Kinetics and Catalysis最新文献

The properties of Pd/HZSM-5 and Pd–nP/HZSM-5 catalysts were studied in direct synthesis and side processes of decomposition and hydrogenation of H₂O₂ under mild conditions in ethanol and aqueous ethanol in the presence of an acid inhibitor. It was shown, using HRTEM, XRD, and ICP MS methods, that modification with phosphorus led to the formation of highly dispersed X-ray amorphous systems, which are structurally disordered solid solutions of phosphorus in palladium. The main factors governing the promoting effect of phosphorus on the yield of H₂O₂ are considered. It was established that the use of a zeolite support in the H form, along with the phosphorus and acid modifiers, inhibits the side process of H₂O₂ decomposition.

The purpose of this work was to study the catalytic properties of mono- and bimetallic nanoparticles of the copper–silver system of variable composition supported on aluminum oxide in the conversion reactions of protium modifications and deuterium–hydrogen exchange. From a comparison of the temperature dependences of the specific catalytic activity of samples in the two test reactions, a conclusion on different reaction mechanisms was drawn. It was shown that, compared to the bulk metals, Cu_nAg_m nanoparticles had catalytic properties over a wide temperature range down to –196°C. In the chemical reaction of isotope exchange in molecular hydrogen, a synergistic effect was observed, which indicated the interaction of metals in bimetallic nanoparticles.

The thermodynamic parameters of formation reactions (total energy at 0 K, enthalpy, and Gibbs free energy at a temperature of 298.15 K and a pressure of 101 325 Pa) were estimated in the B3LYP-D3(BJ)/6-311++G** approximation for the products of ionic alkylation of adamantane and lower alkyladamantanes with ethylene and propylene. Aluminum chloride was used as an acid catalyst model. The quantum-chemical calculations demonstrated the effect of methyl groups in adamantanes and the molecular weight of the olefin on the energetics of formation of the corresponding alkyl- and alkenyladamantanes.

The photocatalytic generation of hydrogen from aqueous solutions of formic acid under irradiation with visible light with the use of tantalum-containing metal–ceramic composites based on silicon nitride was investigated depending on the substrate concentration and the pH of suspension in the absence and with the addition of hydrogen peroxide. These compounds were obtained by self-propagating high temperature synthesis (SHS) using the combustion of ferrosilicon aluminum (FSA) and a mixture of silicon and aluminum powders with tantalum additives in an atmosphere of nitrogen. It was found that the dependence of the rate of photocatalytic hydrogen production on the concentration of formic acid without hydrogen peroxide was described by the Langmuir–Hinshelwood mechanism. In the presence of hydrogen peroxide, the rate of the photocatalytic process sharply increased with the concentration of formic acid. The highest rate of hydrogen evolution from formic acid was observed on an iron-containing composite synthesized from FSA without the addition of hydrogen peroxide, and it amounted to 4.55 µmol/min.

In this study, the kinetics of catalytic degradation of methyl red, an anionic azo dye, by hexacyanoferrate(III) ions in the presence of ultrafine Ir–Cu bimetallic nanoparticles has been investigated. The effect of various parameters, including the concentration of dye, oxidant, Ir–Cu bimetallic nanoparticles (BMNPs), and solution pH on the reaction rate was investigated by measuring the light absorption at a wavelength of 425 nm, corresponding to the maximum absorption of the dye. The results reveal that the reaction follows first-order kinetics with respect to the concentration of hexacyanoferrate(III), methyl red, and Ir–Cu BMNPs at an optimum pH of 8.0 and a constant temperature of 40 ± 0.1°C. In order to determine how electrolytes interact with the reaction rate, the impact of ionic strength on the degradation rate was also examined. The high catalytic activity of Ir–Cu BMNPs was demonstrated by a three to four-fold rise in the reaction rate with increasing concentration of Ir–Cu BMNPs (particle size ca. 0.98nm). Thermodynamic parameters including activation energy (E_a), enthalpy of activation (ΔH^#), entropy of activation (ΔS^#), and free energy of formation (ΔF^#) of the reaction were calculated by analyzing the reaction rate at four different temperatures within the 40 to 55°C range. The low value of activation energy also suggests a high degradation rate. A reaction mechanism through complex formation was proposed based on the experimental findings which were supported by the analysis of the products formed. The formation of simpler and less hazardous products (1,5-pentanediol and benzoic acid) was verified by UV–Vis spectroscopy and liquid chromatography and mass spectroscopy (LC–MS). The assessment of turnover frequencies for each catalytic cycle also proved the stability and reusability of the catalyst. As a result, the discovery offers an innovative and highly cost-effective solution for environmental safety against dye contamination, with the potential for expansion to additional toxins.

Gold nanoparticles supported over mesoporous ceria (Au/CeO₂), titania (Au/TiO₂) and iron oxide (Au/Fe₂O₃) were prepared by deposition-precipitation with urea and used for toluene oxidation. The mesoporous CeO₂, Fe₂O₃, andTiO₂ were synthesized employing a hard-template approach using SBA-15 as the template. The catalysts were characterized by BET, X-ray diffraction (XRD), H₂-temperature programmed reduction (H₂-TPR), diffuse reflectance UV-Vis spectroscopy (DR/UV-Vis), and high-resolution transmission electron microscopy (HRTEM). Based on the temperature required to achieve 50% toluene conversion in the oxidation reaction (T_50%), the activity sequence was Au/CeO₂ > Au/Fe₂O₃ > Au/TiO₂. The Au/CeO₂ catalyst was the most active catalyst, achieving 50% toluene conversion at 240°C and full toluene conversion at 295°C demonstrating high stability over successive catalytic runs.

The photocatalytic activity of the g-C₃N₄/TiO₂ composite samples in the processes of dye (methylene blue) decomposition and hydrogen evolution from an aqueous ethanol solution under the action of visible radiation (400 nm) has been studied. A new original method for the synthesis of the g-C₃N₄/TiO₂ composite by depositing g-C₃N₄/TiO₂ to TiO₂ nanoparticles during sol-gel synthesis is proposed. The synthesized photocatalysts were characterized by X-ray diffraction, low-temperature gas adsorption, X-ray photoelectron spectroscopy, high-resolution transmission microscopy, and diffuse reflectance spectroscopy in the UV and visible regions. The maximum activity in the hydrogen evolution reaction was 1.3 mmol ({text{g}}_{{{text{cat}}}}^{{ - 1}}) h^–1, which exceeds the rate of hydrogen evolution on the unmodified g-C₃N₄ and TiO₂ samples.

Iron oxide-modified 1Pd0.5Fe and 1Pd10Fe catalysts with a target content of 1 wt % Pd and 0.5 or 10 wt % Fe have been synthesized by the wet impregnation of Al₂O₃ with iron and palladium nitrates. The catalysts have been compared with each other and with a monometallic 1Pd catalyst in diclofenac (DCF) hydrodechlorination (HDC) in dilute aqueous solutions at 30°C in batch and flow reactors after high-temperature (320°C) and mild reduction (30°C), the latter being run in a batch or flow reactor. X-ray photoelectron spectroscopy (XPS) has revealed that, after reduction at 320°C, the catalysts contain mostly Pd⁰, Fe²⁺, and Fe³⁺. The Fe²⁺/Fe³⁺ ratio on the surface increases with a decrease in the iron content. The reduction of Pd²⁺ to Pd⁰ can occur even at 30°C; however, on the 1Pd0.5Fe surface, it is significantly less effective than that on 1Pd10Fe. According to XPS, temperature-programmed reduction, and diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO, modification with iron oxides leads to an increase in the palladium content on the surface compared with that on 1Pd, contributes to the formation of new Pd–O–Fe sites, and affects the reducibility of palladium. These effects enhance with an increase in the iron content. The iron-modified catalysts reduced at 320°C exhibit similar activity and stability in DCF conversion in flow and batch systems. The 1Pd10Fe catalyst, unlike 1Pd0.5Fe, is highly efficient and stable even after mild reduction at 30°C. Under flow conditions, it provides a DCF conversion comparable to that provided by 1Pd and a selectivity in the DCF HDC reaction that is higher than that provided by 1Pd, which is also active in hydrogenation.

This paper demonstrates that relative reactivity estimated under competition of several similar substrates can be applied to visualize the dynamics of changes in a catalyst under the conditions of a complex catalytic process. The fundamental advantage of the proposed approach is that the state of an active catalyst can be monitored throughout the catalytic reaction without differentiation of the kinetic data on the concentrations of reacted substances.

Changes in the composition of immobilized [M(COD)Cl]₂–NH₂–C₃H₆–SiO₂ and [M(COD)Cl]₂–P(Ph)₂–C₂H₄–SiO₂ (where M = Ir, Rh) catalysts in the gas-phase selective hydrogenation of propylene, propyne, and 1,3-butadiene with parahydrogen (p-H₂) have been studied by the XPS method. It has been proposed that the M/Cl atomic ratio should be used as an indicator of the structural stability of the anchored complex both at the sample synthesis stage and in the reaction. Based on comparison of XPS data and results of catalytic tests using parahydrogen-induced nuclear polarization, it has been shown that the stability of the anchored {[M(COD)Cl]₂–Linker–SiO₂} complex during hydrogen activation is a key factor in the catalytic behavior of the systems. The stability of the complex is affected not only by the chosen metal and linker, but also by the nature of the substrate subjected to hydrogenation.