Effect of addition of vanadium oxide (vanadia) to Rh/SiO2 in hydroformylation of ethylene and CO hydrogenation was investigated. In the hydroformylation of ethylene, the addition of vanadia enhanced hydroformylation activity and selectivity; especially the selectivity for 1-propanol formation was drastically promoted. The promoting effect was observed more significantly on the catalyst calcined at higher temperature such as 973 K. It is found that the effect is related to the formation of the RhVO4 phase, and it is suggested that the active site consists of Rh metal and partially reduced VOx which is formed by the reduction of RhVO4. This can make the interaction between Rh and VOx more intimate. This catalyst was also effective for the alcohol formation in CO hydrogenation. Based on the catalyst characterization by means of the adsorption measurements of H-2 and CO, H-2-D-2 exchange rate under the presence of CO, temperature-programmed desorption (TPD) of CO, temperature-programmed reduction (TPR) with H-2 and temperature-programmed surface reaction (TPSR) of adsorbed CO with H-2, it is suggested that the sites for H-2 activation, which cannot be inhibited by the presence of CO, play an important role in the promotion of alcohol formation in hydroformylation and CO hydrogenation. (c) 2005 Elsevier B.V All rights reserved.