Reaction Kinetics, Mechanisms and Catalysis最新文献

Nanoporous Co_100-xNi_x (x = 1, 5, 10 and 15) solid solutions were synthesized using the chemical coprecipitation followed by hydrogen reduction method and applied as catalysts for the efficient hydrogen generation from NaBH₄ hydrolysis. The obtained catalysts are composed of hcp- and fcc-(Co,Ni) solid solutions phases, and exhibit the special three-dimensional nanoporous structure. With increasing the Ni content, the hydrogen generation rate (HGR) of NaBH₄ hydrolysis catalyzed by Co_100-xNi_x solid solutions decreased slightly, whereas the cycling stability of the catalyst can be improved. The HGR remains as much as 73% of the initial value after five times of catalysis for Co₈₅Ni₁₅. This work contributes to the development of advanced non-noble metal-based catalysts for efficient and long-term hydrogen generation from NaBH₄ hydrolysis.

In this work, we introduced a simple approach to boost the photocatalytic activity of MoS₂ by introducing transition metal (W) doping. The W-MoS₂ (10 mg) exhibited a substantial enhancement in photocatalytic activity for H₂ production, achieving an impressive rate of approximately 925 µmol g⁻¹ after 6 h, which is 1.5-fold higher than bare MoS₂. The highest H₂ production activity of 1740 µmol g⁻¹ after 6 h was obtained for 50 mg W-MoS₂ photocatalyst. The observed increase in activity can be ascribed to the formation of a Schottky barrier at the heterojunction interface, along with advantageous properties of improved active sites resulting from tungsten doping into MoS₂. Furthermore, the enhanced activity of W-MoS₂ may be attributed to the promotion of catalytic kinetics by tungsten and molybdenum sites, exhibiting commendable activity for water dissociation and higher efficiency in H⁺ adsorption. These factors contribute significantly to the overall improved performance of the W-MoS₂ photocatalyst. Further, platinum (Pt) was also used as cocatalyst and enhanced photocatalytic activity of 2145 µmol g⁻¹ after 6 h was observed for W-MoS₂ + 5 wt% Pt.

The combustion characteristics of coconut shell, coal water slurry, and biomass were studied by combustion thermogravimetry at different heating rates. The DTG curves of all samples exhibit three distinct peaks. The comprehensive combustion characteristic index (S_N) of coconut shell and biomass was higher, and the ignition point and burnout temperature were lower. At the same heating rate, the S_N of coal water slurry is the highest, the S_N of coconut shell, coal water slurry and biomass increased by 337%, 259%, and 429%. Based on the distributed Coats–Redfern integral method, the combustion kinetics of the samples was analyzed. The activation energy of low temperature combustion zone is higher than that in high temperature combustion zone. As the heating rate increases, the activation energy of the samples decreases slightly, but the overall trend remains similar. When n = 2, the fitting curve has a good linear relationship, and the correlation coefficient R² is all above 0.99.

This research was aimed at developing a base catalyst from the ash of moringa leaves that has high-performance biodiesel production. The moringa leaves were washed, dried, and then pounded into powder ash. Three temperature variations were used to calcinate the moringa leaves ash: 700 °C (MA-700), 800 °C (MA-800), and 900 °C (MA-900). Low-grade Bali Malapari oil (LMO) was degummed by heating and then treated with an 85% H₃PO₄ solution, which was referred to as DMO. The DMO oil was esterified using methanol and concentrated H₂SO₄ (EDMO). Because MA-900 contained the highest concentration of CaO, it was chosen to serve as the catalyst. The MA-900 was used in the production of biodiesel under the following conditions: temperature of reaction (55, 60, and 65 °C); oil-to-methanol mole ratio (1:3, 1:6, and 1:9); catalyst-to-oil weight ratio variables (3 wt%, 6 wt%, and 9 wt%); and reaction times (60, 90, 120, and 150 min). The biodiesel products were analyzed using FTIR and GC–MS. The best-performing conditions were conducted for catalyst usability test for three-run cycles. The highest biodiesel yield was achieved using a 1:6 oil:methanol mole ratio and a 3% catalyst/oil weight ratio at 60 °C reaction temperature, which lasted for 120 min and resulted in a biodiesel yield of 87.2wt% with 100% selectivity. The usability test performed on the MA-900 catalyst resulted in a biodiesel yield that was 87.2%, 86.4%, and 84.8% after three-run cycles.

The multifunctional groups of 5-hydroxymethylfurfural (5-HMF) make it could extend carbon chain by different C–C coupling reactions and extensively applied in the bio-jet fuel synthesis. Herein, one-pot reaction of lignocellulose derived chemicals with 5-HMF was studied by experimental and density functional theory (DFT) methods. The kinetic models of products were established and the apparent activation energies of the products by C–C coupling reaction of phenol, anisole, guaiacol, cyclohexanone and acetone with 5-HMF on Hβ were 95.3 kJ/mol, 104.8 kJ/mol, 90.4 kJ/mol, 90.0 kJ/mol and 112.2 kJ/mol, indicating these reactions centering on 5-HMF competitive intensively. Then the effects of the catalysis were analyzed by applying commercial catalysis to the mixed coupling reaction of 5-HMF. It was found that Brønsted acid is more favorable to alkylation reaction, and Lewis acid is more beneficial to aldol condensation reaction. By Fukui function, due to the nucleophilic index of cyclohexanone (2.74 eV) is higher than that (2.48 eV) of acetone, and the Mulliken electronegativity (3.43 eV) is weaker than that (3.55 eV) of acetone, cyclohexanone is more conducive than acetone to the aldol condensation reaction. This work provides data reference for product regulation in the bio-jet fuel synthesis.

The aim of this study was to deposit a Ni–La–Zr catalyst on a FeCrAl monolith by in situ growth of the catalyst on a metallic surface through immersion in a modified polymeric precursor solution. The prepared monolith was characterized by X-ray diffraction, atomic force microscopy, and scanning electron microscopy and was tested in a tri-reforming reaction of simulated biogas (CH₄/CO₂ = 3) for synthesis gas production. The monolithic catalyst presented better stability than the powdered catalyst under the 50-h test. In contrast, the powdered catalyst showed more pronounced deactivation, which was associated with higher carbon deposition. This study provides valuable information on a simple deposition method for Ni-based catalysts on FeCrAl monoliths for biogas tri-reforming reactions, which could have implications for biogas upgrading.

The current study aims to develop an error analysis for non-linear parabolic singularly perturbed reaction–diffusion problems using element-free Galerkin method. A robust numerical methodology is introduced based on combining the implicit Crank–Nicolson scheme for temporal derivatives and the element-free Galerkin (EFG) method for spatial derivatives. The moving least-squares (MLS) approximation has been employed to generate the shape functions. Essential boundary conditions have been enforced by the incorporation of the Lagrange multiplier method. Due to the presence of steep boundary layers in the solution of the considered problem, a piecewise-uniform layer-adapted Shishkin’s technique has been used to generate nodal points at the transition point. The stability and error analysis of the present method on a discrete (L^{2}-)norm is analyzed in an innovative theoretical framework. The (epsilon)-uniform convergency of the fully-discrete EFG method is shown to be (mathcal {O}(tau ^{2}+d_{s}^{m})), where (tau) and (d_{s}^{m}) are the time step size and size of the influence domain, respectively. The Lagrange multiplier method has been incorporated to deal with the implementation of essential boundary conditions. Lastly, a few numerical experiments are performed to validate the theoretical results and verify the computational consistency and robustness of the proposed scheme. The (L_{infty }) errors and the convergence rate have been presented.

The decomposition mechanism of H₂O₂ on X₁₂Y₁₂ (X = B, Al, Ga and Y = N, P) nanocages is studied by density functional theory (DFT) calculations. Generally, the decomposition of H₂O₂ proceeds through a direct dehydrogenation pathway. *H + *OH + *O is identified as the most thermodynamically stable intermediate. The unfavorable nature of peroxide bond scission directly pathway is attributed to the high energy barrier of *H separation from *OH + *O + *H, which favors the H₂O production. H₂O₂ is likely to dissociate on the Al₁₂N₁₂ via the direct dehydrogenation pathway, as the energy barrier of the rate-determining step is only 0.73 eV.

Co–xCaO/g-C₃N₄ catalysts were prepared using incipient wetness impregnation method and applied in isophthalonitrile hydrogenation to M-xylenedimethylamine. The characterization results and experimental data indicate that introduction of CaO crates large number of basic sites and leads to electron rich Co, hence inhibits the side reaction and improves the selectivity to M-xylenedimethylamine. 10Co–2CaO/g-C₃N₄ gives the best catalytic performance of 100% conversion of isophthalonitrile and 95% selectivity to M-xylenedimethylamine without any alkaline additives in the reacion system. This work is valuable for the design and preparation of hydrogenation catalysts with rich basic sites and provides a green process for nitrile compounds to amine.

A modified Friedman isoconversional method based on the weight-loss data was proposed to determine the kinetics models and parameters. Thermal pyrolysis kinetic characteristics of waste tire rubber (WTR) samples under nitrogen conditions was investigated by measuring the rate of mass loss as a function of time and temperature. The obtained thermal pyrolysis data was applied to analyze the kinetic parameters using the Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS) and modified Friedman isoconversional methods. The results showed that the modified Friedman isoconversional method was used to provide the most precise values of activation energy for WTR pyrolysis, which ranged from 130.5 to 177.6 kJ/mol with the conversion range of 0.1–0.9. It can avoid systematic errors in the FWO and KAS methods. These data were in good agreement with the values reported in the related previous studies. Therefore, the modified Friedman method provides an accurate and effective way to explain the pyrolysis parameters and equations of kinetics in WTR.