Highly activated K-doped Hägg-carbide/charcoal nanocatalyst at K/Fe = 0.075 showed the highest FTY value, the best hydrocarbon yield, and a good gasoline selectivity for the high-temperature Fischer–Tropsch reaction.
Catalytic decomposition of ammonia (NH 3 ) is a promising chemical reaction in energy and environmental applications. Density functional theory (DFT) calculations were performed to clarify the detailed catalytic mechanism of NH 3 decomposition on an Fe(100) surface. Specifically, the elementary steps of the mechanism were calculated for the general dehydrogenation pathway of NH 3 . The adsorption of two types of ammonia dimers (2NH 3 ), locally adsorbed NH 3 and hydrogen-bonded NH 3 , were then compared, revealing that locally adsorbed NH 3 is more stable than hydrogen-bonded NH 3 . By contrast, the dehydrogenation of dimeric NH 3 results in a high energy barrier. Moreover, the catalytic characteristics of NH 3 decomposition on a nitrogen (N)-covered Fe surface must be considered because the recombination of nitrogen (N 2 ) and desorption have an extremely high energy barrier. Our results indicate that the catalytic characteristics of the NH 3 decomposition reaction are altered by N coverage of the Fe surface. This study primarily focused on energetic and electronic analysis. Finally, we conclude that Fe is an alternative catalyst for the decomposition of NH 3 in CO x -free hydrogen production.
We report first-principles calculations of adsorption, dissociation, penetration, and diffusion for the complete nitridation mechanism of nitrogen molecules on a pure Fe surface (bcc, ferrite phase). The mechanism of the definite reaction path was calculated by dividing the process into four steps. We investigated various reaction paths for each step including the energy barrier based on the climb image nudged elastic band (CI-NEB) method, and the complete reaction pathway was computed as the minimum energy path (MEP). The adsorption characteristics of nitrogen (N) and molecular nitrogen (N2) indicate that nitrogen atoms and molecules are energetically favorable at the hollow sites on pure Fe(100) and (110). The dissociation of the nitrogen molecule (N2) was theoretically supported by electronic structure calculations. The penetration of nitrogen from the surface to the sub-surface has a large energy barrier compared with the other steps. The activation energy calculated for nitrogen diffusion in pure bcc Fe was in good agreement with the experimental results. Finally, we confirmed the rate-determining step for the full nitridation reaction pathway. This study provides fundamental insight into the nitridation mechanism for nitrogen molecules in pure bcc Fe.
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