III International Conference

PP-II-143XPS, XRD and UV-Vis DRS studies showed that the ionic Au 3+ precursor is decomposedpartially at room temperature with formation of gold clusters which according to data of NMRof adsorbed 129 Xe are stabilized inside the zeolite channels. Sample reduction with hydrogenor their calcination in air at temperatures above 100 o C leads to: (i) reduction of cations Au 3+ ,(ii) formation of nanoparticles with the size 1-10 nm detected with TEM and opticalspectroscopy on the external surface of zeolites, (iii) stable preservation of clusters even attemperatures higher than 300 o C.Catalytic tests in CO oxidation showed difference in reactivity of different gold species.Analysis of catalytic, DRS, XPS, NMR of 129 Xe and TPR results allowed to assign the activesites in low temperature region to gold clusters, stabilized inside the zeolite channels. Thesites active at high temperature were assigned to small nanoparticles. Partially charged goldclusters are the most active in catalytic CO oxidation among gold species incorporated intozeolites. Nanoparticles are stable while clusters are characterized by low stability particular inthe atmosphere of oxygen. Received data could partially explain the discrepancy in the natureof gold active sites described in literature. Various research groups could work underdifferent conditions activating different active sites in the same catalyst.AcknowledgementsAuthors would like to express their gratitude to E. Flores, A. Diaz, E. Aparicio, J. Peralta,I. Gradilla, P. Casillas for technical assistance in experimental work. This work was supportedby CONACYT grant No 42658Q and E120.0862 and by UNAM grants IN 109003 andCOIC-OAI-174-04.References1. M. Haruta, Catalysis Today 36 (1997) 153.2. M. Haruta, S. Tsubota, T. Kobayashi, H. Kageyama, M. J. Genet, B. Delmon, J. Catal. 144 (1993)175.3. D.W. Goodman, Catalysis Letters, 99, 1–2, (2005) 1.4. M. Valden, X. Lai, D. W. Goodman, Science 281 (1998) 1647.5. N. A. Hodge, C. J. Kiely, R. Whyman, M. R. H. Siddiqui, G. J. Hutchings, Q. A. Pankhurst,F. E. Wagner, R. R. Rajaram, S. E. Golunski, Catal. Today 72 (2002) 133.6. A. Simakov, N. Bogdanchikova, I. Tuzovskaya, E. Smoletseva, A. Pestryakov, M. Farias,M. Avalos, in: Proceedings of SPIE: Complex Mediums VI: Light and Complexity, Vol. 5924,Eds. M. W. McCall, G. Dewar, M. A. Noginov, (Bellingham, WA, 2005) p. 592410-1.7. E. Smolentseva, N. Bogdanchikova, A. Simakov, A. Pestryakov, I. Tuzovskaya, M. Avalos,M.H. Farías, J.A. Díaz and V. Gurin, Surf. Sci., (2006) in press.8. E. Smolentseva, N. Bogdanchikova, A. Simakov, V. Gurin, M. Avalos, A. Pestryakov, M. Farias,J.A. Diaz, A. Tompos, Int. J. Modern Phys. 19, (2005) 2496.9. A. Pestryakov, I. Tuzovskaya, E. Smolentseva, N. Bogdanchikova, F. Jentoft, A. Knop-Gericke,Inter. J. of Modern Phys. B, 18, (2005) 2321.10. A.A. Simakov, I. Tuzovskaya, A. Pestryakov, N. Bogdanchikova, V. Gurin, M. Avalos,M.H. Farías, Appl. Cat., [sent for publication].427