A method of partially oxidizing an alcohol to an aldehyde or ketone comprises contacting a gas containing the alcohol with a solid catalyst containing molybdenum, preferably in a +6 oxidation state, and having a surface area of 10 m2/g or higher, preferably 100 m2/g or higher. The molybdenum is supported on a high surface area carrier. The alcohol is a primary or secondary alcohol and preferably contains from 1 to 6 carbon atoms. In a preferred embodiment, the alcohol is ethanol. NOx emissions from an internal combustion engine can be lowered by combining the product of partial oxidation with the exhaust stream before passing the exhaust mixture through a lean NOx catalyst. The partial oxidation product may be generated on board and injected into the exhaust under closed loop or open loop control