Probing the Mechanism of Low-Temperature CO Oxidation on Au/ZnO Catalysts by Vibrational Spectroscopy

详细信息    查看全文

• 作者：Heshmat Noei ; Alexander Birkner ; Klaus Merz ; Martin Muhler ; Yuemin Wang
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：May 24, 2012
• 年：2012
• 卷：116
• 期：20
• 页码：11181-11188
• 全文大小：489K
• 年卷期：v.116,no.20(May 24, 2012)
• ISSN：1932-7455

文摘

Adsorption and oxidation of CO on Au/ZnO catalysts were studied by Fourier transform infrared (FTIR) spectroscopy using a novel ultra-high-vacuum (UHV) system. The high-quality UHV-FTIRS data provide detailed insight into the catalytic mechanism of low-temperature CO oxidation on differently pretreated Au/ZnO catalysts. For the samples without O₂ pretreatment, negatively charged Au nanoparticles are identified which exhibit high reactivity to CO oxidation at 110 K, yielding CO₂ as well as carbonate species bound to various ZnO facets. O₂ pretreatment leads to formation of neutral Au nanoparticles where CO is activated on the low-coordinated Au sites at the interface. Activation of impinging O₂ occurs at the Au/ZnO interface and is promoted by preadsorbed CO forming an OC鈥揙₂ intermediate complex, accompanied by charge transfer from Au/ZnO substrate to O₂. The CO molecules adsorbed on ZnO serve as a reservoir for reactants and are mobile enough at 110 K to reach the Au/ZnO interface where they react with activated oxygen yielding CO₂. Different carbonate species are further produced via interaction of formed CO₂ with surface oxygen atoms on ZnO. It was found that the active interface sites are slowly blocked at 110 K by the inert carbonate species, thus causing a gradual decrease of the catalytic activity.