Ab initio derived reaction mechanism for the dry reforming of methane on Rh doped pyrochlore catalysts

C-H bond activation in light alkanes: a theoretical perspective

Alkanes are the major constituents of natural gas and crude oil, the feedstocks for the chemical industry. The efficient and selective activation of C-H bonds can convert abundant and low-cost hydrocarbon feedstocks into value-added products. Due to the increasing global demand for light alkenes and their corresponding polymers as well as synthesis gas and hydrogen production, C-H bond activation of light alkanes has attracted widespread attention. A theoretical understanding of C-H bond activation in light hydrocarbons via density functional theory (DFT) and microkinetic modeling provides a feasible approach to gain insight into the process and guidelines for designing more efficient catalysts to promote light alkane transformation. This review describes the recent progress in computational catalysis that has addressed the C-H bond activation of light alkanes. We start with direct and oxidative C-H bond activation of methane, with emphasis placed on kinetic and mechanistic insights obtained from DFT assisted microkinetic analysis into steam and dry reforming, and the partial oxidation dependence on metal/oxide surfaces and nanoparticle size. Direct and oxidative activation of the C-H bond of ethane and propane on various metal and oxide surfaces are subsequently reviewed, including the elucidation of active sites, intriguing mechanisms, microkinetic modeling, and electronic features of the ethane and propane conversion processes with a focus on suppressing the side reaction and coke formation. The main target of this review is to give fundamental insight into C-H bond activation of light alkanes, which can provide useful guidance for the optimization of catalysts in future research.

Process of CH4-CO2 reforming over Fe/SiC catalyst under microwave irradiation

In this work, the properties of the CH₄-CO₂ reforming reaction over the Fe/SiC catalyst during the whole process were studied under microwave irradiation and the reaction process was analyzed by mass spectrometry and Fourier transfer infrared spectrometry in real time. The effects of microwave power on the gas composition, conversion of reactants, and selectivity of products in the reaction were investigated. It was found that the microwave dry reforming reaction can be divided into a rapid reaction stage, slow reaction stage, and reaction equilibrium stage. The conversion of reactants and selectivity of products in the slow reaction stage were both higher than 95% under 90 W/g. In the long-term (~50 h) stability test, a combination of SEM, XRD, BET, and TG analyses found that the catalyst activity did not reduce significantly and the amount of carbon deposits (which was mainly C_γ) was negligible (~0.78 wt%). The results indicate that the cheap Fe-based catalyst has good catalytic activity and stability under microwave irradiation and hence has a promising application.

Dry Reforming of Methane on Carriers and Oxide Catalysts to Synthesis-Gas

The catalytic activity of carriers: θ‒Al2O3, γ‒Al2O3, 5A, 4A, 3A and 13X and the oxides of metals of variable valency ‒ NiO, La2O3, CuO, MoO3, MgO, V2O5, WO3, CoO, Cr2O3, ZnO, ZrO2, CeO2, Fe2O3, supported on the effective carrier γ‒Al2O3 by the method of capillary impregnation of the support with solutions of nitric salts of metals were investigated in the process of carbon dioxide conversion of methane (DRM). The optimal technological regimes for the process were: the reaction temperature -800 °C, the space velocity of the initial reactants ‒ 1500 h-1 with a methane to carbon dioxide ratio equal to 1. It was found that among the studied catalysts the highest activity is shown by the NiO/γ‒Al2O3 catalyst, where the yields of hydrogen and carbon monoxide reaches 45.4 and 42.4% by volume, respectively, when methane conversion is 89%. The XRF method showed that the content of alumina and nickel oxide after the reaction remained unchanged at 96.7 and 3.0%, respectively. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), small angle X-ray scattering (XRS) determined that nickel-containing NiO/γ‒Al2O3 catalyst form nickel nanoparticles (6.4‒10 and 50‒150 nm) and a uniform their distribution on the surface of the carrier takes place. These physical chemical characteristics have a positive effect on the activity of NiO/γ‒Al2O3 catalyst in the process of carbon dioxide conversion of methane to synthesis gas.

Monitoring the Reaction Mechanism in Model Biogas Reforming by In Situ Transient and Steady-State DRIFTS Measurements

In this work, the reforming of model biogas was investigated on a Rh/MgAl₂ O₄ catalyst. In situ transient and steady-state diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements were used to gain insight into the reaction mechanism involved in the activation of CH₄ and CO₂ . It was found that the reaction proceeds through of an initial pathway in which methane and CO₂ are both dissociated on Rh metallic sites and additionally a bifunctional mechanism in which methane is activated on Rh sites and CO₂ is activated on the basic sites of the support surface via a formate intermediate by H-assisted CO₂ decomposition. Moreover, this plausible mechanism is able to explain why the observed apparent activation energy of CO₂ is much lower than that of CH₄ . Our results suggest that CO₂ dissociation facilitates CH₄ activation, because the oxygen-adsorbed species formed in the decomposition of CO₂ are capable of reacting with the CH_x species derived from methane decomposition.