Physicochemical properties and catalytic performances of Pd catalysts supported on commercial micron-sized and nanocrystalline TiO2 synthesized by sol-gel and solvothermal method were studied for the selective hydrogenation of acetylene in the presence of excess ethylene. While acetylene conversions were found to be merely dependent on Pd dispersion, ethylene selectivity appeared to be strongly affected by the presence of Ti3+, in the TiO2 samples. The use of pure anatase TiO2 (either micron- or nano-sized) that contained significant amount of Ti3+ as supports for Pd catalysts gave high ethylene selectivities, while the use of pure rutile TiO2 (without Ti3+ present) resulted in ethylene loss. The results suggest that the effect of Ti3+ in the TiO2 supports was more important for high ethylene selectivity than the effect of TiO2 crystallite size for selective acetylene hydrogenation over Pd/TiO2 catalysts. (c) 2006 Elsevier B.V. All rights reserved.