Cubic α-phase molybdenum carbides (α-MoC_1–x) exhibit great potential in hydrogen production at low temperatures due to their excellent activity in water dissociation. However, the design strategies of α-MoC_1–x are severely restricted by the harsh synthesis conditions, which involve multistep ammonification and carburization or the utilization of a significant amount of noble metals. Herein, high-purity α-MoC_1–x synthesis in a one-step carburization process was achieved with the assistance of a trace amount of Rh (0.02%). The structural evolution of Mo species during phase transition was monitored via qualitative and quantitative analysis by in situ X-ray diffraction (XRD) and in situ X-ray absorption spectroscopy (XAS), respectively. Environmental transmission electron microscopy (ETEM) was used to follow the visual changes. We reveal that the reduction of monoclinic MoO₃ to cubic oxygen-deficient Mo oxide (MoO_x) at low temperatures owing to the promoted H₂ activation on Rh sites is vital to the following carbon atom insertion and transformation to α-MoC_1–x, making the carburization follow the topological route. The systematic analysis of the relationship between the reduction behavior and the structural evolution supplies a feasible strategy for the α-MoC_1–x synthesis, and in situ characterizations shed light on controlling the phase transformation during carburization.

中文翻译：

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立方 α-MoC1–x 催化剂简易合成过程中结构演化的原位研究

立方 α 相碳化钼 (α-MoC _{1– x} ) 由于其优异的水解离活性，在低温下具有巨大的制氢潜力。然而，α-MoC _{1– x}的设计策略受到苛刻的合成条件的严重限制，这些条件涉及多步氨化和渗碳或使用大量贵金属。在此，在微量 Rh (0.02%) 的帮助下，在一步渗碳过程中实现了高纯度 α-MoC _{1 - x合成。}通过原位X 射线衍射 (XRD) 和原位X射线吸收光谱（XAS），分别。环境透射电子显微镜 (ETEM) 用于跟踪视觉变化。我们发现，由于促进了 Rh 位点上的 H _{2活化，单斜晶系 MoO 3}在低温下还原为立方缺氧 Mo 氧化物 (MoO _x )对于随后的碳原子插入和转化为 α-MoC _{1– x}至关重要，使渗碳遵循拓扑路线。还原行为与结构演化之间关系的系统分析为 α-MoC _{1- x}合成提供了可行的策略，并且原位表征揭示了控制渗碳过程中的相变。