III International Conference

PP-II-143CATALYTIC ACTIVITY OF DIFFERENT GOLD SPECIES IN HIGH-SILICATEAND LOW SILICATE Au-MORDENITESTuzovskaya I. ∗ , Bogdanchikova N., Simakov A., Pestryakov A. 1 , Farías M., Gurin V. 2 ,Avalos M.Centro de Ciencias de la Materia Condensada, Universidad Nacional Autónoma de México,Apdo. Postal 2681, C. P. 22800, Ensenada, Baja California, México1 Tomsk Polytechnic University, Tomsk, Russia2 Physico-Chemical Research Institute, BSU, Minsk, BelarusE-mail: nina@ccmc.unam.mxIt was disclosed for Au/zeolites that not one, but several active sites can be reactive inCO-oxidation on the same catalyst. Au 3+ cationic species does not show the activity understudied conditions. Gold nanoparticles (1.5-5 nm) are characterized by activity at hightemperature. Gold clusters (≤ 0,7 nm) display activity in low-temperature region, but onlyafter sample pretreatment in He at 500 o C. The clusters lost the activity during reactionprobably due to oxidation and can be reactivated by He treatment while nanoparticles arestable to redox treatment at high temperature. Received data can explain the contradictionconcerning the nature of active sites existing in the literature.An intensive study of gold in catalysis for last decade was stimulated by discovery ofunique activity of gold nanoparticles at low temperature for several reactions such as COoxidation [1]. However, the origin of this unusual behavior of gold remains still under debate.A number of gold active sites were proposed: gold-support interface [2], the second layer ofgold atoms from the support [3], gold nanoclusters with nonmetallic electronic properties dueto a quantum-size effect [4], Au 3+ ions [5], etc.The effect of multiplicity of Au active sites in one catalyst and their activation underdifferent conditions was revealed in our previous studies [6-9]. In this work the data aboutactive sites for high-silicate and low-silicate zeolites will be considered, and how the dataabout the nature of active sites could explain discrepancy in the literature [10].AuM206 sample was prepared by ion exchange procedure of protonic mordenite (TOSOHCorporation, Japan, SiO 2 /Al 2 O 3 molar ratio (MR) = 206) with aqueous [Au(NH 3 ) 4 ](NO 3 ) 3complex at room temperature. Samples were dried at room temperature for 24 hours.Au/zeolites were studied by different physicochemical methods to reveal the active sites inCO oxidation.∗On leaving from Tomsk Polytechnic University, Tomsk, Russia426