The capability to activate methane at mild temperature and facilitate all elementary reactions on the catalyst surface is a defining characteristic of an efficient catalyst especially for the direct conversion of methane to ethylene. In this work, theoretical calculations are performed to explore such catalytic characteristic of an IrO 2 (110) surface. The energetics and mechanism for methane dehydrogenation reactions, as well as C-C coupling reactions on the IrO 2 (110) surface, are investigated by using van der Waals-corrected density functional theory calculations. The results indicate that a non-local interaction significantly increases the binding energy of a CH 4 molecule with an IrO 2 (110) surface by 0.35 eV. Such an interaction facilitates a molecular-mediated mechanism for the first C-H bond cleavage with a low kinetic barrier of 0.3 eV which is likely to occur under mild temperature conditions. Among the dehydrogenation reactions of methane, CH 2 dissociation into CH has the highest activation energy of 1.19 eV, making CH 2 the most significant monomeric building block on the IrO 2 (110) surface. Based on the DFT calculations, the formation of ethylene could be feasible on the IrO 2 (110) surface via selective CH 4 dehydrogenation reactions to CH 2 and a barrierless self-coupling reaction of CH 2 species. The results provide an initial basis for understanding and designing an efficient catalyst for the direct conversion of methane to ethylene under mild temperature conditions.

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Catalytic conversion of methane to value-added chemicals is a promising application for gas versatility. In this work, we have investigated the methane oxidation over oxygen-rich IrO2 (110) surface by DFT calculations, as IrO2 is reported to be an effective catalyst for activating the C–H bond of methane. Compared to the methane reaction on the surface of stoichiometric IrO2 (110), the reaction barrier for each step of forming formaldehyde on the oxygen-rich IrO2 (110) is small. The calculations show that formaldehyde formation is the most favorable route in methane oxidation, but this process is limited by the high desorption energy of formaldehyde. To modify the reactivity of IrO2 (110), we conducted a study of the influence of an external electric field on the methane conversion reaction. The calculations show that the effects of external electric field on methane dehydrogenation and C–O coupling reactions are not so apparent. However, it is found that the desorption energy of the adsorbates can be regulated by applying an external electric field. Our study indicates that the use of an external electric field is crucial in regulating the catalytic reaction, and especially the application of a positive electric field promotes the oxidation of methane to formaldehyde over oxygen-rich IrO2 (110) surface.

Ethanol steam reforming (ESR) is one of the potential processes to convert ethanol into valuable products. Hydrogen produced from ESR is considered as green energy for the future and can be an excellent alternative to fossil fuels with the aim of mitigating the greenhouse gas effect. The ESR process has been well studied, using transition metals as catalysts coupled with both acidic and basic oxides as supports. Among various reported transition metals, Ni is an inexpensive material with activity comparable to that of noble metals, showing promising ethanol conversion and hydrogen yields. Additionally, different promoters and supports were utilized to enhance the hydrogen yield and the catalyst stability. This review summarizes and discusses the influences of the supports and promoters of Ni‐based catalysts on the ESR process.

The investigation by microkinetic simulations provide detailed reaction mechanisms about the NH 3 oxidation on the RuO 2 (110) surface. There are 41 elementary reactions involved in the microkinetic model in which all the thermodynamic and kinetic parameters are obtained from density functional theory (DFT) calculations, and the entropy effects of each reaction are considered in the simulation. The differences in reaction mechanisms between the batch type and the steady state were characterized in this study. The selectivities to the oxidation products, including N 2 , NO, and N 2 O, depend on the oxidation conditions. The simulated results show that the O 2 /NH 3 ratio, system temperature, and pressure are the controlling factors that could alter the results of the oxidation. The microkinetic modeling demonstrates how these parameters affect the NH 3 conversion and the selectivities. The simulations showed that N 2 and NO could be a primary product under different oxidizing conditions; however, N 2 O could only be a minor product because of the nature of its formation mechanism. The highest N 2 O selectivity obtained in the simulations is 30%.

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