Kinetics and Catalysis最新文献

This work systematically investigated the influence of fabrication parameters on photoelectrodes of a biphasic indium oxide polymorph (In₂O₃) with cubic (c-) and rhombohedral (rh-) phase contents of 72 and 28%, respectively, deposited on the surface of conductive fluorine-doped tin oxide (FTO) glass. The study examined the effects of varying the concentration of c/rh-In₂O₃ suspension, the composition of the dispersion medium, the number of cycles, and the mode of suspension application onto FTO glass. Linear voltammetry, chronoamperometry, and impedance spectroscopy in the illumination mode were used to demonstrate that the photoelectrode made with a suspension based on isopropyl alcohol at an c/rh-In₂O₃ concentration of 100 g/L exhibited the highest photocurrent density and the lowest charge transfer resistance in an aqueous electrolyte solution of 0.5 M Na₂SO₄ + 0.25 M Na₂SO₃. It has been shown that the optimal approach was to apply three layers using a multistage application mode. The results obtained can be used as a basis for the development of optimization protocols for the photoelectrodes based on oxide-containing systems and photoelectrochemical devices based on c/rh-In₂O₃ material.

Vanadium-containing heteropoly compounds (HPCs), both in homogeneous and heterogeneous forms, represent a very promising class of materials with adjustable acid and oxidative properties. Herein, a catalytically active HPCs of H_3+xPMo_12–xV_xO₄₀ (x = 1–4) gross-composition were prepared by an environmentally friendly H₂O₂-affected approach and heterogenized in the form of insoluble salts with Cs⁺ counterion to obtain stable oxidation catalysts. Structural and textural characteristics of prepared compounds with Cs_2.5+xH_0.5PMo_12–xV_xO₄₀ (x = 1–4) gross-composition were investigated by XRD, TGA, IR-ATR, ICP-AES, and N₂ adsorption-desorption techniques, and their catalytic properties were tested in the oxidation of 5-hydroxymethylfurfural (5-HMF), a valuable biomass-derived platform chemical. The obtained materials were established to demonstrate retention of the initial Keggin structure during precipitation, low solubility in water, and high structural stability upon fourfold treatment with H₂O for 3 h, as well as thermal stability up to 400°C. It was shown that a simple method of replacing H⁺ ions with large Cs⁺ cations allows a traditional homogeneous catalyst to function heterogeneously, which simplifies the process of its separation and recycling. The catalytic performance was shown to decrease gradually with reducing x value. The attained Cs_5.5H_0.5PMo₉V₃O₄₀ and Cs_6.5H_0.5PMo₈V₄O₄₀ solids revealed high activity in 5-HMF transformation to 2,5-diformylfuran with a yield of up to 93%, which opens up prospects for their application in various important fields of synthetic chemistry as heterogeneous oxidation catalysts.

Currently, the search for new effective materials with photocatalytic properties to combat various organic pollutants, including wastewater treatment, is quite urgent. In this work, we obtained a new material based on hexagonal boron nitride modified with hydroxo groups (nanoBN–OH) and the photoactive octahedral cluster complex [{Mo₆I₈}(DMSO)₆](NO₃)₄. Analysis of the obtained samples by transmission electron microscopy showed that the cluster complex in the hybrid material was present in the form of nanoparticles with a diameter of 10–30 nm. Their photocatalytic activity in the decomposition of model dyes, methyl orange and Rhodamine B, was studied, their efficiency was demonstrated, and the effective reaction rate constants were determined.

It has been established that the maximum synergistic effect (more than 100%) is characteristic of the binary mixtures of pentadigalloyl glucose mixed with protocatechuic and vanillic acids in a ratio of 90 : 10 vol % in the reaction with the 2,2'-diphenyl-1-picrylhydrazyl radical in benzene. With an increase in the polarity of the solvent (dimethyl sulfoxide), an increase in the maximum synergistic effect by 15–20% on the average is observed. Using the methods of quantum chemical calculations and difference UV spectroscopy, it is shown that the resulting effect of the compositions of pentadigalloyl glucose with monomeric phenols depends on the following two mechanisms of synergistic action: the first mechanism is related to the formation of the intermolecular H-complex between reagents, which exhibits higher antiradical activity than that of the initial compounds; the second one is associated with the reduction of oxidized forms of the weaker antioxidant (monomeric phenol) by the stronger antioxidant (pentadigalloyl glucose). The mixture of pentadigalloyl glucose with methoxylated forms of plant phenols is a promising synergistic composition with high antiradical activity.

In this study, hydrolysis precipitation was employed to quickly and efficiently synthesize Cu²⁺ doped BiOCl nanosheets. The doping of Cu²⁺promoted the generation of oxygen vacancies on the surface of BiOCl and the separation of photogenerated electron hole pairs. Oxygen vacancies, as electron donor centers and reactive sites, can effectively enhance the catalytic performance of BiOCl. According to performance testing, the nitrogen fixation ability of 3 wt % Cu/BiOCl (259 μmol L^–1 h^–1) is 1.7 times that of BiOCl (156 μmol L^–1 h^–1). This synthesis technique provides a novel approach for the inexpensive, effective, and high-yield production of photocatalysts.

A highly efficient protocol was developed for the synthesis of fructone spice from the ketalization of ethyl acetoacetate with ethylene glycol utilizing the sulfonated polydivinylbenzene (PDVB-SO₃H) solid acid catalyst. A comparative analysis revealed that PDVB-SO₃H exhibited better catalytic activity and reusability than conventional H₂SO₄ and p-toluene sulfonic acid. The impact of reaction conditions, including temperature, reaction time, catalyst dosage, and molar ratio of reactants, was extensively investigated in order to optimize the reaction parameters. The results revealed the remarkable catalytic efficiency of PDVB-SO₃H in synthesizing apple ester flavor, achieving a conversion rate exceeding 99% under reflux conditions with a ketone to alcohol ratio of 1.5. Furthermore, PDVB-SO₃H solid acid demonstrated its versatility by enhancing the synthesis of a variety of fruit ketone flavors with high conversion rates. Notably, the catalyst displayed excellent recyclability, remaining active for up to six cycles without any noticeable decline in performance. Therefore, PDVB-SO₃H solid acid exhibits immense potential for utilization in the chemical industry.

This review provides a comprehensive survey of the preparation and application of homogeneous and heterogeneous boron and indium alkoxide catalysts and typical Meerwein–Ponndorf–Verley (MPV) reduction process techniques that are usually employed in the production of alcohol. A significant number of preparation and application methods are now available for various heterogeneous catalysts synthesized with some mesoporous silica nanoparticles. In this review article, preparation, characterization, application and advantages of boron and indium alkoxides grafted metal-free mesoporous heterogeneous catalysts are discussed. Also, recent research on applying mesoporous MCM-41 and SBA-15 to heterogeneous catalysis in synthesizing heterogeneous MPV catalysts has been reviewed. The potential heterogeneous catalysts that could be derived from the grafting of alkoxides on mesoporous materials, methods of preparing solid boron and indium alkoxide catalysts, as well as reusability and leaching analysis are discussed in detail. We think that the development of new, environmentally friendly, efficient, and selective catalytic procedures for carbonyl reduction and alcohol formation, represents a fundamental research aim in synthetic chemistry. In this context, this review can make an important contribution to organic synthesis.

The polymer semiconductor material known as graphitic carbon nitride (g-C₃N₄) has been extensively utilized for the removal of pollutants in wastewater treatment due to its notable visible photocatalytic efficiency, cost-effectiveness, straightforward synthesis, and chemical robustness. Nonetheless, unmodified g-C₃N₄ still exhibits deficiencies including suboptimal visible light absorption, pronounced electron-hole recombination, and wide band gaps, resulting in constrained photocatalytic efficacy. Through extensive research efforts, diverse modification approaches have been devised to enhance its photocatalytic capabilities. This paper systematically introduces the development history, preparation methods, photocatalytic mechanisms, advantages, and disadvantages of novel g-C₃N₄ materials, the various modification strategies including morphology control, element doping, defect construction, semiconductor coupling, and hetero-structure construction. In this paper, the preparation process, characterization results, practical applications, and performance enhancement effects of various elementally doped g-C₃N₄ materials in pollutant removal are discussed in detail, indicating the advantages of multielement doping modification strategy have obvious advantages in improving the photocatalytic performance of g-C₃N₄, highlighting the future prospects of g-C₃N₄ materials.

The Co/BEA zeolite catalyst was found to exhibit exceptionally high activity in ozone catalytic oxidation (OZCO) of methane impurities in air, and it provided CH₄ conversion >85% in the temperature range 90–170°С at a high gas hourly space velocity (100 000 h^–1). A comparative study of the catalytic performance of 0.5% Co/BEA, 5% Co/BEA, and 5% Co/SiO₂ samples was performed for elucidating the nature of the active sites on which the process takes place. The comparison of the catalytic data with the results of catalyst characterization by electron microscopy, UV spectroscopy, X-ray diffraction analysis, and temperature-programmed reduction allowed us to conclude that the active sites of low-temperature methane oxidation are Co²⁺ ions located in the cationic positions of the zeolite framework, and the 0.5% Co/BEA catalyst had the highest activity in methane oxidation.

Understanding the kinetics and mechanism of formation of charged species in flames is of great importance for the development of ion-sensitive combustion control technologies. The development of predictive models involving ion-molecular reactions, however, is hampered by the lack of experimental data. The paper presents the results of our study of the spatial distribution of cations naturally occurring in a fuel-rich, non-sooting, laminar premixed ethylene/oxygen/argon flame using flame sampling molecular beam mass spectrometry. Particular attention is paid to the interpretation of the obtained mass spectra of cations, which are distorted by the influence of the sampling probe. The reliability of the proposed interpretation of the spectra is confirmed by consistency between the cationic and neutral flame structures. The study focused on cations with the general formula C_xH(_{y}^{ + }) (53 < m/z < 165), actively formed in the reaction zone of the fuel-rich flame. Two main mechanisms of their formation are discussed: proton transfer from HCO⁺ and H₃O⁺ (key cations of flame) to neutral intermediates whose mass is 1 amu smaller and gradual increase in the mass of ions in the reactions of lighter C_xH(_{y}^{ + }) ions with neutral intermediates having high concentrations in the flame (acetylene, diacetylene, propylene, propyne, etc.).