalytic applications. To strengthen the visible-light absorption, a well-designed targeted MOFs photocatalyst was fabricated by a solvothermal method with Co-tetrakis (4-carboxyphenyl) porphyrinate (Co-TCPP), 1,3,6,8-tetra(4-carboxyphenyl) pyrene (TBAPy), and Zr clusters as sensitizer, ligands and active sites, respectively. Benefiting from the excellent photo-responsiveness of Co-TCPP, the robust catalytic ability of Zr clusters, the promising electron transfer ability of pyrene moiety, the prepared Zr-Co MOF@TBAPy exhibit excellent photocatalytic performance and stability. A high reduction rate of 127.42 μmol g⁻¹ h⁻¹ from CO₂ to CO, this is 3.5 and 2.8 times that of Zr-TBAPy and Zr-Co MOF, respectively. The photocatalytic performance of CO₂ reduction coupling with selective oxidation of benzyl alcohol (BA) to benzaldehyde (BD) was also tested. The transferring pathway of photogenerated electron from the photosensitive unit to the active site mediated by the electron transport unit was further confirmed by density-functional theory (DFT) calculations, providing intuitive insights into the catalytic mechanism. This work manifests that well-designed MOFs integrated with functional moieties is a feasible strategy for developing high performance MOF based photocatalyst.

In this work, boron doped graphitic carbon nitride materials (BgCN-x) were successfully prepared by thermal copolymerization of melamine and boric acid. The comprehensive characterization using various techniques, including powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), UV-Visible spectroscopy (UV-Vis), Field emission scanning electron microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDS), Field emission transmission electron microscopy (FETEM), and X-ray photoelectron spectroscopy (XPS) revealed the uniform doping of boron in the tri-s-triazine rings of g-C₃N₄ by substituting the carbon or nitrogen atoms. Furthermore, the basic site concentrations of the catalysts were evaluated using CO₂-TPD technique. The BgCN catalysts exhibited significantly enhanced catalytic activity in the base-catalyzed Knoevenagel condensation between salicylaldehyde and diethyl malonate for coumarin synthesis. This work underscores the potential of boron-doped or two-dimensional boron-dominant materials as promising candidates for metal-free heterogeneous base catalysis, paving the way for further advancements in the field.

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.