Reaction Kinetics, Mechanisms and Catalysis最新文献

In this paper, α-MnO₂–S, α-MnO₂–Ac, α-MnO₂–Cl and α-MnO₂–N have been prepared via redox reaction with potassium permanganate as oxidant, manganese acetate, manganese nitrate, manganese chloride and manganese sulfate as reducing agents to regulate the microstructure of α-MnO₂, and its catalytic oxidation performance of toluene was evaluated. Results showed that the α-MnO₂–Ac catalyst exhibited the highest catalytic activity (T₉₀ = 226 °C) for toluene oxidation. Compared with other Mn-based oxides, the α-MnO₂–Ac has more surficial oxygen vacancies and higher specific surface area, as well as excellent low temperature reduction performance, which is the reason on its remarkable activity for toluene oxidation. In addition, α-MnO₂–Ac catalyst presented good stability and repeatability during 50 h durability test under water vapor.

The nickel-aluminum composite oxide was synthesized via the co-precipitation and roasting method, and then we explored the profound effect of reduction temperature during activation on formation and evolution of the Ni/Al₂O₃ catalysts. Hereon, the hydrogenation of dimethyl terephthalate (DMT) to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) was a probe reaction for the investigation into the structure–activity relationship of the Ni/Al₂O₃ catalyst. This study leveraged techniques such as TEM, H₂-TPR, XPS, H₂-TPD to examine the impact of reduction temperature on the catalyst’s structure and hydrogenation capabilities. The findings demonstrated that as the reduction temperature increased, so did the reduction degree of Ni²⁺ in the catalyst and the H₂ adsorption sites. However, excessively high reduction temperatures can lead to the sintering of the Ni⁰ particles, thereby increasing grain size, and the optimal reduction temperature was determined to be 550 °C. Smaller grain sizes of the Ni⁰ particle were particularly suitable for saturation hydrogenation of benzene ring. A DMT conversion of 100% and a DMCD selectivity of 91.3% were obtained over the optimized Ni₂Al₁-550 catalyst under the moderate conditions of 150 °C and 5 MPa.

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In this study, the adsorption of Methylene Blue (MB) and Methyl Orange (MO) dyes from aqueous solutions onto both metallic Ag NPs and Cu NPs and bimetallic Ag/Cu NPs obtained from the extract of Helichrysum arenarium, an aromatic plant, by green synthesis method was investigated and equilibrium isotherms and kinetic models were determined. The adsorption parameters, such as pH, adsorbent amount, contact time and initial concentration were optimized. The most successful removal for MO was achieved with Ag/Cu NPs at 76.9% under optimum conditions (20 mg/L MO, 20 mg Ag/Cu NPs, 60 min contact time, pH 2), while that for MB was achieved with Ag NPs at 82.7% under optimum conditions (20 mg/L MB, 20 mg Ag NPs, 60 min contact time, pH 4). Moreover, the adsorption data were modelled by Langmuir and Freundlich adsorption isotherms and Langmuir adsorption was found to be the most appropriate adsorption isotherm model for both MB and MO. Furthermore, while the pseudo-first-order reaction kinetic model was found to be the most suitable for MO dye, the pseudo-second-order reaction kinetic model was found to be the most suitable for MB dye. Based on the experimental results, bimetallic Ag/Cu NPs can be considered as effective, economic, and alternative adsorbent based on the maximum adsorption capacities which were found to be 191.696 mg/g for MO and 374.001 mg/g for MB. The highest efficiency of bimetallic Ag/Cu NPs is due to the properties of both Ag NPs and Cu NPs.

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In the present study, the influence of ZSM-5 zeolite structure on the catalytic properties and hydrothermal stability is investigated in detail. By XRD, N₂ adsorption/desorption, NH₃-TPD, SEM, ²⁷Al MAS NMR, XPS, DR-UV and ZLC characterizations, it has been confirmed that a nano-sized ZSM-5 (SZ) exhibits the higher external surface area (more pore mouths) and shorter pore channels than the micro-sized ZSM-5 (CZ), which contributes to the better diffusivity of reactants/products resulting in better accessibility of acid sites in channels by reactants and less secondary reactions of products. Furthermore, another advantage of SZ sample is reflected in the less Al pairs and more uniform Al distribution, which is favorable to the hydrothermal stability of zeolite. Especially, the smaller particle size of SZ can also improve the diffusion efficiency of doping P species into the interior pore, which further increases the hydrothermal stability of P/SZ sample due to the strengthened P-Al interaction. As a result, the P/SZ catalyst exhibits a simultaneous increase in both catalytic activity and hydrothermal stability in the catalytic cracking of naphtha compared to the P-modified CZ.

This study presents the design and optimization of copper(I) oxide (Cu₂O) thin films as electrocatalysts for glycerol electro-oxidation in alkaline environments. Cu₂O films were synthesized via electrodeposition on copper substrates using a citric acid-based electrolyte, chosen for its low toxicity and complexing properties. The study systematically optimized key deposition parameters such as temperature (55–75 °C), stirring rate (0–300 r min⁻¹), scan rate (10–100 mV s⁻¹), and precursor concentration (0.05–0.07 mol L⁻¹) using Response Surface Methodology (RSM) coupled with a Box-Behnken Design (BBD). The optimized conditions (75 °C, 300 r min⁻¹, 55 mV s⁻¹, 0.06 mol L⁻¹) resulted in the formation of a homogeneous, adherent Cu₂O film with a thickness of 420.69 nm, predicted by a statistically validated quadratic model (R² = 0.9768). Structural analysis by X-ray diffraction (XRD) confirmed the formation of pure Cu₂O in the cubic cuprite phase. Optical microscopy revealed a smooth and uniform surface, which is vital for electrocatalytic applications. Electrochemical testing showed that the Cu₂O film stabilized the open circuit potential at -0.1150 V vs. Ag/AgCl, indicating surface passivation. Cyclic voltammetry (CV) in an alkaline glycerol solution (0.5 mol L⁻¹) exhibited two oxidation peaks at − 0.01 V and + 0.23 V vs. Ag/AgCl, confirming the electrocatalytic activity of the Cu₂O film. Chronoamperometric measurements at + 0.2 V vs. Ag/AgCl for 40 min revealed a stable current density (~ 2.41 mA) for the thicker film, indicating improved electrocatalytic performance due to a larger electroactive surface area. These results demonstrate that Cu₂O thin films, synthesized under optimized conditions, exhibit promising catalytic activity for glycerol electro-oxidation, offering an alternative to noble metal-based catalysts.

This study investigated the adsorption performance of LaFeO₃/g-C₃N₄ (LFO/g-CN) composite material for the removal of Orange G (OG) dye from aqueous solutions. The LFO/g-CN composite, prepared by wet impregnation method from LFO phase and g-CN compound, was characterized using various techniques including Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), and Brunauer–Emmett–Teller (BET) surface area analysis. BET results revealed a significant increase in surface area from 3.7 m² g⁻¹ for LFO to 51 m² g⁻¹ for the LFO/g-CN composite. The adsorption efficiency was optimized by examining different factors affecting the adsorption process including adsorbent amount, initial pH, solution temperature, contact time and initial OG dye concentration. The maximum removal percentage of OG onto LFO/g-CN material was found to be 72% at pH 2 and 55 °C, using an adsorbent amount of 150 mg and initial OG dye concentration of 10 mg L⁻¹ during a contact time of 180 min. The pseudo-second Order (PSO) kinetic and Langmuir isotherm models accurately described the adsorption of OG on the LFO/g-CN composite. Thermodynamic analysis confirms that the adsorption process is spontaneous ((Delta {G}^{circ }hspace{0.17em})< 0) and endothermic (({Delta H}^{circ }) > 0). This information contributes to a better understanding of LFO/g-CN as an efficient adsorbent for dye removal, offering potential applications in wastewater treatment at elevated temperatures.

This study aims to investigate the effect of substrate temperature on the structural, optical, and photocatalytic properties of titanium dioxide (TiO₂) thin films deposited using the Radio Frequency (RF) magnetron sputtering technique. The optical properties were analyzed using Ultraviolet–Visible-Near Infrared (UV–VIS-NIR) spectrophotometry, and the energy band gap values were determined using the first derivative method. The energy band gap values were found to be 3.70 eV, 3.69 eV, and 3.69 eV for substrate temperatures of room temperature, 100 °C, and 200 °C, indicating a minimal effect of temperature on the band gap. Structural characterization using X-ray diffraction (XRD) revealed that substrate temperature significantly affects phase formation. Notably, a diffraction peak at 25.3°, corresponding to the (101) plane of the anatase phase, was observed only in the film grown at 200 °C. This observation is supported by Scanning Electron Microscopy (SEM) images, which confirm an improved crystal structure at this temperature. The photocatalytic efficiency of the films was assessed through the degradation of organic pollutants under UVA and UVC illumination. The film grown at 200 °C exhibited the highest photocatalytic performance, with a degradation efficiency of 96.15% after 4 h of UVC irradiation. This enhanced performance is attributed to the formation of the anatase phase and improved crystal structure. In light of these findings, this study provides important insights into the optimization of TiO₂ thin films for photocatalytic applications, particularly in environmental remediation and sustainable water treatment technologies. Future work could further enhance photocatalytic efficiency by employing doping strategies or heterojunction designs.

The heat and mass balance equations for diffusion and chemical reactions in a catalyst pellet are resolved for reactions adhering to a standard class of Langmuir–Hinshelwood and general-order kinetics. An explicit new algebraic expression for the effectiveness factor concerning the kinetic, adsorption, and transport characteristics in isothermal/non-isothermal conditions is reported using HFM and AGM methods. This equation may be used directly in fixed-bed reactor computations to account for the effects of adsorption and intraparticle dynamics. The advantage of HFM and AGM starts from their powerful approach for handling nonlinearities and complex boundary conditions, making them preferred for steady-state analysis in physical reaction systems. The results validate that both methods are superior, mainly when accuracy and computational efficiency are critical.

The present study aims the investigation of modifying bentonites in the elimination of both cationic and anionic dyes; Methylene blue and Congo red were chosen as models for each kind of dyes. Comprehensive characterization through FTIR, XRD, BET, SEM, and pH_PZC demonstrated the suitability of bentonites in the removal of dyes owing to theirs remarkable morphology, and texture. Several parameters that effect adsorption process of dyes were investigated, to establish the behavior and the removal mechanism such as: effect of modification of bentonite (purification, activation, and organophilization), effect of pH (2–12), and effect of temperature (10–40 °C). For both dyes, MB and CR adsorption kinetics are best described by the pseudo-second-order model, and Langmuir model for the isothermal study. pH parameter affects both dyes. MB Adsorption process is favorable in basic medium. CR adsorption process is favorable in acidic mediums for PBent, ABent and favorable in basic medium for OBent. MB/PBent, CR/ABent, and CR/OBent adsorption processes were found to be spontaneous and exothermic in nature owing to the negative values of the thermodynamic parameters. For MB/ABent, MB/OBent, and CR/PBent adsorption processes were found to be spontaneous and endothermic because the values of the thermodynamic parameters were found to be positive. The bentonites have achieved maximum MB adsorption capacities of 345.8, 152.6, and 347.2 mg/g for PBent, ABent, and OBent, respectively and CR adsorption capacities of 315.2, 4.96, and 205.85 mg/g for PBent, ABent, and OBent, respectively. From the obtained results, it can be said that all prepared bentonites are a very promising adsorbents of both cationic and anionic dyes and can be used successfully in the industrial of textile to remediate their wastewater.

NiIn intermetallic compounds are constructed over V₂CT_x MXene for the selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL). Ni₄In/V₂CT_x demonstrated a conversion rate of 93.6% for CAL, with a high selectivity of 77.4% for COL. The COL yield of Ni₄In/V₂CT_x is much greater than that of Ni₄In, Ni/V₂CT_x, and Ni₄In/Al₂O₃. Moreover, the V₂CT_x support is the key to the formation of NiIn intermetallic compounds, which effectively inhibit the oxidation of metallic Ni. NiIn metal particles are uniformly distributed on the surface of V₂CT_x, increasing the metal‒support interaction. Electron-deficient metallic Ni and In inhibit the hydrogenation of the C=C bond. Furthermore, the introduction of In provides more abundant and stronger Lewis acid sites, facilitating the adsorption of C=O bonds and thereby enhancing the selectivity for COL.