pubs.acs.org/cm Published on Web 05/04/2010 r 2010 American Chemical Society Chem. Mater. 2010, 22, 3313–3315 3313 DOI:10.1021/cm100724f Hydrophobic Polymer-Coated Metal Oxide Catalysts for Effective Low-Temperature Oxidation of CO under Moisture-Rich Conditions Chun-Hu Chen, † Eric C. Njagi, † Shih-Po Sun, ‡ Homer Genuino, † Boxun Hu, § and Steven L. Suib* ,†,§ † Department of Chemistry, ‡ Polymer Program, Institute of Materials Science, and § Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3060 Received March 11, 2010 Revised Manuscript Received April 22, 2010 For the past several decades, the oxidation of carbon monoxide (CO) has become important in numerous app- lications, such as air/gas purification, life-support respira- tors, exhaust pollution reduction for automobiles/factories and Pt electrode protection in the low-temperature fuel cell system. 1 This results in a pressing need for CO oxi- dation catalysis; and many catalyst systems (noble metals, metal oxides, and composites) have been studied for high CO conversion at various temperatures and environments. 2 Among them, metal oxide catalysts with low production costs and high CO oxidation activity proved to be the most attractive. Most CO oxidation applications involve moist envi- ronments with rapid flow rates, so highly moisture tolerant catalysts are necessary. Noble metal catalysts are known to be less susceptible to water and have been successfully applied in motor vehicles, but high production costs hinder their wider applications. Most of the inexpensive and highly active metal oxide catalysts, such as Co 3 O 4 , on the other hand are rapidly deactivated with trace amounts of moisture (3-10 ppm moisture level) from the feed gas. The super dry conditions (<1 ppm moisture level), crea- ted by passing the feed gas through molecular sieve traps at dry ice temperature (-77 °C) is required to avoid water deactivation. 3,4 This pretreatment, however, is not appli- cable for most applications. Other studies show that the incorporation of CeO 2 into metal oxide catalysts can improve the water tolerance by decomposing water mole- cules via the water-gas shift reaction (WGSR). 5 Never- theless, this approach is limited to a specific material (CeO 2 ) and the occurrence of WGSR at temperatures higher than 110 °C. Studies show that the surface hydrophobicity/hydro- philicity and membranous modification utilizing poly- mers is a promising strategy to enhance the selectivity, conversion, and recyclability of catalysts in many systems. 6 Our previous work shows that the polydimethylsiloxane (PDMS) coated nanostructured manganese oxide mate- rials exhibit a superhydrophobicity and highly selective adsorption of organic molecules in the presence of water. 7 Accordingly, hydrophobic PDMS coatings on metal oxi- des prevent water from deactivating metal oxide catalysts. Although numerous attempts focusing on intrinsic modi- fication of catalysts to address water deactivation at low temperatures, 3,5 the idea of introducing a protective layer with high hydrophobicity on the catalysts has not been reported yet. Here, we demonstrate the first example of the prepara- tion and evaluation of a highly water-tolerant, hydro- phobic polymer coated metal oxide catalyst for CO oxi- dation. The harsh experimental conditions, high moisture level (∼3%), high space velocity (35 000 mL h -1 g cat -1 ) and low oxygen content (2%) in the feed gas were investigated to evaluate the catalytic performance for rapid air purification. 8 Well-studied catalysts with vari- ous compositions, crystallinity, and surface areas, e.g. commercial product Hopcalite (HOP, CuMnO x ), amor- phous manganese oxide (AMO), and crystalline cobalt oxide (COX, Co 3 O 4 ) were selected to examine the gene- rality of this hydrophobic surface coating approach. 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