CHINESE JOURNAL OF CATALYSIS Volume 28, Issue 5, May 2007 Online English edition of the Chinese language journal Cite this article as: Chin J Catal, 2007, 28(5): 463–468. Received date: 2006-11-28. * Corresponding author. Tel: +86-10-62794468; E-mail: wangdz@flotu.org Copyright © 2007, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier BV. All rights reserved. RESEARCH PAPER Effect of Doped Ag on Performance of Manganese Oxide Octahedral Molecular Sieve for CO Oxidation HU Rongrong 1 , CHENG Yi 1 , XIE Lanying 2 , WANG Dezheng 1, * 1 Department of Chemical Engineering, Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology, Tsinghua University, Beijing 100084, China 2 Technology Center of China Tobacco Hunan Industrial Corporation, Changsha 410001, Hunan, China Abstract: A series of Ag-doped manganese oxide octahedral molecular sieves (OMS-2) were synthesized by the reflux method in an acid medium. The structure of the catalysts was characterized by X-ray diffraction, N 2 adsorption, transmission electron microscopy, and temperature-programmed desorption (TPD). The effect of the promoter Ag was deduced. The results showed that the catalysts have the typical cryptomelane structure with a one-dimensional channel. The doping with Ag resulted in Ag/OMS-2 catalysts with a higher spe- cific surface area and narrower pore size distribution than OMS-2. The catalysts showed excellent catalytic activity for CO oxidation and the catalytic activity was increased after Ag introduction. O 2 -TPD and CO-TPD results showed that this was because the doping with Ag increased the rate of CO adsorption and the diffusion of lattice oxygen ions. Key Words: manganese oxide; octahedral molecular sieve; silver; carbon monoxide; oxidation CO oxidation is of practical importance for controlling the CO poison that comes from incomplete combustion processes, e.g. cigarette combustion. In recent decades, with the rapid development of new materials and new techniques, the cata- lytic oxidation of CO has become an important research topic since it has many applications, such as indoor air cleaning, fuel cells, CO gas sensors, and gas purification of CO 2 lasers [1–3]. Precious metal catalysts, such as Pd, Pt, and Au, and re- ducible transition metal oxide catalysts are two typical cata- lysts for the CO oxidation [4–9]. It is widely agreed that the CO catalytic oxidation follows a redox mechanism on the surface of metal oxide catalysts [4,5], that is, the lattice oxy- gen reacts with adsorbed CO and the gas oxygen replenishes O vacancies that are formed by lattice oxygen. The catalytic oxidation of CO on precious metal catalysts then follows a Langmuir–Hinshelwood mechanism [5,6] and the surface reaction occurs between adsorbed CO and dissociatively ad- sorbed oxygen. However, the reaction mechanism of CO oxi- dation on supported Au catalysts is more complex. It was suggested that CO oxidation occurs when CO adsorbs onto a metallic Au site adjacent to a metal–oxide site or the gold and metal–oxide interface occupied by an adsorbed O 2 molecule, with the catalytic reaction proceeding via immigrating of the adsorbed oxygen to gold surface and forming an intermediate carbonate-like species that decomposes to CO 2 when it de- sorbs from the surface [8,9]. Though people have more comprehensive knowledge about the reaction mechanism of the catalytic oxidation of CO in the field of heterocatalysis science, the finding of many new phe- nomena makes the knowledge develop and complete. For example, it was found that the CO oxidation activity of transi- tion metal oxides would be improved when doping precious metal in them, e.g. doping Ag [10] or Au [11] in ferric oxide, and the Schottky effects between metal oxide and metal could promote the adsorption of CO and oxygen, which is helpful for the research and development of cheap metal oxide cata- lysts instead of expensive precious metal catalysts for CO oxidation. The manganese oxide octahedral molecular sieve (OMS-2) is an effective green oxidation catalyst, and its crystal struc- ture consists of 2 × 2 edge-shared MnO 6 octahedral chains, which are corner-connected to form one-dimensional channels of ca. 0.46 nm × 0.46 nm. OMS-2 has been now mainly used in catalytic oxidation of some pollutants such as CO [12], phenol [13], methanol [14], and cyclohexanol [15]. Xia et al.