Reaction Kinetics, Mechanisms and Catalysis最新文献

The catalytic conversion of CO(_2) into methane via the Sabatier reaction offers a promising route for carbon utilization and renewable energy storage, producing grid-compatible CH(_4) from CO(_2) and H(_2). Yet performance depends strongly on catalyst design, synthesis, and operating conditions, which remain inconsistently reported. This review systematically compares formulations and process parameters to identify conditions enabling high CO(_2) conversion and CH(_4) selectivity. Ru catalysts deliver superior low-temperature activity (300–400 (^{circ })C), while Ni remains cost-effective and robust at higher temperatures. Metal loading shows an optimum, beyond which larger crystallites and weaker metal–support interactions reduce performance. Supports and promoters critically tune basicity, reducibility, and vacancy density: CeO(_2) and CeZrO(_2) outperform Al(_2)O(_3), and rare-earth (La, Ce) and transition-metal (Mn, Co) promoters enhance CO(_2) adsorption and H(_2) activation. Synthesis routes such as sol–gel, plasma-assisted, and ammonia-evaporation methods strengthen dispersion and metal–support synergy, while nanostructured morphologies improve defect chemistry and active-site accessibility. Operating conditions are equally important. Optimal performance arises from moderate GHSV to balance throughput and contact time, a H(_2)/CO(_2) ratio near 4:1, and elevated pressures. Photothermal and photo-assisted strategies further lower activation barriers, particularly for Ru catalysts. Overall, effective CO(_2) methanation integrates defect-rich supports, optimized promoters, nanostructured synthesis, and carefully tuned operating conditions, with light-assisted approaches offering added potential. Future progress requires standardized testing and scale-up under dynamic operation to translate laboratory findings into viable Power-to-Gas systems.

The present study examines the effect of multilayer graphene (MLG) addition on the characteristics of Al-Bi₂O₃ nanothermite. Al-Bi₂O₃-MLG nanothermites with various MLG weight percentages (wt%) were synthesized by the physical mixing method. X-ray diffraction (XRD) confirmed the crystalline phases. Field emission scanning electron microscopy (FESEM) revealed agglomeration in the nanoparticles and the attachment of Al and Bi₂O₃ nanoparticles onto the MLG sheets in the nanothermites. Structural stability of MLG sheets present in synthesized samples is observed by the Raman spectroscopy. Differential scanning calorimetry (DSC) revealed that the Al-Bi₂O₃-MLG (2 wt%) nanothermite displayed the maximum energy release of 200 J/g among the synthesized nanothermites. Reaction kinetic analysis performed using the Popescu methods indicated that the reaction of Al-Bi₂O₃-MLG (2 wt%) nanothermite follows a fractional-order model. The mean activation energy, calculated using the Popescu method, was 169.8 ± 105.7 kJ/mol. Furthermore, thrust generation testing demonstrated that this nanothermite achieved a specific impulse of 60.5 s, representing an approximately 1.37-times enhancement over the Al-Bi₂O₃ nanothermite.

The catalytic degradation of methyl orange (MO) through peroxymonosulfate (PMS) activation was investigated using xCuZnO nanoparticles (x = 10, 30, and 50 wt%), synthesized via the sol–gel method and calcined at 500 °C. The prepared and calcined samples were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption, Raman spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX), X-ray photoelectron spectroscopy (XPS), and UV–Vis diffuse reflectance spectroscopy. The characterization results evidenced the coexistence of ZnO and CuO crystalline phases, along with a slight contraction of ZnO lattice upon increasing copper loading. All catalysts exhibited notable activity for MO degradation, with PMS addition, enhancing significantly the degradation rate from 45 to 90% within just 2 min while maintaining appreciable stability over 30 to 60 min. Mechanistic investigations revealed that superoxide radicals (O₂•⁻) were the primary reactive species responsible in MO degradation, along with photogenerated holes (h⁺) and electrons (e⁻), which also contributed to the overall photodegradation process. These findings highlight the potential of CuZnO/PMS system as an efficient alternative for industrial effluent treatment.

This research outlines the successful synthesis of a new and novel ternary heterojunction photocatalyst, CaFe₂O₄/ZnSe/TiO₂ for efficient degradation of dye under visible light irradiation. The study also provides insights into the morphology, structure, chemical composition of the composite and the mechanistic understanding behind the efficient photocatalytic activity. Results of scavenger experiments reveal hydroxyl radicals, superoxide radicals, and holes are the main reactive species involved in the degradation process. The hydrophilic nature of composite complimented in degradation of dye. Moreover, the composite showed outstanding stability and reusability throughout seven cycles. Germination studies using Cicer arietinum demonstrated the non-toxicity of the treated water, making it suitable for horticulture use. Therefore, the synthesized composite has potential use in environmental cleanup and wastewater management.

Graphical abstract

This research is dedicated to the preparation of activated carbon using olive stones (OSAC) and evaluates its performance in removing Cu²⁺ and Zn²⁺ ions from water, compared to two commercial carbons: powdered activated carbon (PAC) and granular activated carbon (GAC). OSAC exhibited the largest BET surface area (1299 m² g⁻¹), significant micropore volume (0.432 cm³ g⁻¹), and an abundance of oxygen-bonded functional groups. Adsorption kinetics were best represented by the pseudo-second-order model. The stirring speed, the pH of the solution, and the dose of adsorbent had a significant influence on the adsorption efficiency of Cu²⁺ and Zn²⁺ ions. Equilibrium isotherms fitted the Langmuir model, showing high maximum adsorption capacities for OSAC, as 50.29 mg g⁻¹ for Cu²⁺ and 43.72 mg g⁻¹ for Zn²⁺ at 20 °C, exceeding those obtained for PAC (39.48 mg g⁻¹ and 37.16 mg g⁻¹) and GAC (33.88 mg g⁻¹ and 28.13 mg g⁻¹) for Cu²⁺ and Zn²⁺. Thermodynamic data revealed that the adsorption mechanism is spontaneous and endothermic (ΔG° < 0, ΔH° > 0) governed by chemisorption in addition to physisorption. Collectively, these results establish OSAC, with enhanced surface properties, as a highly effective adsorbent. This provides an eco-friendly approach for the removal of heavy metals from wastewater, surpassing commercial activated carbons use.

This study focuses on the composition characteristics of coal tar, which is rich in aromatic hydrocarbons, and employs long-chain olefins as alkylating agents for directional modification of molecular groups. Gas chromatography–mass spectrometry was used as the primary analytical technique. The optimal process conditions for the alkylation reaction were investigated. Experiments were conducted on the alkylation of light fractions to analyze the component migration law during the alkylation of coal tar fractions, as well as on the alkylation of hydrogenated heavy fractions to examine the effect of hydrogenation pretreatment on the alkylation reaction. Finally, a preliminary performance evaluation of the products from each fraction was carried out. The results indicate that the optimal process conditions for the alkylation reaction are as follows: using AlCl₃ as the catalyst, a reaction temperature of 100 °C, and a reaction time of 3 h. The main substances undergoing alkylation in each coal tar fraction were identified as monocyclic aromatics containing hydroxyl groups and a small amount of bicyclic aromatics. Meanwhile, hydrogenation pretreatment was found to inhibit the alkylation reaction, primarily because the hydrogenation process removes hydroxyl groups from the aromatic rings, reducing the reactivity of the substrates, and because compounds such as tetralin generated during hydrogenation promote hydrogen transfer, leading to the saturation of olefins. The performance evaluation results show that key indicators, such as the viscosity of the products from each fraction, were significantly improved, demonstrating promising potential for industrial application.

A highly effective and recyclable heterogeneous catalyst, Ni-doped MXene, was developed for the synthesis of N-arylbenzamides from arene halides with arene amines, employing Co₂(CO)₈ as a solid CO surrogate. MXene, a novel two-dimensional nanomaterial, offers a high surface area and numerous active sites, making it an excellent support for nickel dispersion. Utilizing Co₂(CO)₈ as an inexpensive, less hazardous, and low-melting alternative to gaseous CO represents a significant advancement over conventional methodologies. The catalyst exhibited remarkable yields across a broad substrate scope, including both electron-withdrawing and electron-donating groups. The influence of solvent, catalyst loading, and reaction parameters was systematically studied to optimize the reaction conditions. Comprehensive characterization of both fresh and recycled Ni-MXene catalysts was performed using XRD, XPS, BET, and ICP-OES techniques. Furthermore, the catalyst is readily recoverable and can be reused for up to five cycles without a significant loss of reactivity. These analyses confirmed a uniform dispersion of nickel across the MXene surface, with the formation of well-defined Ni nanoclusters averaging approximately 4 nm in diameter.

Graphical abstract

In this article, we have theoretically studied the L-Alanine decarboxylation reaction catalyzed by pyridoxal 5′-phosphate-based aldimine (denoted as PLP) at M06-2X-D3/6-311G(d,p)/IEFPCM level of theory. The reaction went through amine acetal formation, decarboxylation and catalyst regeneration procedures, and the rate-determining step is decarboxylation reaction with 28.2 kcal/mol activation Gibbs free energy barrier. The role of protonated pyridine (PyH⁺) moiety of PLP was investigated by theoretically studying isoelectronic species (IES)-catalyzed reaction, PLP is more catalytic active than IES because PLP can lower the activation free energy barrier by means of increasing aromaticity of PyH⁺ moiety but the phenyl moiety of IES cannot, indicating the PyH⁺ moiety of PLP cannot be replaced arbitrarily.

Here, a solvothermal method was utilized to prepare Co₃O₄ with diverse values of adsorbed oxygen/lattice oxygen (O_ads/O_latt) and low-temperature reducibility by modulating H₂O/CH₃CH₂OH solvent ratio. As the ethanol content increases, both O_ads/O_latt ratio and redox ability exhibit a marked progressive promotion owing to the rapid formation of Co(OH)₂ precipitation inhibited by ethanol. Compared to O_ads/O_latt ratio, low-temperature redox ability exhibits a stronger correlation with propane reaction rate at 210 °C (R² = 0.97 vs 0.69), establishing it as the primary factor governing the reaction kinetics of low-temperature propane oxidation. Additionally, in-situ DRIFTS demonstrates that accelerated redox cycle of Co³⁺/Co²⁺ drives the reaction pathway for propane oxidation: CH₃CH₂CH₃ → CH₂CHCH₃ → CH₂CHCOOH → CO₃²⁻ → CO₂. As a result, Co₃O₄-40 (H₂O/CH₃CH₂OH solvent ratio = 0/40) displays a prominent excellent and competitive propane oxidation activity (R_210°C = 3.42 μmol g_cat⁻¹ s⁻¹).

Nanosized zeolite Y with high Si/Al ratio was successfully synthesized from coal gangue(denoted as CG) using an ultrasonic assisted two-step ageing method. The raw CG, its intermediates and as-synthesized zeolite samples were characterized by XRD, XRF, SEM, ICP-AES, N₂ adsorption–desorption, NH₃-TPD. The extraction ratios of silica and alumina from CG reached 78.9% and 72.2%. The homogeneous initial gel was obtained by ultrasonic-assisted aging. The acid leaching residue (denoted as ALR) from CG was added to the aged initial gel, and after ageing, the FAU crystals with Si/Al ratio of 2.45 and size of 46 nm were hydrothermally synthesized at 60 °C. The results of TIPB (1.3.5-triisopropylbenzene) catalytic cracking tests showed that the as-synthesized zeolite Y had higher activity than the commercial catalyst HSZ-320 NAA. The above results suggest the economic route for synthesizing nanosized zeolite Y from CG instead of expensive raw materials.