abstracts - Институт катализа им. Г.К. Борескова

KS-I-6This finding implies that industrial catalysts should be prepared to maximize the Pd surfacearea without consideration of the cluster shape. On the other hand, the reaction rate showshysteresis behaviour between 600 and 700 K and between 800 and 900 K. Thus during theheating ramp, the methane conversion starts at >500 K and reaches a maximum at 650 K andthen decreases. The maximum of the reaction rate is not observed during the low temperatureramp. The in situ XPS highlighted that during the heating cycle the 2D oxide forms and this isan active phase for methane oxidation. During cooling ramp no oxide phase can be observedand therefore the catalyst shows a low activity. The high-temperature hysteresis likelyassociates with the O γ phase. Below 820 K thermodynamic equilibrium is shifted towards O γbut at higher temperatures diffusion in the bulk becomes essential and O β starts to dominate.Conclusive Remarks: Dissolution of small molecules such as carbon and oxygen can changecatalytic activity of palladium, leading to passivation or activation of the catalyst. Dissolutionis the important step of the reaction mechanism.References:[1] G. Zhu, J. Han, D.Y. Zemlyanov and F.H. Ribeiro, Journal of the American ChemicalSociety 126 (2004) 9896.[2] R. Burch, F.J. Urbano and P.K. Loader, Appl. Catal., A 123 (1995) 173.[3] J.N. Carstens, S.C. Su and A.T. Bell, J. Catal. 176 (1998) 136.[4] R.S. Monteiro, D. Zemlyanov, J.M. Storey and F.H. Ribeiro, J Catal. 199 (2001) 291.[5] H. Gabasch, W. Unterberger, K. Hayek, B. Klötzer, E. Kleimenov, D. Teschner,S. Zafeiratos, M. Havecker, A. Knop-Gericke, R. Schlögl, B. Aszalos-Kiss andD. Zemlyanov, in preparation).[6] D. Zemlyanov, B. Aszalos-Kiss, E. Kleimenov, D. Teschner, S. Zafeiratos, M. Havecker,A. Knop-Gericke, R. Schlögl, H. Gabasch, W. Unterberger, K. Hayek and B. Klötzer, inpress Surface Science.36