Another method of preparing alcohols is the reduction of aldehydes or ketones to alcohols. The simplest method is the hydrogenation of the carbon-oxygen double bond, using hydrogen in the presence of a platinum, palladium, nickel, or ruthenium catalyst.

Ethanal [1]  is transformed by hydrogenation of the double bond into ethanol [2].
Cyclopentanone [1] is transformed by hydrogenation into cyclopentanol [2]