Kinetics and Catalysis最新文献

A series of heterogeneous catalysts for peroxide oxidative desulfurization and denitrogenation based on imidazolium phosphomolybdates with different cation structures and acidic properties was prepared. Thiophene, dibenzothiophene, methyl phenyl sulfide, and pyridine were used as model substrates. The composition and structure of the initial ionic derivatives and heterogeneous compositions based on them were determined using a number of physicochemical methods. It was found that the structure of the imidazole cation affected the stability of the heteropolyanion, the distribution of an active phase on the surface of silica gel, and, as a consequence, the efficiency in catalysis. The catalysts were tested in solutions containing either a substrate or a mixture of nitrogen- and sulfur-containing compounds.

This study employed detailed chemistry in conjunction with a zero-dimentional model (senkin code) to numerically investigate the ignition delay times of ternary biodiesel surrogate fuels (comprising n-heptane/methyl-decanoate/methyl-9-decenoate in an 80/10/10% molar ratio) blended with ethanol at ratios of 5, 10, 15 and 20%. Equivalence ratios covered the lean (Φ = 0.5), stoichiometric (Φ = 1.0) and rich (Φ = 1.5) mixtures with temperatures ranging from 700 to 1000 K and pressures from 20 to 40 bar. The primary objective of this work was to assess and quantify the role of chemical and physical (dilution and thermal) effects resulting from ethanol enrichment on the ignition delay times of these blended fuels. The modeling results indicated that ethanol addition had a distinctly different effect on the biodiesel reactivity in the low- and intermediate-temperature regimes. Below 900 K, ethanol addition decreased reactivity, whereas the opposite trend was observed in the temperature range of 900–1000 K. Irrespective of the ethanol ratio, a significant reduction in ignition delay times occurred upon increasing chamber pressure and equivalence ratio, with this phenomenon being more pronounced at higher chamber temperatures. Finally, it was found that under all modeling conditions, the physical effect of ethanol enrichment was less pronounced than the chemical one.

Using the properties of the Lambert function we review the analytical solutions of the Michaelis–Menten (MM) kinetics and other related models. We derive several quantities of interest such as the half-life and the area under the curve (AUC). The effect of varying the parameters in the Beal–Schnell–Mendoza solution and its asymptotic time behavior were analyzed. The Maclaurin expansion of the time evolution of substrate concentration up to sixth order is presented. These expressions were tested on the well-known problem of ethanol elimination from the human body and excellent agreement was found. In addition, a closed-form solution for the derived problem that combines simultaneously MM and zeroth-order kinetics is derived. This problem was solved by a suitable transformation of variables that casts the original differential equation into a functionally equivalent MM problem with termination time. To finish, analytical solutions for the MM process in parallel with zeroth- and first-order kinetics are presented here as well. We checked all equations against the numerically exact solution of the corresponding differential equation and perfect agreement was found in all cases.

The specific surface area of attapulgite was significantly enhanced (from 128 to 212 m²/g) by its purification with sodium hexametaphosphate and nitric acid. Subsequently, an acid modification method was employed to prepare a coated attapulgite cordierite honeycomb with a specific surface area approximately 39 times larger than that of the bare cordierite honeycomb. SEM images showed that the surface of the cordierite was rough and uneven, with the attapulgite filling the large pores on its surface, forming a “nail-like” interaction between the coating and the carrier. After loading the catalyst, no significant mass loss was observed after 1 h of ultrasonic testing, indicating good adhesion stability of the coating. Furthermore, under test conditions of GHSV (Gas Hourly Space Velocity) = 10 000 h^–1 and a toluene concentration of 1500 ppm, the prepared integrated catalyst exhibited excellent activity for the catalytic oxidation of toluene, with T₅₀ and T₉₀ values of 261 and 290°C, respectively, suggesting broad application prospects.

A Pt(1.5%)Sn(0.25%)/Al₂O₃ catalyst synthesized by the sequential impregnation of γ-alumina with aqueous solutions of hydroplatinic acid and tin chloride has been characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The kinetic laws governing methylcyclohexane dehydrogenation to toluene and hydrogen in a tubular flow reactor in the isothermal mode at atmospheric pressure have been studied, while varying the reactant concentrations, contact time, and temperature. An empirical mathematical model of kinetics, which includes three adsorption forms of a bifunctional active site, has been developed. The model adequately describes the test data for the forward and reverse reaction routes.

The direct production of higher alcohols from syngas in a single step remains a great challenge. In this work, a series of K and Ni promoted Mo₂C/Al₂O₃ catalysts were prepared by impregnation method to enhance the selectivity of Mo₂C-based catalysts for the one-step conversion of syngas to higher alcohols. The catalysts were continuously tested under the following conditions: 300°C, 3.0 MPa, velocity—11.50 ({text{Lg}}_{{{text{Mo}}}}^{{ - 1}}) h^–1, H₂/CO ratio of 2. The catalysts promoted with K and Ni demonstrated the highest total alcohol selectivity of 67.7%. Moreover, the selectivity for total C₂₊ alcohols reached as high as 56%, with 37% being ethanol. X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) characterization data reveal that K can promote the crystallinity of β-Mo₂C, lower the catalyst reduction temperature and increase the proportion of high-valent Mo on the catalyst surface. In addition, adding Ni as a promoter to the KMo₂C/Al₂O₃ catalyst can generate a synergistic effect to further enhance the catalytic activity and the selectivity of higher alcohols.

Nitrous oxide (N₂O) is a long-lived stratospheric ozone-depleting substance with an atmospheric lifetime of 116 years. It is also a greenhouse gas with a global warming potential value of about 310. Due to its high kinetic stability and thermal decomposition temperature exceeding 1000°C, the treatment and recovery of nitrous oxide pose significant engineering and climate challenges. In this study, we introduce a Cu–Fe oxide catalyst that demonstrates efficient and low-temperature conversion of N₂O to N₂ using readily available reductant CO. The oxide catalyst was synthesized by a solvothermal method and a “from bottom to top” technique. Characterizations by X-ray diffraction (XRD), CO temperature-programmed desorption (C-O‑TPD), scanning electron microscopy (SEM), and BET indicate that the catalyst with weaker CO adsorption sites, fewer strong CO adsorption sites, suitable particle size, good dispersion and high specific surface area performs excellent reaction activity in the reduction of N₂O to N₂ by CO. The active site of Cu is stronger, and the addition of Fe can promote dispersion of the Cu active site and increase the exposure to the active site. A new approach has been proposed to address nitrous oxide emissions, a greenhouse gas with high thermodynamic stability, in the chemical industrial process that generates nitrous oxide as a byproduct.

Volatile organic compounds (VOCs), play a crucial role as precursors of ozone (O₃) and secondary organic aerosols, making them significant air pollutants. Efforts to effectively eliminate ethyl acetate (EA), a typical VOC in many industrial processes, has attracted significant attention worldwide. In this study, a catalyst consisting of MgAl₂O₄ spinel prepared via the sol-gel method was adopted to support MnO_x by incipient wetness impregnation for complete catalytic oxidation of EA. The prepared catalysts were characterized by XRD, SEM, TEM, BET, XPS and H₂-TPR. It was found that the calcination temperature of the support is crucial for the catalytic activity. The optimal calcination temperature of the support is found to be 800°C, resulting in a perfect MgAl₂O₄ spinel phase and a crystalline size of 8.3 nm. The optimized MnO_x/MA-800 displayed high catalytic activity (T₉₅ = 240°C) and stability due to its high reduction ability and high atomic ratios of Mn⁴⁺/Mn³⁺ and O_ads/O.

Two novel Ru(II)-phenanthroline derivatives complexes, Ru-1 and Ru-2, were synthesized and characterized. The key distinction between Ru-1 and Ru-2 lies in their ligands: L1 (2-hydroxy-5-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl) benzoic acid) and L2 (2-hydroxy-3-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)benzoic acid). In L1, the –OH group is located in the para-position, while in L2, it resides in the ortho-position. Subsequently, Pt/TiO₂ and Ru-1/Pt/TiO₂ (and Ru-2/Pt/TiO₂) composites were prepared using photo-deposition and impregnation methods, respectively. The Ru-1/Pt/TiO₂ and Ru-2/Pt/TiO₂ composites were thoroughly characterized using various techniques, including ultraviolet-visible spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), fluorescence spectroscopy (FL), cyclic voltammetry (CV) experiments, and other relevant techniques. Photocatalytic hydrogen production systems were established by employing Ru-1/Pt-TiO₂ and Ru-2/Pt-TiO₂ as photocatalysts and ascorbic acid (H₂A) as a sacrificial reagent. The results demonstrated that the maximum hydrogen production reached 1461 μmol (Ru-1/Pt/TiO₂) and 843 μmol (Ru-2/Pt/TiO₂) under optimized conditions with 20 mg of composite photocatalyst, 0.3 mol L^–1 of H₂A, and pH 4, within 4 h of irradiation (λ > 420 nm). Correspondingly, the photocatalytic hydrogen production rates were 18 267 and 10 523 μmol g^–1 h^–1, respectively. Mechanism studies revealed that electrons flow from the highest occupied molecular orbital (HOMO) of Ru-1 to the conduction band (CB) of TiO₂, subsequently combining with H⁺ on the surface of the Pt metal nanoparticles to generate hydrogen gas. The holes on the lowest unoccupied molecular orbital (LUMO) of the photosensitizer are oxidized by H₂A, thereby regenerating the activity of the composite catalyst by restoring the photosensitizer.

Photocatalytic and antibacterial properties of PbS:Ag (PA) and rGO-blended PbS:Ag (rPA) nanoparticles (NPs) have been compared and reported in this paper. Chemical precipitation and one-pot synthesis methods were used to synthesize NPs of PA and rPA. X-ray diffraction (XRD) studies reveal a cubic crystal structure for both samples, with preferential growth along the (200) plane. Crystallite sizes were 55 and 41 nm for PA and rPA, respectively. Scanning electron microscopy (SEM) images of rPA revealed clustered grains. Both samples exhibited Pb–S bands in Fourier-transform infrared spectroscopy (FTIR) studies. Near band edge emissions occurred at 504, 520, 539 and 595 nm for both PA and rPA. The inclusion of rGO into PA led to lattice misfit, crystal growth disorders, and increased grain boundary scattering. This series of structural disruptions contributed to a reduction in the photoluminescence (PL) intensity for the rPA composite. A higher degradation efficiency of 95.4% was achieved for the rPA catalyst against Rhodamine B dye under visible light. The antibacterial activity of PA is increased with rGO inclusion due to increased generation of reactive oxygen species (ROS).