Aqueous Catalytic Disproportionation and Oxidation of Nitric Oxide

Nitric oxide, a byproduct of combustion exhaust, is a key species that leads to urban photochemical smog. Nitric oxide exhibits low aqueous solubility, and it has proved difficult to remove NO from gas streams by aqueous scrubbing methods. A catalyst for the aqueous disproportionation of NO to nitrous oxide and aqueous nitrite has been developed with wood-derived activated carbons. Addition of palladium or platinum metal to the carbon support significantly accelerates catalysis. The carbon-supported catalyst was not poisoned by sulfur oxides. The reaction is thought to involve the reduction of surface-bound nitric oxide dimers. The reducing equivalents stem from the oxidation of NO to NO2-. Addition of oxygen as an alternative electron acceptor during the reaction immediately arrested nitrous oxide formation, and all the nitric oxide was removed from the gas stream as aqueous nitrite. This demonstrates the feasibility of removing SOx and NOx simultaneously by low-temperature aqueous scrubbing.