The effect of potassium (K) addition on the performance of a TiO2-modified Pd catalyst in the hydrogenation of acetylene was investigated. When K was added to Pd-Ti/SiO2, the resulting catalyst showed an improved selectivity for ethylene production over a wide range of conversions. when the catalyst was reduced at 300degreesC. This is in contrast to the case of K-free Pd-Ti/SiO2, which showed an improved selectivity only when the catalyst was reduced at high temperatures, e.g. 500degreesC. Analyses of the catalyst surface using infrared, X-ray photoelectron spectroscopy and CO chemisorption indicate that the K-containing Pd surface is modified with the Ti species after the catalyst is reduced at relatively low temperatures. The origin of the facilitated modification is the formation of potassium titanates, which have a lower melting point than that of TiO2 and therefore migrate onto the Pd surface after the catalyst is reduced at lower temperatures compared to the case of TiO2. (C) 2004 Elsevier B.V. All rights reserved.