Dehydrogenation of propane to propylene in the presence or absence of carbon dioxide was performed over a series of mixed GaxAl10-xO15 oxides (with x varying from 0 to 10) synthesized through an alcoholic coprecipitation pathway. Among the various compositions of GaxAl10-xO15, the maximum activity was observed for x = 8. Whereas the same tendency was observed for the specific activity normalized by BET surface area, significantly enhanced stability was achieved for Ga2O3-Al2O3 with higher aluminum content. A correlation between the NH3-TPD results and the initial activity for GaxAl10-xO15 reveals that a high population of surface acid sites related to tetrahedral Ga3+ cations is important to achieving high activity. The specific interaction between Ga2O3 and Al2O3 due to the formation of spinel-type gamma-Ga2O3Al2O3 solid solutions is suggested to play a key role in the dispersion and distribution of surface gallium sites, which makes GaxAl10-xO15 composites highly active and stable for the reaction. (c) 2008 Elsevier Inc. All rights reserved.