Reduced Ni-Mo/Al2O3 catalysts exhibit a behavior analogous to that of sulfided Ni-Mo/Al2O3 catalysts in hydrogenation of linear aldehydes to alcohols. Similar to what has been previously reported for sulfided catalysts, NO and CO2 can be used over the reduced Ni-Mo catalysts as probe molecules for the active sites responsible for two competing reactions-aldehyde hydrogenation to alcohols and condensation reactions to heavy products, respectively. Reduced catalysts have a higher aldehyde conversion activity and alcohol selectivity than their sulfided counterparts. The reduction temperature has a strong effect on the surface density of anion vacancies, which are responsible for alcohol formation. Reduction temperature also plays a role in determining the abundance of OH groups on the alumina surface. The effect of reduction temperature also manifests itself through the differences seen in the oxidation states of Mo and Ni species.