A cobalt rhenium catalyst active for ammonia synthesis at 400 °C and ambient pressure was studied using in situ XAS to elucidate the reducibility and local environment of the two metals during reaction conditions. The ammonia reactivity is greatly affected by the gas mixture used in the pre-treatment step. Following H2/Ar pre-treatment, a subsequent 20 min induction period is also observed before ammonia production occurs whereas ammonia production commences immediately following comparable H2/N2 pre-treatment. In situ XAS at the Co K-edge and Re LIII-edge show that cobalt initiates reduction, undergoing reduction between 225 and 300 °C, whereas reduction of rhenium starts at 300 °C. The reduction of rhenium is near complete below 400 °C, as also confirmed by H2-TPR measurements. A synergistic co-metal effect is observed for the cobalt rhenium system, as complete reduction of both cobalt and rhenium independently requires higher temperatures. The phases present in the cobalt rhenium catalyst during ammonia production following both pre-treatments are largely bimetallic Co-Re phases, and also monometallic Co and Re phases. The presence of nitrogen during the reduction step strongly promotes mixing of the two metals, and the bimetallic Co-Re phase is believed to be a pre-requisite for activity.

中文翻译：

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氨合成钴R催化剂的原位XAS研究。

使用原位XAS研究了在400°C和环境压力下对氨合成具有活性的钴rh催化剂，以阐明两种金属在反应条件下的还原性和局部环境。预处理步骤中使用的气体混合物会极大地影响氨的反应性。在H2 / Ar预处理之后，在产生氨之前还观察到随后的20分钟诱导期，而在类似的H2 / N2预处理之后立即开始氨生产。Co K边缘和Re LIII边缘的原位XAS显示钴开始还原，在225至300°C之间发生还原，而reduction的还原始于300°C。H2-TPR测量也证实，below的还原在400°C以下几乎完全完成。由于钴和system的完全还原独立地需要更高的温度，因此对于钴rh体系观察到了协同的共金属效应。在两种预处理之后的氨生产过程中，钴rh催化剂中存在的相主要是双金属Co-Re相，也包括单金属Co和Re相。在还原步骤中氮的存在强烈促进了两种金属的混合，并且双金属Co-Re相被认为是活性的先决条件。