Theoretical insight into methanol steam reforming on indium oxide with different coordination environments

Indium oxide (In₂O₃) has demonstrated to be an effective non-noble metal catalyst for methanol steam reforming reaction (MSR). However, the reaction mechanism of MSR and crucial structure-activity relations determining the catalytic performance of In₂O₃ are still not fully understood yet. Using density functional theory (DFT) calculation, we systematically investigate the MSR process over a high-index In₂O₃(211) and a favoured catalytic cycle of MSR is determined. The results show that In₂O₃(211) possesses excellent dehydrogenation and oxidizing ability, on which CH₃OH can readily adsorb on the In_4c site and be easily activated by the reactive lattice oxygens, resulting in a total oxidation into CO₂ rather than CO, while the H₂ formation through surface H–H coupling limits the overall MSR activity because of the strong H adsorption on the two-coordinated lattice O (O_2c). Our analyses show that the relatively inert three-coordinated lattice O (O_3c) could play an important catalytic role. To uncover the influence of the local coordination of surface In atoms and lattice O on the catalytic activity, we evaluate the activity trend of several types of In₂O₃ surfaces including (211), (111), and (100) by examining the rate-limiting, which reveals the following activity order: (211)>(111)>(100). These findings provide an in-depth understanding on the MSR reaction mechanism over In₂O₃ catalysts and some basic structure-activity relations at the atomic scale, could facilitate the rational design of In₂O₃-based catalysts for MSR by controlling the local coordination environment of surface active sites.