The strong metal-support interaction and catalytic behaviors of Pd catalysts supported on micron(0.1 mu m)- and nano-sized (14 nm) TiO2 were investigated in the liquid-phase selective hydrogenation of phenylacetylene to styrene. It was found that when supported on the nano-sized TiO2, the Pd/TiO2 catalyst that reduced by H-2 at 500 degrees C exhibited strong metal-support interaction (SMSI) and much improved catalytic performance in liquid-phase selective hydrogenation of phenylacetylene. However, as revealed by CO pulse chemisorption, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and CO-temperature program desorption, the SMSI effect was not detected for the micron-sized TiO2 supported ones. It is suggested during high-temperature reduction, the inner Ti3+ in large crystallite size TiO2 was more difficult to diffuse to the Pd-0 surface than the surface Ti3+ in the smaller crystallite size ones. Sintering of Pd-0 metal was observed instead. (c) 2007 Elsevier B.V. All rights reserved.