Nickel-nanoparticle-loaded theta-Al2O3 (Ni/theta-Al2O3), prepared by H-2-reduction of NiO/theta-Al2O3, acts as an effective and reusable heterogeneous catalyst for acceptor-free dehydrogenation of alcohols in a liquid phase. Among various supports, amphoteric supports (such as theta-Al2O3), having both acidic and basic sites, gave higher activity than acidic or basic supports. Among Ni/theta-Al2O3 catalysts with different Ni particle sizes, turnover frequency (TOF) per surface Ni increases with decreasing Ni particle size. These results suggest that low-coordinated Ni-0 sites and metal/support interfaces play important roles in the catalytic cycle. The reaction mechanism is investigated by in situ IR study combined with kinetic analysis (kinetic isotope effect), and the following mechanism is proposed: (1) reaction of an alcohol with Lewis acid (Al delta+)-base (Al-O delta-) pair site of alumina yields an alkoxide on the Al delta+ site and a proton on the Al-O delta- site, (2) C-H dissociation of the alkoxide by Ni-0 site to form Ni-H and a ketone, and (3) protolysis of Ni-H by a neighboring proton to release H-2 gas. The proposed mechanism provides fundamental reasons for the higher activity of Ni on the acid-base bifunctional support (Al2O3) than on basic and acidic ones. (C) 2013 Elsevier Inc. All rights reserved.