Hydrogen (H2) is a prospective zero-carbon, high-energy-density fuel to generate power and clean energy instead of using fossil fuels. Ammonia (NH3) is a promising H2 (17.7%) carrier which can easily...
Understanding the mechanism of methane activation and coupling of its derivatives catalyzed by metal carbides is critical to efficiently converting methane to value-added products via a direct conversion route. In the present work, we report a systematic density functional theory-based computational study of methane conversion on the W-terminated α-WC(0001) and W−C exposed α-WC(112̅ 0) surfaces. Our results indicate that methane dissociates by sequentially breaking its C−H bonds, resulting in the (CH) ads moieties on W-terminated α-WC(0001). Dimerization of (CH) ads through C−C coupling is facile, leading to (C 2 H 2 ) ads . In contrast, the stepped W sites on the α-WC(112̅ 0) surface promote C−H bond activation, and the C sites on the surface bind the dissociation intermediates and result in (C 2 H 2 ) ads through C−C coupling. Meanwhile, such (C 2 H 2 ) ads on α-WC(112̅ 0) is thermodynamically more favorable to dehydrogenate to the C−C ensembles, eventually forming atomic carbon deposits on the surface. The very different reactivities of the two WC surfaces toward C−H breaking and C−C coupling predict a varying distribution of products sensitive to the local structure of the catalysts, thereby the operating reaction condition.
The catalytic conversion of greenhouse gases, such as N2O, is a promising way to mitigate global warming. In this work, density functional theory (DFT) studies were performed to study N2O reduction by CO over single-atom catalysts (SACs) and compare the performance of noble (Au/C2N) and non-noble (Cu/C2N) SACs. The computational results indicated that catalytic N2O reduction on both catalysts occurs via two mechanisms: (I) the N2O adsorption mechanism—starting from the adsorption on the catalysts, N2O decomposes to a N2 molecule and O-M/C2N intermediate, and then CO reacts with O atom on the O-M/C2N intermediate to form CO2; and (II) the CO adsorption mechanism—CO and N2O are adsorbed on the catalyst successively, and then a synergistic reaction occurs to produce N2 and CO2 directly. The computational results show that mechanism I exhibits an obvious superiority over mechanism II for both catalysts due to the lower activation enthalpy. The activation enthalpies of the rate-determining step in mechanism I are 1.10 and 1.26 eV on Au/C2N and Cu/C2N, respectively. These results imply that Cu/C2N, an abundant-earth SAC, can be as active as expensive Au/C2N. Herein, our research provides a theoretical foundation for the catalytic reduction of N2O and broadens the application of non-noble-metal SACs.
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