Hydrogen spillover enabled active Cu sites for methanol synthesis from CO2 hydrogenation over Pd doped CuZn catalysts
Hydrogen spillover enabled active Cu sites for methanol synthesis from CO2 hydrogenation over Pd doped CuZn catalysts
复制标题
氢气溢出使活性铜位点能够在 Pd 掺杂 CuZn 催化剂上从 CO2 加氢合成甲醇
DOI：
10.1016/j.jcat.2017.12.029
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发表时间：
2018-03-01
影响因子：
7.3
通讯作者：
Tsang, Shik Chi Edman
中科院分区：
文献类型：
--
作者：
Hu, Bing;Yin, Yazhi;Tsang, Shik Chi Edman
采用Pd对Cu-ZnO催化剂进行表面改性是通过氢溢出机制提高其CO2加氢制甲醇活性的有效途径。然而，目前还缺乏对氢溢出效应的定量分析，Pd修饰后活性中心的性质也不清楚。本论文采用多元醇还原法制备了一系列Pd负载量可调的Pd掺杂Cu-ZnO催化剂（Pd-CZ-x），深入研究了Pd的助催化作用。随着Pd/Cu摩尔比（x）从0增加到0.04，甲醇空时产率（STY）与Pd负载量之间呈现火山形关系。与未掺杂的Cu-ZnO相比，1%的Pd掺杂可以使甲醇STY增加2.5倍，并且在543 K下甲醇周转频率（TOF）增加3.5倍。动力学研究表明，甲醇合成所需的活化能大大降低，从59 kJ mol（-1）的Cu-ZnO上的Pd-CZ-0.01上的31 kJ mol（-1）。在火山形关系的背后是Pd的氢溢出效应和由Pd阻挡引起的表面Cu面积减少之间的平衡。化学吸附给出了一个重要类型的激活铜网站的定量分析，使氢溢出（小熊）。重要的是，它被发现，甲醇STY与Cuhs的表面积线性相关，这表明在ZnO的辅助下活化的Cu位是真实的活性位的CO2加氢合成甲醇。(C)2018爱思唯尔公司All rights reserved.
Surface modification with Pd is an effective way for improved activity in CO2 hydrogenation to methanol over commercial Cu-ZnO catalysts via a so-called hydrogen spillover mechanism. However, there still lacks a quantitative analysis of hydrogen spillover effect and the nature of active sites after Pd modification remains unclear. In this work, we prepared a series of Pd-doped Cu-ZnO catalysts (Pd-CZ-x) with tunable Pd loading by using a facile polyol reduction method for a deep study of the promotion effect of Pd. With the increase of Pd/Cu molar ratio (x) from 0 to 0.04, there emerges a volcano-shaped relationship between methanol space time yield (STY) and Pd loading. 1% Pd doping can increase the methanol STY by 2.5 times and the methanol turnover frequency (TOF) by 3.5 times at 543 K, when compared to undoped Cu-ZnO. Kinetic studies show the activation energy required for methanol synthesis is greatly reduced from 59 kJ morl over Cu-ZnO to 31 kJ mol(-1) over Pd-CZ-0.01. Behind the volcano-shaped relationship is a balance between the hydrogen spillover effect of Pd and the reduced surface Cu area caused by Pd blocking. Chemisorption gives a quantitative analysis of an important type of activated Cu sites enabled by hydrogen spillover (Cubs). Importantly, it is found that the methanol STY correlates linearly with Cuhs surface area, suggesting that the activated Cu sites with the assistance of ZnO are real active sites for methanol synthesis from CO2 hydrogenation. (C) 2018 Elsevier Inc. All rights reserved.