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Acid-Promoter-Free Ethylene Methoxycarbonylation over Ru-Clusters/Ceria: The Catalysis of Interfacial Lewis Acid–Base Pair

An, Jinghua, Wang, Yehong, Lu, Jianmin, Zhang, Jian, Zhang, Zhixin, Xu, Shutao, Liu, Xiaoyan, Zhang, Tao, Gocyla, Martin, Heggen, Marc, Dunin-Borkowski, Rafal E., Fornasiero, Paolo, Wang, Feng
Journal of the American Chemical Society 2018 v.140 no.11 pp. 4172-4181
active sites, catalysts, catalytic activity, dissociation, ethylene, hydrogen, methanol, nuclear magnetic resonance spectroscopy, oxygen, palladium, reaction mechanisms
The interface of metal-oxide plays pivotal roles in catalytic reactions, but its catalytic function is still not clear. In this study, we report the high activity of nanostructured Ru/ceria (Ru-clusters/ceria) in the ethylene methoxycarbonylation (EMC) reaction in the absence of acid promoter. The catalyst offers 92% yield of MP with TOF of 8666 h–¹, which is about 2.5 times of homogeneous Pd catalyst (∼3500 h–¹). The interfacial Lewis acid–base pair [Ru-O-Ce-Vö], which consists of acidic Ce-Vö (oxygen vacancy) site and basic interfacial oxygen of Ru-O-Ce linkage, acts as active site for the dissociation of methanol and the subsequent transfer of hydrogen to the activated ethylene, which is the key step in acid-promoter-free EMC reaction. The combination of ¹H MAS NMR, pyridine-IR and DFT calculations reveals the hydrogen species derived from methanol contains Brönsted acidity. The EMC reaction mechanism under acid-promoter-free condition over Ru-clusters/ceria catalyst is discussed.