Possible Role of Isocyanate Species in NOx Reduction by Hydrocarbons Over Copper-Containing Catalysts.

The behavior of an isocyanate intermediate (-NCO) formed during NOx reduction has been studied on alumina-supported CuCs oxide catalyst in the presence of oxygen and hydrocarbons (propene, acetylene, propane and n-heptane) using infrared spectroscopy. While a reaction involving NO, O2 and acetylene needs some heat treatment to produce the isocyanate species on the catalyst, no heat treatment is required in the NO/O2/propene or n-heptane system. No isocyanate intermediate is formed in a NO/O2/propane system by an ordinary procedure. Adsorbed water on the catalyst surface is found to suppress the formation of the isocyanate species. This inhibition effect is smaller in the acetylene or n-heptane containing system than in the propene containing system. The role of isocyanate species is discussed with reference to results for the practical reduction of NOx.