Kinetics and Catalysis最新文献

In conditions of depletion of mineral reserves, plant biomass is considered a renewable natural resource that can be photocatalytically processed to produce energy-intensive and environmentally friendly hydrogen fuel. In this regard, the present article focuses on the improvement of photocatalytic activity of the layered perovskite-structured niobate HCa₂Nb₃O₁₀ in the reactions of hydrogen production from aqueous solutions of typical plant biomass components, glucose and xylose, via its exfoliation into nanosheets followed by their reassembly and modification with a Pt cocatalyst. The reassembled compound obtained was shown to outperform in the activity the initial niobate and reference photocatalyst TiO₂ P25 Degussa up to 6.3 and 5.3 times, respectively, providing a hydrogen production rate up to 24.2 mmol h⁻¹g⁻¹ and apparent quantum efficiency up to 10% in the mid-near ultraviolet range.

The bond dissociation enthalpy of the N–H bond was calculated for the following compounds: 1-((E)-1,5-diphenylpent-1-en-4-yn-3-ylidene)-2-(o-tolyl)hydrazine, 1-((E)-1-(4-methoxyphenyl)-5-phenylpent-1-en-4-yn-3-ylidene)-2-phenylhydrazine, 1-((E)-1-phenylpent-1-en-4-yn-3-ylidene)-2-(p-tolyl)hydrazine, 1-((E)-1-(4-methoxyphenyl)-5-trimethylsilyl-1-en-4-yn-3-ylidene)-2-phenylhydrazine, and 1-((E)-1-(toiphenyl-2)-5-phenylpent-1-en-4-yn-3-ylidene)-2-phenylhydrazine. The calculations were performed by the M06-2X/6-311+G(2df,2pd)//B3LYP/6-31G(d) method using the homodesmotic approach. The bond dissociation enthalpy is lower than 77 kcal/mol for all the cross-conjugated hydrazone derivatives under study. The experimental rate constants for the reactions of the derivatives with peroxyl radicals in chlorobenzene during the initiated styrene oxidation are comparable to those of aromatic amines and are in the range (1.1–2.5) × 10⁵ M⁻¹ s⁻¹. The stoichiometric inhibition coefficient depends on the structure of the derivatives and varies from 0.7 to 1.9. The inhibition is discussed within the framework of the radical mechanism.

For the first time, amorphous TiO₂ aerogels with a high specific surface area (420 m²/g) and low geometric density (~0.1 g/cm³) were obtained using epoxide-induced gelation in N,N-dimethylformamide. Impregnation of the resulting aerogels with aqueous solutions of H₂PtCl₆ and NaBH₄ followed by thermal annealing made it possible to obtain Pt/TiO₂ photocatalysts, which showed very high activity for titanium dioxide–based aerogels in the generation of hydrogen from aqueous alcohol solutions (~5 ({text{mmo}}{{{text{l}}}_{{{{{text{H}}}_{{text{2}}}}}}}) h^–1 g^–1).

In this work, steam-exfoliated graphitic carbon nitride was used as a promising basis for the development of photoactive materials for processes induced by visible light. Nanocrystalline cobalt(II,III) oxide, obtained by the solution combustion method followed by heat treatment of the reaction products, was used as a cocatalyst. Nanocomposite materials were prepared by joint ultrasonic treatment of graphite-like carbon nitride and cobalt(II,III) oxide in ethanol. The prepared series of samples with different weight fractions of the oxide (5–10 wt %) was studied by powder X-ray diffractometry, scanning electron microscopy, low-temperature nitrogen adsorption–desorption, and diffuse reflectance electron spectroscopy. The photocatalytic activity of the samples was evaluated in the oxidation of tetracycline hydrochloride. It was found that the rate constant of the photocatalytic reaction reached its maximum value with composites containing 7 wt % Co₃O₄ (k = 0.0104 min^–1). The photovoltaic response studies demonstrated that the presence of cobalt oxide in the samples can significantly decrease the rate of charge carrier recombination to increase the generated current by a factor of 1.2.

The photocatalytic activity of 2D/2D/0D heterostructures based on few-layer black phosphorus (FLBP) g-C₃N₄/FLBP/Co₂P in the reaction of photocatalytic hydrogen formation from an aqueous solution of triethanolamine under under visible light irradiation (400 nm) was studied for the first time. An original method for the preparation of the g‑C₃N₄/FLBP/Co₂P composite photocatalyst is proposed, which consists of the solvothermal synthesis of cobalt phosphide Co₂P nanoparticles, their immobilization on the surface of FLBP, and subsequent mixing of the FLBP/Co₂P heterostructure with g‑C₃N₄. The synthesized photocatalysts were characterized by physicochemical analytical methods (X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission microscopy, energy-dispersive X-ray spectroscopy). The hydrogen evolution rate in the presence of the g‑C₃N₄/FLBP/Co₂P heterostructure was 0.09 mmol ({text{g}}_{{{text{cat}}}}^{{ - 1}}) h^–1, which is 25 times higher than the same characteristic for the unmodified g‑C₃N₄ sample. The obtained numerical values of the photocatalytic activity are at the level of the literature values.

The kinetic modeling of high-temperature reforming of oxygen-free mixtures of methane with H₂, H₂O, CO, and CO₂ additives into synthesis gas with strong dilution with argon under conditions of variable temperature and the formation of microheterogeneous soot particles was carried out. Such mixtures are typical for biomass gasification products, in which H₂O, CO, and CO₂ additives act as oxidizing agents. A direct comparison of kinetic calculations with the results of published experiments in a flow reactor at temperatures of 1100–1800 K, atmospheric pressure, and a reaction time of 0.68 s was carried out. The yields of soot were calculated for all test mixtures and conditions. A comparison of the results of kinetic calculations and experiments made it possible to evaluate the effect of soot formation on the reforming of methane with the additions of H₂, H₂O, CO, and CO₂. The work analyzes two ways for carbon atoms to leave a reacting gas-phase system. The first way is the heterogeneous deposition of acetylene molecules from the gas phase onto the surface of the reactor with the subsequent formation of solid carbon, and the second way is the formation of microheterogeneous soot particles from nuclei in the gas phase. The paper compares the results of experiments in reflected shock waves and our kinetic calculations of the absolute concentration of CO for the process of methane oxidation in oxygen-free mixtures of methane and CO₂. Mixtures with various CH₄/CO₂ ratios, 90/10, 75/25, and 50/50, were studied at temperatures above 2200 K and atmospheric pressure. It has been shown that the agreement between the calculated and measured CO concentrations improved with increasing temperature and CO₂ fraction in the mixture.

The process of transformation of the size and shape of platinum precursor particles at all stages of the preparation of supported Pt catalysts from precursor solutions to supported metal particles was studied using small-angle X-ray scattering (SAXS). It has been established that primary Pt-containing particles of different shapes and sizes can be obtained on the surface of supports depending on the acid–base properties of the supports and the presence of a stabilizer in the precursor solution. It has been shown that the size and shape of the primary precursor particles are decisive for the dispersion of supported platinum catalysts during their further preparation.

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.