Pd/ZnO catalysts for direct CO2 hydrogenation to methanol
Pd/ZnO catalysts for direct CO2 hydrogenation to methanol
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DOI：
10.1016/j.jcat.2016.03.017
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发表时间：
2016-11-01
影响因子：
7.3
通讯作者：
Lalev, Georgi
中科院分区：
文献类型：
--
作者：
Bahruji, Hasliza;Bowker, Michael;Lalev, Georgi
二氧化碳直接氢化成甲醇对于提供一种固定二氧化碳的方法和一种以更高能量密度和更可运输的形式储存清洁产生的氢的方式至关重要。在这里，我们制备了两个系列的Pd/ZnO催化剂，都是通过固定化PVA保护的Pd胶体和Pd浸渍PdCl2来研究CO2直接加氢的结构和活性关系。不同制备方法的催化剂性能有很大差异，催化剂的Pd负载量和预还原量是影响甲醇收率的重要因素。甲醇产率高的关键因素是Pd-Zn合金的形成，无论是在反应过程中，还是通过高温预还原更好。合金的形成大大减少了逆水煤气变换反应产生的CO。溶胶-固定化法制备的催化剂对热处理相对稳定。相比之下，浸渍催化剂的热稳定性要差得多，这是因为催化剂表面存在残留的氯，这在溶胶固定化制备的情况下是不存在的。结果表明，在250℃和20bar的温度下，控制PdZn的粒度和表面结构对于获得高的甲醇选择性(60%，其余为CO)和转化率(11%)是非常重要的。溶胶固定化催化剂的选择性从平均直径3 nm时的60%下降到7 nm时的20%。(C)2016年提交人。由爱思唯尔公司出版。
The direct hydrogenation of CO2 into methanol is crucial for providing a means of CO2 fixation and a way to store cleanly produced hydrogen in a more energy-dense and transportable form. Here we have prepared two series of Pd/ZnO catalysts, both by immobilisation of PVA-protected Pd colloids and by Pd impregnation of PdCl2 to investigate structure activity relationships for direct CO2 hydrogenation. Very different performances were found for the different preparation methods, and the Pd loading and pre-reduction of the catalysts were shown to be important factors for optimising methanol yield. The crucial factor for high methanol yield is the formation of a Pd-Zn alloy, either during the reaction itself, or better by high temperature pre-reduction. The formation of the alloy greatly reduces CO production by the reverse water gas shift reaction. The catalysts prepared by sol-immobilisation were relatively stable to thermal treatment. In contrast, the impregnated catalysts were much less thermally stable, due to the presence of remnant chloride on the surface of the catalyst, which was absent for the case of sol immobilisation preparation. The results illustrate the importance of controlling the PdZn particle size and its surface structure for the catalysts to achieve high methanol selectivity (60%, the rest being CO) and conversion (11%) at 250 degrees C and 20 bar. Selectivity for sol-immobilised catalysts decreases from 60% at 3 nm average diameter, to 20% at 7 nm. (C) 2016 The Authors. Published by Elsevier Inc.