Masking of either acidic or basic sites of aluminum oxide, by co-feeding of NH3 or CO2, respectively, along with isophorone, indicate the involvement of weak/moderate basic sites to abstract a proton to form an enolate ion followed by involvement of weak/moderate acid sites for dienone-phenol rearrangement to yield aromatization products and involvement of strong acidic sites for yielding decomposition products. (C) 2004 Elsevier B.V. All rights reserved.