CO Oxidation over Au/ZnO: Unprecedented Change of the Reaction Mechanism at Low Temperature Caused by a Different O2 Activation Process
CO Oxidation over Au/ZnO: Unprecedented Change of the Reaction Mechanism at Low Temperature Caused by a Different O2 Activation Process
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DOI：
10.1021/acscatal.9b02128
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发表时间：
2019-09-01
期刊：
影响因子：
12.9
通讯作者：
Haruta, Masatake
中科院分区：
文献类型：
--
作者：
Fujita, Takashi;Ishida, Tamao;Haruta, Masatake
共沉淀法制备的Au/ZnO对室温以下的CO低温氧化表现出极高的催化活性。制备过程中的还原气氛和反应前的空气热处理对催化活性有较大影响。H-2对Au（III）的还原不仅得到了更小的Au颗粒（Au/ZnO (H-2-xK)， H-2在x = 373-673 K下处理），而且得到了比在空气中煅烧（Au/ZnO (O-2 -xK)）更多的Au-0物质，从而获得了更好的活性。此外，在CO氧化之前，Au/ZnO （H-2-xK）在空气中热处理后，催化活性明显增强。动力学测量表明，Au/ZnO （H-2-xK）的活化能（E-a）在低于253 K时突然从26 kJ mol（-1）变为1.6 kJ mol(-1)，而Au/ZnO （O-2-xK）的活化能（E-a）保持不变，表明Au/ZnO （H-2-xK）的反应机理在253 K时发生了变化。紫外可见光谱分析表明ZnO存在较多的缺陷。电子顺磁共振结果表明，在空气中进行H-2还原和热处理可以增加ZnO氧空位或氧空位上形成的O-2自由基的数量。在程序升温解吸中，热处理后Au/ZnO （H-2-xK）的解吸峰温度低于热处理前Au/ZnO （H-2-xK）和Au/ZnO （O-2- xk）的解吸峰温度。这些结果表明，Au/ZnO （H-2-xK）的热处理产生了氧空位，O-2在界面周围被激活，活性氧很容易解吸。这些氧空位可能在较低温度下变得更有效，导致反应机理在253 K时发生变化。研究表明，周长界面对O-2活化的影响随温度的变化而变化，可以通过制备催化剂和热处理来控制。
Au/ZnO prepared by coprecipitation exhibited extremely high catalytic activity for low-temperature CO oxidation below room temperature. The catalytic activity was influenced by the reduction atmosphere in the preparation and the heat treatment in air before the reaction. Reduction of Au(III )by H-2 not only gave smaller Au particles (Au/ZnO (H-2-xK), H-2 treatment at x = 373-673 K) but also a larger amount of Au-0 species than did calcination in air (Au/ZnO (O-2 -xK)), resulting in better activity. In addition, the catalytic activity of Au/ZnO (H-2-xK) was markedly enhanced by heat treatment in air prior to the CO oxidation. Kinetic measurements revealed that the activation energy (E-a) of Au/ZnO (H-2-xK) suddenly changed from 26 to 1.6 kJ mol(-1 )at a temperature below 253 K while the E a of Au/ZnO (O-2-xK) was constant, suggesting that the reaction mechanism for Au/ZnO (H-2-xK) changed at 253 K. UV-vis spectroscopy suggested a larger amount of defects of ZnO. Electron paramagnetic resonance results indicated that the amount of oxygen vacancies of ZnO or O-2- radicals formed on the oxygen vacancies was increased by H-2 reduction and heat treatment in air. In temperature-programmed O-2 desorption, a desorption peak was observed at a lower temperature for Au/ZnO (H-2-xK) after heat treatment than that for Au/ZnO (H-2-xK) before heat treatment and Au/ZnO (O-2-xK). These results suggested that the heat treatment of Au/ZnO (H-2-xK) created oxygen vacancies of which O-2 is activated around the perimeter interface and the activated oxygen is easily desorbed. These oxygen vacancies may become more efficient at a low temperature, resulting in the change of the reaction mechanism at 253 K. This study showed that the effect of the perimeter interface on activation of O-2 changes depending on the temperature and can be controlled by catalyst preparation and heat treatment.