Reaction Kinetics, Mechanisms and Catalysis最新文献

In this study, the sol–gel synthesis of Ni-doped cadmium zinc aluminum ferrite Ni-doped Ni_xCd_0.8−XZn_0.2Al_0.3Fe_1.7O₄ (X = 0,0.4) nanoparticles and their photocatalytic activity for ciprofloxacin degradation under visible-light irradiation were investigated. The nanoparticles were characterized using XRD, FTIR, SEM, EDX, and BET analyses. XRD revealed cubic spinel structures with crystallite sizes of 39 (undoped) and 30 nm (Ni-doped). FTIR spectra showed peak shifts upon Ni doping, indicating Ni²⁺ ion substitution in the spinel lattice. SEM images showed that the nickel-free sample was porous and had larger, loosely packed grains, whereas the nickel-doped sample was denser and featured smaller, uniformly distributed grains. The Ni-doped sample exhibited a higher BET surface area (37.85 m²/g) and pore volume (1.836 cm³/g) than those of the undoped sample. The photocatalytic degradation of ciprofloxacin was significantly enhanced by Ni doping, achieving 97.88% in 60 min under visible light, which was attributed to the narrowed bandgap (2.1 eV), improved visible light absorption, and increased charge separation. Scavenger studies have identified hydroxyl radicals as primary reactive species. The addition of H₂O₂ (up to 6 mM) enhanced the degradation rate, but higher concentrations decreased the rate. The catalyst exhibited gradual deactivation upon reuse, with the degradation efficiency decreasing from 97.88 (first cycle) to 90.93% (fifth cycle), owing to loss, deactivation, and fouling.

The alumina particle supported Cu component catalyst, Cu/Al₂O₃, was prepared by equal volume wet impregnation and evaluated through degradation of maleic acid with catalytic wet peroxide oxidation (CWPO) in this work. It was found that the Cu/Al₂O₃ catalyst had an excellent CWPO performance. A total organic carbon (TOC) removal rate of 98% was reached under the optimized catalytic reaction conditions. Moreover, the effect of inorganic ions on CWPO was comprehensively evaluated using different acid and alkali. The alkali had an optimum effect on TOC removal rates, while acid had an inhibitory effect. A catalytic oxidation mechanism was proposed to illustrate the CWPO process of Cu/Al₂O₃ catalyst. The catalytic test results as well as the proposed mechanism can provide an insight into the influence mechanism of inorganic ions on CWPO.

This study aimed to produce the cost-effective mesoporous material “aluminum-modified MCM-41” using local Saidite clay for efficient removal of Malachite Green (MG) dye from an aqueous solution. Characterization of the products involved the use of X-ray diffraction (XRD), N₂ adsorption and desorption, and scanning electron microscopy (SEM). The X-ray diffraction analysis confirmed the successful synthesis of pure Al-MCM-41 without any impurities. The surface area of the sample was determined to be approximately 660 m²/g. Various parameters, including contact time, adsorbent dosage, initial pH of the solution, dye solution concentration, and temperature, were taken into account. At a temperature of 298 K, the maximum adsorption capacity for MG was found to be 55 mg/g. Both adsorption isotherm and kinetic models were examined, revealing that the Langmuir model best described the adsorption phenomenon. Furthermore, the adsorption kinetics followed the pseudo-second-order kinetic model, demonstrating a high correlation coefficient (R² = 0.99). Additionally, the study discussed the mechanical interaction between the removal of MG and Al-MCM-41.

Catalyst preparation, reaction process conditions and kinetics of the selective hydrogenation of fatty acid methyl esters (FAME) over a noble metal catalyst were studied. Two catalysts were prepared by impregnation of γ-Al₂O₃ with Ru (1% mass content) as active metal and Sn and B as modifiers (2% mass content), and with different Sn/Ru ratios of 2 and 4. FAME derived from biomass, an environment friendly raw material, was used for the preparation of fatty alcohols by selective hydrogenolysis of the ester group to an alcohol group. The results were analyzed with a simple kinetic model using lumped pseudocomponents. When comparing the two catalysts it was found that the most effective catalyst for producing oleyl alcohol was the one with a Sn/Ru ratio of 2, RuSn2–B. The maximum production of alcohols and alkanes was achieved with this catalyst at 290 °C. At 270 °C a lower production of alkanes was obtained but with a similar yield of alcohols. Both reaction conditions and catalyst composition were found to be important factors influencing alcohol production. Two types of active sites were identified on the studied catalysts: the unmodified Ru⁰ metal for dissociating hydrogen and the modified metal, (Ru⁰–(SnO_x)₂, for adsorbing the C=C carbons. RuSn2–B seemingly exhibited an appropriate balance of these sites. The kinetic model included the reactions of esters, hydrogen, alcohols and deoxygenated hydrocarbons. These were studied with lumped variables with no distinction of individual specific molecules. In spite of this, the model provided a very good fit of the experimental data indicating that the reaction is rather insensitive to secondary features like carbon chain length or group positions.

The upgrading of pyrolysis deoxygenation of polyester/viscose fibers was examined in this paper utilizing montmorillonite (MMT) catalysts with varying ratios and amounts of tungsten-manganese bimetallic. The temperature-programmed desorption of NH₃ (NH₃-TPD) revealed that after tungsten-manganese bimetal loading, MMT formed novel acidic sites, resulting in a considerable rise in total acidity. The maximum aromatics yield (73.10%) was achieved by the MMT with a bimetal loading of 10 wt%, the yield of monocyclic aromatic hydrocarbons (MAHs) was highest at 40.38%, while the yield of polycyclic aromatic hydrocarbons (PAHs) was lowest. The MAHs yield dramatically dropped at 15 wt% and 20 wt% bimetal loading. The application of a moderate load has the potential to facilitate the generation of MAHs, whilst an excessive load can readily facilitate the development of PAHs. The acid equilibrium of MMT was enhanced following the application of varying ratios of tungsten-manganese bimetal loading. When the ratio of bimetal load was 1:1, a significant synergistic impact was seen, resulting in a substantial enhancement of the catalyst regulation performance on MAHs and PAHs. Specifically, the catalyst exhibited a tendency to generate a higher proportion of useful MAHs (40.38%) while simultaneously reducing the production of PAHs (32.72%). This phenomenon can be attributed to the appropriate pore structure and the equitable distribution of Lewis acid and Brønsted acid sites within the pores.

This work aims to examine the application of ZnO/Curcumin nanocomposite materials, in which curcumin (natural dye) is used as a photosensitizer in the photocatalytic degradation of methylene blue (MB) under visible light irradiation. The ZnO/x% curcumin nanocomposite materials (with x = 3, 5, 7, 10 and 20) are prepared by the wet impregnation method. These nanocomposite materials are characterized using various techniques; including Fourier transform infrared spectroscopy, X-ray diffraction, ultraviolet–visible spectroscopy and scanning electron microscopy. Optimal MB degradation of ~ 99% was obtained with a concentration of 0.5 g L⁻¹ of 5% curcumin/ZnO nanocomposite catalyst material, at natural pH and initial MB concentration of 10 mg L⁻¹ for 90 min exposure to visible light irradiation. The kinetic indicates that the Langmuir–Hinshelwood (L–H) model is well adapted to the experimental data. Pseudo-first order kinetics were obtained with a rate constant (k) and half-life time (({t}_{1/2})) of 0.0423 min⁻¹ and 16 min. The significant improvement in the photocatalytic properties of ZnO under visible light irradiation induced by the addition of curcumin as a photosensitizer could be due to the increase in the concentration of reactive radical species in the solution, such as superoxide (({text{O}}_{2}^{ cdot - })) and hydroxyles (({text{OH}}^{ cdot })).

Cu-ZSM-5 (Cu-Zeolite Socony Mobil-five) catalysts with different Cu loadings were prepared by ion exchange method. Different Ce loadings were coated on the surface of 0.1Cu-ZSM-5 to form CeO₂-Cu-ZSM-5 catalysts. Cu could improve the NH₃-SCR activity and broaden SCR temperature window. 0.1Cu-ZSM-5 showed the best catalytic performance (above 90%) in 200–400 ℃. 30% CeO₂-Cu-ZSM-5 catalyst was able to increase the NO conversion in the low-temperature region and keep the activity unchanged in the high-temperature region. CeO₂ that was coated on the catalysts preferentially reacted with SO₂, enhancing the excellent anti-sulfur poisoning performance. TPD, TPR, and XPS results showed that the synergistic effect of Ce and Cu increased the acidic sites and improved the redox capacity of catalysts. According to in situ DRIFTS spectra, Cu-ZSM-5 catalyst followed the Langmuir–Hinshelwood mechanism, and 30% CeO₂–0.1Cu-ZSM-5 catalyst followed not only the Langmuir–Hinshelwood mechanism but also the Eley–Rideal mechanism.

In this study, the synthesis, characterization, and photocatalytic activity of zinc-doped cadmium aluminum ferrite Zn_xCd_X−1Al_0.1Fe_1.9O₄ (X = 0,0.3) nanoparticles were investigated for the degradation of atrazine. The nanoparticles were synthesized via a sol–gel method, and their structural, morphological, and optical properties were characterized using various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and UV–Vis diffuse reflectance spectroscopy. The photocatalytic activity of the synthesized nanoparticles was evaluated under visible-light irradiation, and the influence of various parameters, such as Zn doping concentration, initial atrazine concentration, pH, temperature, catalyst dose, light intensity, and addition of hydrogen peroxide (H₂O₂), was investigated. The results demonstrated a significant enhancement in atrazine degradation with Zn-doped cadmium aluminum ferrite, achieving a removal efficiency of 93% compared with 75% for undoped cadmium aluminum ferrite at normal conditions. Scavenger analysis suggested that hydroxyl radicals (OH˙) played a crucial role in the photodegradation process. These findings contribute to the development of efficient and sustainable photocatalysts for the degradation of atrazine and other organic pollutants.

In this study, we investigated the photocatalytic degradation of Congo red dye using zinc-doped cadmium manganese aluminum ferrite nanoparticles (Zn_xCd_0.8−xMn_0.2Al_0.1Fe_1.9O₄, X = 0, 0.3). Ferrite catalysts were synthesized via a sol–gel method and extensively characterized to understand the impact of Zn doping on their structural, morphological, and textural properties. FTIR, SEM, EDX, and BET analyses confirmed that Zn doping modified the characteristics of the catalyst. Zn doping decreased the crystallite size and lattice parameters, increased the FWHM and density, and shifted the metal–oxygen bond vibration peaks. The SEM images showed that Zn doping refined the particle size and improved the morphology, confirming the incorporation of Zn. The BET analysis revealed that Zn doping enhanced the surface area, pore volume, and pore radius. The undoped photocatalyst possessed a bandgap of 2.8 eV, while Zn-doping led to a narrower bandgap (2.6 eV), consequently enhancing visible light absorption. The Zn-doped catalyst achieved 93.12% Congo red degradation at pH 7, 30 °C, 80 min and concentration of Congo red dye 10 ppm, significantly outperforming the undoped catalyst (62.45%). Zn doping improved charge separation and promoted the generation of reactive oxygen species (ROS), leading to enhanced photodegradation efficiency. Scavenger studies confirmed the crucial role of hydroxyl radicals in the degradation process. Furthermore, the Zn-doped catalyst maintained an 81.03% degradation efficiency even after five consecutive cycles, indicating promising recyclability. These findings highlight the potential of Zn-doped cadmium manganese aluminum ferrite as an efficient and stable photocatalyst for remediation of Congo red-contaminated wastewater.

The dry reforming of methane (DRM) was conducted using a Ni-SiO₂ catalysts. It was evaluated the catalyst’s stability within the temperature range of 973–1033 K under low spatial time conditions (kinetic regime) in the reactor. The catalyst deactivated more rapidly at high temperatures, contrary to the prediction based on chemical equilibrium calculations. To understand this behavior, it was investigated the impact of reactor operating conditions by simulating the reactor using a pseudo-homogeneous model and comparing the results with the chemical equilibrium prediction. The simulations revealed that, at high spatial times (W/F_CH4), the reactions considered for the DRM process closely approach equilibrium. In contrast, at low spatial times, the reactive system deviates from chemical equilibrium, with the water gas shift and disproportionation of CO being the most favored. This results in increased coke production, which leads to faster catalyst deactivation. The effect is attributed to the kinetic inhibition of CO₂ adsorption, hindering the activation of this molecule at high spatial time. The spatial time in the reactor, whether high or low, strongly depends on the intrinsic catalytic activity of the catalyst. Thus, when studying catalytic solids, the operating conditions of the reactor should be taken into account to avoid erroneous interpretations of the experimental data when evaluating their performance (for example, catalyst selectivity or resistance against deactivation by coke).