In-depth study on propane dehydrogenation over Al2O3-based unconventional catalysts with different crystal phases

•The effect of crystal phase of Al2O3 on dehydrogenation performance was studied.•The type of the active sites is the same for Al2O3 with different phases.•Different performances result from various surface densities of the active sites.•The active sites for propane dehydrogenation are some specific Lewis acid sites.•Coordinatively unsaturated AlⅣ species are responsible for propane dehydrogenation.