Kinetics and Catalysis最新文献

Catalytic nonoxidative propane dehydrogenation (PDH) is the purposeful and most economical route to propylene production. The development of new PDH catalysts that can compete with existing commercial platinum and chromium catalysts is a major challenge for the progress of this technology. In the present study, GaO_x-based catalysts (Ga₂O₃ in bulk form or deposited on oxide supports such as SiO₂, Al₂O₃, TiO₂, and ZrO₂) were prepared and their catalytic performance in the PDH was examined. It was shown that the activity of the catalysts depends on the support selected. The best results have been obtained with gallium oxide supported on alumina. The catalytic properties of this material were further improved by doping with lanthanum. PDH reaction catalyzed by La–Ga/Al₂O₃ at 600°C at a gas hourly space velocity (GHSV) of 7500 mL h⁻¹ ({text{g}}_{{{text{cat}}}}^{{ - 1}}) (propane/N₂ = 1/10) provided ca. 30% propane conversion with 95% propylene selectivity. The effect of the La-doping on the properties of bulk and supported Ga₂O₃ were therefore studied by XRD, Raman and ATR-FTIR spectroscopies, HR-TEM, and low-temperature nitrogen adsorption techniques, which showed that La-doping contributes significantly to dispersion of gallium, diminishes crystallinity of the alumina support and increases the specific surface area of the catalyst.

Rice husk is a byproduct of rice milling, containing a high percentage of silica (silicon dioxide). Rice husk ash (RHA), produced from rice husk, was used as a support for 12-phosphotungstic acid. It is a practical and potentially beneficial approach in catalysis. A series of supported catalysts with 12-phosphotungstic acid (20–40 wt % of H₃PW₁₂O₄₀), immobilized on rice husk ash via impregnation using the initial moisture content method, were prepared. The catalysts were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis and scanning electron microscopy (SEM) for annotation of the catalytic behavior. The catalytic activity of the H₃PW₁₂O₄₀/RHA catalyst was evaluated in the synthesis of n-butyl acetate. The catalyst with 30 wt % H₃PW₁₂O₄₀, immobilized on rice husk ash, demonstrated the highest conversion of acetic acid. The reactions were carried out in a batch reactor. The highest conversion of 84.2% was attained under optimal conditions: temperature of 120°C, an acid-to-alcohol mole ratio of 1 : 2, agitation at 400 rpm, and catalyst loading of 1.5 wt % over 180 min. Additionally, the catalyst was also assessed to determine its stability and reusability.

Interfacing two semiconductors for heterojuctions construction has been considered as an effective way to facilitate electron-hole separation, thus improving the photocatalytic activity. In this paper, PCN-224/g-C₃N₄ heterojunction was constructed by PCN-224 and g-C₃N₄ using a solvothermal method. Transmission electron microscopy (TEM) images reveal a well-matched, smooth interface between PCN-224 and g-C₃N₄, demonstrating the successful formation of a tight junction. Photoelectric performance tests confirm that the heterojunction significantly enhances the light absorption capability within the visible range and improves the efficiency of electron-hole separation. Herein, the PCN-224/g-C₃N₄ heterojunction exhibited excellent photocatalytic activity in both disinfection and organic pollutant degradation. Under visible light irradiation (λ > 420 nm) for 3 h, it completely degraded phenol and effectively inactivated E. coli. In the photocatalytic process, electrons migrate from the conduction band of g-C₃N₄ to PCN-224, while holes transfer from the valence band of PCN-224 to the valence band of g-C₃N₄, thereby generating ({text{O}}_{2}^{{bullet - }}) and h⁺ radicals. These generated radicals effectively oxidize and degrade phenol.

The catalytic activity of LaFe_{1 – x}Co_xO₃ perovskites obtained by the Pechini method was studied in reactions of high-temperature decomposition of N₂O, oxidation of CH₄ and CO. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), adsorption and temperature-programmed hydrogen reduction (H₂-TPR). The obtained single-phase solids with a specific surface area (S_BET) of 6.1–9.7 m²/g are porous aggregates of 10 nm to 1 micron in pore size, consisting of dendrite-like agglomerates. It has been shown that the increase in Co content leads to increase of the amount of weakly bound oxygen in perovskites. Analysis of the relationship between the activity of LaFe_{1 – x}Co_xO₃ perovskites and the amount of weakly bound oxygen revealed a good correlation for the entire range of compositions only for the N₂O decomposition reaction; a limited correlation (up to x = 0.6) for the CO oxidation reaction and the absence of such a correlation for the CH₄ oxidation reaction. The influence of key stages of reaction mechanisms affecting activity is discussed. The advantage of using the Pechini method for the preparation of high active N₂O decomposition catalysts was revealed.

The removal of hazardous pollutants, such as organic compounds and azo dyes like rhodamine B (RhB) and methylene blue (MB), from industrial wastewater is essential for safeguarding public health. Copper sulphide (CuS)-based nanostructures in particular have drawn interest due to their potential for environmental uses, such as photocatalytic degradation. CuS nanostructures have remarkable optical and structural qualities that make them useful for a variety of applications, including photovoltaics and photocatalysis. This study looked into what gallium doping does to the optical, photocatalytic, structural, and morphological properties of Ga-doped CuS nanostructures that were made by chemical solution deposition. The films were examined using sophisticated characterisation methods, such as fluorescence intensity measurements, Raman spectroscopy, FTIR, X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis spectroscopy. According to the findings, photocatalytic degradation of MB and RhB dyes under visible light was improved by increasing the Ga concentration; the best efficiency was obtained at 8 wt % Ga doping. Ga-doped CuS nanostructures are highlighted as promising materials for environmental applications like water purification because of this enhancement, which is ascribed to changes in crystal structure, increased surface area, and improved charge separation. However, as performance usually declines beyond the ideal level, the photocatalytic activity of CuS–Ga (>8 wt %) should also be examined to identify the ideal doping density.

A highly dispersed Ni₂P/Al₂O₃ catalyst was prepared by phosphidating nickel sulfide supported on Al₂O₃ using a triphenylphosphine (TPP) solution. The synthesis of Ni₂P/Al₂O₃ was successfully achieved at a phosphidation temperature of 523 K, resulting in Ni₂P particles that were well-dispersed on the Al₂O₃ support, with an average particle size of approximately 8.7 nm. The resulting Al₂O₃-supported Ni₂P catalyst demonstrated exceptional activity in the hydrotreating of model diesel, significantly outperforming traditional Ni₂P catalysts synthesized via the temperature-programmed reduction (TPR) method. This work presents a straightforward approach for synthesizing transition metal phosphide catalysts for hydrotreating using sulfides as precursors.

Pd nanoparticles were synthesized by reducing PdCl₂ in aqueous or alcoholic solutions in the presence of NaOH or hydrazine hydrate, as well as without them. The palladium powder samples were characterized by X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS) methods. The size of the synthesized Pd nanoparticles varied from ~8 to 28 nm. They were used as a base for the development of catalytically active electrode materials for use in solid polymer fuel cells. The most electrochemically active and stable catalytic electrode materials were determined. Such materials are relevant for use in hydrogen-air fuel cells as an alternative to hydrocarbon fuel.

The article describes a modifying effect of 2,6-dimethyl pyridine (lutidine) in propylene polymerization reactions with a pseudo-homogeneous catalyst system Ti(Oi-C₃H₇)₄–Al(C₂H₅)₂Cl/Mg(C₄H₉)₂. This catalyst system is a convenient model for the analysis of modifier effects (effects of “external donors”) in supported Ziegler–Natta polymerization catalysts. A combination of IR, ¹³C NMR and GPC data for polypropylene prepared with this catalyst in the presence of 2,6-dimethyl pyridine shows that the modifier converts a part of stereo-aspecific active centers (the centers producing atactic polypropylene), into syndiospecific centers.

The novel solid acid based on hypercrosslinked polymer (HCPs–SO₃H) was synthesized via the direct copolycondensation of 4,4'-bis(chloromethyl)-1,1'-biphenyl (BCMBP) and naphthalene and sulfonation using chlorosulfonic acid. The polymer structure could be adjusted by naphthalene. The extremely high surface area of 1044 m²/g and mesoporous texture facilitate mass transfer of reagents, and special rigid aromatic ring framework ensured the expressed hydrophobicity of the surface. The plentiful aromatic rings provided sufficient sulfonation sites, and after sulfonation acidity over 3.4 mmol/g. HCPs–SO₃H showed high activity for ethyl levulinate (EL) synthesis from furfuryl alcohol (FA) with maximum yield 90.5%. Also, the efficient procedure for biodiesel synthesis from waste oil (WO) was developed using the HCPs–SO₃H. Both the free fatty acids (FFAs) and glycerides were conversed to methyl esters of fatty acids (biodiesel) with total yield over 99%. Therefore, the high surface area, high acidity and special rigid aromatic ring framework were the key features for the high activities of novel HCPs–SO₃H in organic synthesis.

Solid waste management, particularly the treatment of plastic waste, is a global challenge. This study investigates the pyrolysis characteristics of polypropylene (PP), polyethylene (PE), polystyrene (PS), and their mixture (MP). Thermogravimetric analysis (TG/DTG), differential thermal analysis (DTA), and gas chromatography–mass spectrometry (GC–MS) with a single quadrupole mass spectrometer were employed to analyze the driving factors, pathways, phenomena, mechanisms, and products of the pyrolysis process for these four plastics. The kinetic parameters of the pyrolysis and co-pyrolysis processes were calculated using the Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Starink, and Vyazovkin non-modeling methods, and the Fraser–Suzuki deconvolution method was applied to analyze the pyrolytic characteristics of the components in mixed plastics (MP). Based on the activation energy analysis results, the Master-plots method was used to obtain the pyrolysis mechanism functions for the four plastics. The analysis revealed that MP exhibited synergistic effects during co-pyrolysis. Heating rate experiments conducted under different pressures demonstrated that higher pressures promote secondary reactions such as the polymerization and condensation of olefins in the products. These findings indicate that MP has the potential for higher pyrolysis efficiency. The findings are expected to provide valuable insights for optimizing recycling technologies and enhancing the sustainability of plastic waste management.