NO Reduction by CO Catalyzed with Au/TiO 2 in Oxygen-rich Condition
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NO Reduction by CO Catalyzed with Au/TiO2 in Oxygen-rich Condition J. A. Wanga,*, J. A. Toledob, C. Angelesb, M. Moran-Pinedab, A. García-Ruizc a
ESIQIE, Instituto Politécnico Nacional, Col. Zacatenco, C. P. 07738, México D.F., Mexico Programa de Ingenería Moleciular, Instituto Mexicano del Petróleo. Eje Lázaro Cárdenas 152, C. P. 07730, México D. F., Mexico c UPIICSA, Instituto Politécnico Nacional, Te 950, Col. Granjas-México, Iztacalco, 08400, México, D. F. Mexico b
ABSTRACT Gold nanoparticles supported on titania catalysts with different Au loadings were prepared and evaluated in the reaction of NO reduction by CO in an oxygen rich condition. The crystalline structures of the Au/TiO2 materials were refined with Rietveld method. TiO2 support chiefly contains anatase phase, having a crystalline size ranged from 5 to 15 nm. Au particles have an average crystal size approximately 2-5 nm as Au concentration less 3 wt %. In the reaction of NO + CO + O2, the Au/TiO2 catalysts show a selectivity to 100 % N2, neither NO2 nor N2O was yielded in the reaction temperature between 25 and 400 ºC, which strongly indicates that Au/TiO2 catalysts are much superior to the other catalysts like Pt/TiO2 catalysts on which N2O was usually produced in the reaction temperature below 200 °C and NO2 was produced in the reaction temperature above 300 °C under a similar reaction condition. Keywords: Titania, NO reduction, CO oxidation, sol-gel synthesis, Au/TiO2, catalysts. 1. INTRODUCTION Copper, silver and gold are elements in the same group VIIB, among these elements, Cu and Ag are widely applied as active phases to catalyze many reactions; however, less attention is paid on gold due to its chemical stability and less reactivity in bulk. Recent years, it has been found that when Au is dispersed on a proper support in nanoscale, some unique properties may be exhibited [1, 2]. When gold nanoparticles are entrapped within the pores of the Si-based MCM-41 materials, it shows good catalytic activity and selectivity in the hydrogenation of unsaturated hydrocarbons like hydrogenation of styrene to ethylbenzene [3, 4]. In the low temperature oxidation of CO, gold nanoparticles despersed on a variety of oxides supports show interesting catalytic properties. Exceptionally high activities have been reported for finely dispersed Au on reducible oxides such as TiO2, Fe2O3, Co3O4 and CeO2-ZrO2 in the reaction of CO oxidation at low reaction temperatures [5, 6]. The Au/ceria catalyst also shows high activity in the reactions of methanation and low temperature water-gas shift [7, 8]. Au supported on ZnO and ZrO2 oxides for WGS reaction has been also reported [9]. Sakuria et al. once report that Au/TiO2 catalyst prepared by deposition-precipitation technique is rather active in the low temperature shift reaction [10]. The aim of the present work is to apply Au/TiO2 catalysts for NO reduction with CO in an oxygen rich condition. Catalytic evaluation shows that Au/TiO2 catalysts are very active for NO reduction and CO oxidation and it is superior to the
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