An In Situ XAS Study of the Cobalt Rhenium Catalyst for Ammonia Synthesis.
An In Situ XAS Study of the Cobalt Rhenium Catalyst for Ammonia Synthesis.
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用于氨合成的钴铼催化剂的原位 XAS 研究。
DOI：
10.1007/s11244-018-0892-7
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发表时间：
2018
影响因子：
3.6
通讯作者：
Mathisen K
中科院分区：
文献类型：
--
作者：
Mathisen K
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铼催化剂，以阐明两种金属在反应条件下的还原性和局部环境。氨的反应性很大程度上受预处理步骤中使用的气体混合物的影响。在 H2/Ar 预处理之后，在氨产生发生之前还观察到随后的 20 分钟诱导期，而氨生产在类似的 H2/N2 预处理之后立即开始。 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，而铼的还原在 300 °C 开始。 H2-TPR 测量也证实了铼在 400°C 以下的还原几乎完全。对于钴铼系统观察到协同共金属效应，因为钴和铼的完全还原独立地需要更高的温度。经过两种预处理后的氨生产过程中，钴铼催化剂中存在的相主要是双金属 Co-Re 相，以及单金属 Co 和 Re 相。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。
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/N2pre-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.