Catalysis Letters最新文献

Waste cooking oils (WCO) are residues capable of causing severe environmental harm if disposed of incorrectly. Nonetheless, they can be easily reused as lipid feedstock for producing biodiesel through the hydroesterification route, therefore being the chief objective herein. In this route, there is an initial hydrolysis reaction of WCO into free fatty acids (FFA) and glycerol, followed by esterification of FFA into esters (biodiesel) using alcohol and free lipases in both reactions. The hydrolysis step was carried out using lipase from Candida rugosa (CRL) and the central composite rotatable design (CCRD) selecting WCO and enzyme contents as variables, and 100% hydrolysis of WCOs into FFA was observed after 150 min of reaction at 40ºC and 10% content for both variables. In the esterification step, reactions were catalyzed using Eversa® Transform 2.0 (ET 2.0) and the FFA:ethanol molar ratio, enzyme content and reaction time were evaluated, thus achieving maximum conversion of 91.94% of FFA into biodiesel in a FFA:ethanol molar ratio of 1:2 and enzyme content of 5.0% after 4 h of reaction. The produced biodiesel presented high unsaturation content in its composition, which is advantageous since it favors fluidity at low temperatures and assists in avoiding the obstruction of engine injection systems.

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A series of MoVTeNbOx catalysts with different Sr doping amounts were prepared by spray-drying method and used in the one-step oxidation of propane to acrylic acid. The results showed that Sr doping does not cause significant damage to the M1 phase structure, and moderate Sr doping increases the relative content of the M1 phase by inhibiting the transformation to the MoO₂ phase. Concurrently, the introduction of Sr alters the pore size distribution of the catalyst, leading to a trend toward a transition from mesoporous to microporous catalysts. The introduction of Sr reduces the surface acidity of MoVTeNbOx, inhibits the peroxidation of acrylic acid, and improves the distribution of surface elements. Moderate Sr doping promotes an increase in the Te⁴⁺ content on the surface of MoVTeNbOx, which is beneficial for the formation of acrylic acid. Compared with the undoped MoVTeNbOx sample, the sample with the Sr/Mo atomic ratio of 0.015 possessed the highest M1 phase content (97%) and the best catalytic performance, with an increase from 46 to 77% for the selectivity to acrylic acid and an increase from 30 to 49% in for the acrylic acid yield.

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TiO₂ catalytically active coating on TC4 titanium alloy was prepared through plasma electrolytic oxidation (PEO) utilizing aqueous electrolytes. The elemental and phase composition, microstructure, and catalytic performance of the coating was characterized by EDS, XRD, SEM, UV-Vis, TOC, and COD methods, respectively. The coating, with a surface porosity of 20%, primarily consists of rutile-type TiO₂ and amorphous vanadium compounds. The catalysis originates from the synergistic interaction between the porous TiO₂ coating and ozone activation, where the plasma-electrolytic porous architecture enhances surface adsorption and radical-mediated from ozone decomposition reaction pathways. Combined with ozone oxidation, the coating exhibits excellent catalytic performance in degrading methyl orange (MO), and the degradation rate has been increased. Notably, the catalyst showed the most significant effect in catalytic ozonation of a 10 mg/L MO, achieving a degradation rate of up to 95.6% in 60 min, representing 71.8% enhancement compared to ozone oxidation. What’s more, the result of TOC and COD jointly confirms that the PEO catalytic coating exhibits high efficiency for the catalytic degradation of low-concentration MO solution. This study establishes a potential application in advanced oxidation processes for the degradation of organic pollutants.

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The liquid-phase selective oxidation of benzyl alcohol (BZA) by atmospheric oxygen is a more sustainable and cleaner strategy for the synthesis of benzaldehyde (BZL) compared with the traditional hydrolysis of chlorobenzene. Herein, a series of C₃N₄–CeO₂ composites were prepared and then utilized as catalyst supports to load Pd nanoparticles. The effects of the amount of carbon nitride (C₃N₄) and the calcination conditions on the physicochemical properties of C₃N₄–CeO₂ materials were investigated. In the solvent-free selective oxidation of BZA, the Pd/C₃N₄–CeO₂ materials demonstrated higher catalytic activity than Pd/C₃N₄ and Pd/CeO₂. Under the reaction temperature of 90 °C and 4 mL of BZA, the BZA conversion could reach 84.6%, whereas the selectivity of benzaldehyde was 98.7%. In addition, the solid catalyst could be reused six times while the conversion did not significantly decrease. Based on the characterization results, the possible catalytically active sites of 2Pd/C₃N₄–CeO₂-1 for the selective oxidation of BZA were Ce³⁺ and oxygen vacancies, and the introduction of C₃N₄ effectively increased the content of these two species.

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A highly efficient Fe-Sn-Cu ternary oxide catalyst was developed for the Baeyer-Villiger oxidation of cyclohexanone using O₂/benzaldehyde to synthesize ε-caprolactone (ε-CL), a key precursor for biodegradable polycaprolactone. Catalysts with varying Cu ratios were synthesized via co-precipitation and characterized. Moderate Cu doping (n(Fe): n(Sn): n(Cu) = 1:1:0.1) optimized mesoporous structure and mass transfer, with SnO₂ as the skeleton and highly dispersed Fe₂O₃/CuO creating synergistic active sites. BET analysis showed that this specific composition achieved an optimized mesoporous architecture with the largest average pore diameter (37.27 nm), enhancing mass transport and active site accessibility compared to the un-doped (28.55 nm) and over-doped (30.52 nm) variants. XPS analysis confirmed the coexistence of active species Fe³⁺, Sn⁴⁺, and Cu²⁺, where the incorporation of Cu²⁺ is crucial for accelerating the oxidation of benzaldehyde, the rate-determining step. Under optimal conditions (55 °C, 5 h, cyclohexanone/benzaldehyde = 1:3, O₂ flow = 25 mL·min⁻¹), Fe-Sn-0.1Cu achieved 99.9% cyclohexanone conversion, 99.9% ε-CL selectivity, and 98.5% benzaldehyde conversion. The catalyst retained activity over 9 cycles, demonstrating retained activity. Its low-cost preparation and potential for industrial application were highlighted. Notably, phenyl formate, a benzaldehyde oxidation byproduct requiring chromatographic separation, was identified to prevent analytical inaccuracies.

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Catalytic hydrolysis has been recognized as one of the most effective strategies for eliminating carbonyl sulfide (COS) from natural gas, a process that relies on strong adsorption capability and efficient molecular activation. Owing to the outstanding physicochemical properties of titanium dioxide (TiO₂) in COS hydrolysis, bismuth (Bi) ions were incorporated into the TiO₂ framework to induce lattice distortions and defect-rich active centers. Moreover, Bi³⁺ cations are generally regarded as weakly basic, and their interaction with surface O²⁻ anions enhance the overall surface basicity, which contributes to superior COS elimination. In the next step, interlaced CuO nanosheets (NS-CuO) were fabricated using a scalable alcohol-mediated sol–gel approach, which then served as a structural support for the controlled anchoring of Bi-doped TiO₂ nanoparticles (3Bi-TiO₂@NS-CuO) through an isoelectric-point-guided annealing route. The resulting heterojunction was deliberately engineered to accelerate charge carrier generation with excellent dynamics and efficient pathways. Under optimum experimental parameters, the 3Bi-TiO₂@NS-CuO hybrid achieved full COS removal at 60 °C and persevered stable activity for more than 30 h without observable deactivation. The cooperation of Bi-TiO₂ and NS-CuO promoted effective water adsorption, activation, and dissociation, thereby generating abundant surface hydroxyl (–OH) groups, which were decisive for boosting hydrolysis at reduced temperatures. Overall, this work advances the understanding of heterogeneous catalytic systems for the deep elimination of complex organic sulfur pollutants, offering promising routes for practical low-temperature applications.

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Bi-doped TiO2 nanoparticles anchored on CuO nanosheets create defect-rich heterojunctions with enhanced surface basicity, accelerating COS hydrolysis at low temperatures. The 3Bi-TiO2@NS-CuO catalyst achieves complete COS removal with superior stability and selectivity, offering a promising strategy for efficient natural gas purification.

The development and synthesis of ligands with unique capacities to modify and improve the UiO-66-NH₂ framework have always attracted the attention of researchers. In this regard, we succeeded in synthesizing a new ligand, 1,4-phenylene bis(cyanoguanidine), from cyanoguanidine derivatives with crosslinking capacity. Then, to modify and improve the UiO-66-NH₂ framework, the synthesized ligand was used to introduce 1,4-phenylene bis(biguanide) into the framework via polymerization. Incorporation of a bidentate biguanide ligand into the UiO-66-NH₂ scaffold enhances the functionality of the framework by forming stable complexes with Cu(OAc)₂ and minimizing metal ion leakage during the reaction. Characterizations of the functionalized MOF were conducted using various techniques, including FTIR, FE-SEM, EDX, XRD, AAS, TGA, and N₂ adsorption–desorption, followed by catalytic evaluation of the composite. The synergistic effect between copper and zirconium resulted in outstanding performance of the nanocatalyst in synthesizing polyhydroquinoline and tetrahydrobenzo[b]pyran derivatives. The results obtained from the comparison of the synthesized nanocatalyst with UiO-66-NH₂@Cu(II), UiO-66-NH₂-BBG, and pure UiO-66-NH₂ showed that the improved catalytic performance of UiO-66-NH₂-BBG@Cu(II) can be attributed to the integration of the copper complex of the 1,4-phenylene bis(biguanide) ligand into the MOF structure. The modified UiO-66-NH₂ showed higher thermal stability than the parent UiO-66-NH₂. This nanohybrid demonstrated excellent recyclability and maintained its catalytic activity over five consecutive cycles without significant degradation.

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CuZrO₂ catalysts exhibited good performance in catalyzing the conversion of ethanol to 2-pentanone. However, those prepared by the traditional co-precipitation method had a small specific surface area. In this study, we employed an aging treatment at different temperatures to post-modify the CuZrO₂ catalysts. Detailed characterization results showed that the specific surface area of the catalysts increased with rising aging temperature, and the dispersion of Cu species was significantly improved. The highly dispersed Cu species promoted the dehydrogenation of ethanol to acetaldehyde, leading to an abundant formation of acetate species on the catalyst surface, which served as the main intermediates for ketone formation. Additionally, after the high-temperature aging treatment, medium-strong and strong basic sites emerged on the catalyst surface, further enhancing the condensation reaction. When the aging temperature was 80 °C, the catalyst exhibited the highest content of strong basic sites, and the total ketone selectivity reached a maximum of 63.9%, with the selectivity to 2-pentanone being 28.7%. However, excessively high aging temperatures led to the formation of large Cu particles and reduced the Cu–Zr synergistic effect, ultimately resulting in a decrease in ketone selectivity. Moreover, the ketone selectivity over the C/Z-80 catalyst was only 35.6%, indicating that the catalyst preparation method had a significant influence on the product distribution.

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