Hydrogenation of citral (3,7-dimethyl-2,6-octadienal) was carried out in a batch reactor at atmospheric hydrogen pressure and 70 A degrees C over Sibunit (mesoporous carbon) supported iridium catalysts with different metal loadings. The major products were isopropyl ethers of geraniol and nerol (2-propanol was used as solvent), but also geraniol, nerol, citronellal di-isopropyl acetal and citronellal were formed. The metal particle size was determined by CO-chemisorption and varied from 2 to 6 nm. The turnover frequency for hydrogenation reactions increased with the metal particle size. Turnover frequency of hydrogenation reactions as a function of particle size.