The catalytic properties of two series of Au/TiO2 catalysts prepared by deposition-precipitation with NaOH (DP NaOH) (similar to3 wt%) and by deposition-precipitation with urea (DP Urea) (similar to8 wt%) were evaluated for the reaction of crotonaldehyde hydrogenation at atmospheric pressure. There is no difference in activity (mol g(Au)(-1) s(-1)) and selectivity between the DP Urea and DP NaOH samples for a given activation treatment. This is due to the fact that the DP Urea and DP NaOH samples exhibit a similar gold particle size distribution, although the gold loading in DP Urea catalysts is much higher than in DP NaOH. The DP Urea samples were reduced under H-2 at different temperatures (120500 degreesC) or treated in air at 300 degreesC with various flow rates, to vary the average particle size within a large range, 1.7 to 8.7 nm. The selectivity to crotyl alcohol (selective hydrogenation of the carbonyl bond), in the 5-50% conversion range, is high, 60-70%, and is independent of the reduction temperature, and almost constant as a function of the particle size. In contrast, the TOF depends on the gold particle size, drastically increasing when the gold particle size is similar to2 nm. These characteristic features of Au/TiO2 catalysts in this reaction are compared with those of Pt/TiO2. The possible adsorption modes of crotonaldehyde are discussed. Hydrogen dissociation is proposed to be the rate-determining step, and to take place on the low-coordinated atoms of the gold particles. (C) 2004 Elsevier Inc. All rights reserved.