A series of RuMo/Al2O3 catalysts was prepared, The Mo loadings were between 0.15 and 0.58 wt.%, while the Ru content was constant at 0.6 wt.% Ru. The catalysts were characterised by electron spin resonance spectroscopy (ESR), infrared spectroscopy of adsorbed CO and temperature-programmed reduction (TPR). n-butane hydrogenolysis was chosen as the catalytic probe. A Ru electron enrichment is suggested to take place in Ru-Mo catalysts. This effect increases the activity for the hydrogenolysis of n-butane and the selectivity towards ethane (for low Mo contents). A downward shift for the adsorbed CO on the RuMo (0.15%)/Al2O3 catalyst compared with the monometallic system (similar to 40 cm(-1)) is in line with such an electron transfer. ESR and TPR results showed that Mo is more easily reduced in the presence of Ru, probably due to a spillover effect. This would increase the likelihood of an electron transfer from partially reduced Mo species to the Ru centres.