Heterogeneous catalysis is a key technique to achieving chemical transformation with high efficiency and selectivity, in which designing and controlling the structures of active sites and reaction environments holds the promise. Most recently, the research group led by Prof. XIONG Yujie demonstrated that charge polarization at metal-oxide interfaces could play a vital role in gas-phase reactions through collaborations with Profs. JIANG Jun and HUANG Weixin. This progress has been published in J. Am. Chem. Soc. 2014, 136, 14650.
Schematic illustrating the improvement of CO oxidation by interfacial polarization in metal-oxide hybrid structures
In a heterogeneous catalysis reaction, charge transfer typically occurs between adsorbed species and catalyst surface. The efficiency of such charge transfer is dependent on the surface charge density of catalysts, opening possibilities to tuning catalytic performance. In the past years, tremendous efforts have been made to control the surface facets of catalytic materials; however, it remains a grand challenge to arbitrarily tailor the surface charge state of these solid materials. In a previous study, the researchers demonstrated using two-dimensional systems as model structures that the difference in work functions may result in surface polarization when two different materials contact each other, tuning charge state to improve catalytic performance (Angew. Chem. Int. Ed. 2014, 53, 12120). However, such surface polarization can effectively take place only when the layer thickness of catalytic materials is confined at the atomic level, which thus generally requires expensive atomic layer deposition (ALD) technique for the fabrication of such structures.
To address this grand challenge, the researchers have designed a class of metal-oxide hybrid structures with exposed interfaces and developed methodology for precisely controlling their interfacial parameters, producing a series of hybrid structures with tunable interfacial lengths. In these unique hybrid structures, the interfacial polarization between metal and oxide induced the accumulation of negative charges on the oxide surface next to interfacial lines, overcoming the limitation that polarization charges had to travel through the upper-layer film in two-dimensional models. Taking CO oxidation as a model reaction, the researchers found that the interfacial polarization could lower the energy barrier for CO activation on the oxide surface, making the one-dimensional interfaces as reaction active sites. The controllability over the interfacial lines thus enables to tune the number of active sites and in turn the catalytic conversion rates. This work opens up a new strategy for the design of efficient and economic oxide-metal catalysts through interface engineering.
This work was supported by 973 Program, NSFC, Hok Ying Tung Education Foundation, Specialized Research Fund for the Doctoral Program of Higher Education, Recruitment Program of Global Experts, CAS Hundred Talent Program, and Fundamental Research Funds for the Central Universities.
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