Tuning Catalytic Selectivity of Oxidative Catalysis through Deposition of Nonmetallic Atoms in Surface Lattice of Metal Oxide

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• 作者：Juanjuan Liu ; Shiran Zhang ; Yan Zhou ; Victor Fung ; Luan Nguyen ; De-en Jiang ; Wenjie Shen ; Jie Fan ; Franklin Feng Tao
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：July 1, 2016
• 年：2016
• 卷：6
• 期：7
• 页码：4218-4228
• 全文大小：787K
• 年卷期：0
• ISSN：2155-5435

文摘

Catalytic selectivity for producing an ideal product is a key topic for chemical transformations through heterogeneous catalysis. Tuning catalytic selectivity by integrating the second metal to form an alloy has been well demonstrated in the literature. Here we report a method to tune catalytic selectivity in oxidative catalysis on another category of heterogeneous catalysts, transition-metal oxides. By choosing the oxidative dehydrogenation (ODH) of ethane to ethylene as a probe reaction, we demonstrated that doping nonmetallic atoms to the surface lattice of catalyst of a transition-metal oxide can enhance catalytic selectivity through suppression of complete oxidation of the reactant molecules. Catalysts of Co₃O₄ with doped silicon atoms (Si_x-Co₃O₄) maintaining the spinel structure of pure Co₃O₄ exhibit much higher selectivity for the production of ethylene through ODH of ethane in comparison to pure Co₃O₄ at 600 °C by 40%. The suppression of activity of surface lattice oxygen atoms was evidenced by the observation that the surface lattice oxygen atoms of Si_x-Co₃O₄ cannot exchange oxygen atoms with gas-phase oxygen at low temperatures while pure Co₃O₄ can. The difference in releasing surface lattice oxygen atoms and dissociating molecular oxygen between pure Co₃O₄ and Si_x-Co₃O₄ was supported by DFT calculations. The calculated activation barriers for dissociation of molecular O₂ and energy barriers for hopping surface oxygen vacancies of Si_x-Co₃O₄ are obviously higher than those of pure Co₃O₄, respectively. These experimental exploration and computational studies established a correlation between increase of catalytic selectivity and suppression of the activity of surface lattice oxygen atoms/oxygen vacancies. This correlation suggests an approach for increasing the catalytic selectivity of oxidative catalysis through suppressing activity of surface lattice oxygen atoms/vacancies via doping atoms of a nonmetallic element. This new approach was further confirmed by the observed higher catalytic selectivity for production of ethylene on Ge_0.2-Co₃O₄ in comparison to pure Co₃O₄.