Characterization of Rh/Al2O3 catalysts after calcination at high temperatures under oxidizing conditions by luminescence spectroscopy and catalytic hydrogenolysis

Rhodium/alumina catalysts with Rh loadings of 0.01-0.5 wt.% with substantially different thermal stability of supports with respect to phase transformation to corundum were studied. It was shown that the stability of alumina support with respect to its transformations to corundum is one of the important factors accounting for irreversible deactivation of Rh/Al2O3 catalysts. We used laser-induced luminescence (LIL) of Cr3+ impurity and Rh3+ in alpha-Al2O3 and XRD for studying catalysts with different calcination temperatures. Catalytic ethane hydrogenolysis was used as a test for Rh loading on the catalyst surface. This method reliably detects Rh ions on the surface starting from concentrations as low as 0.01%. The results of LIL spectroscopy indicated that in all cases Rh3+ ions were incorporated in the bulk of the newly formed alpha-Al2O3 phase, and quite possible can initiates the formation of the corundum phase in catalysts with high-thermal stability. (C) 2009 Elsevier B.V. All rights reserved.