Catalytic carbon oxidation over Ag/Al2O3

The potential of silver on alumina (Ag/Al2O3) catalyst for the oxidation of carbon particles in simulated lean combustion gas was explored. At low temperatures in the presence of NOx, oxygen, and water, the silver of the catalyst is transformed into silver nitrate. On heating, finely dispersed silver metal is formed that catalyzes the oxidation of NO into NO2. The carbon oxidation rates in loose mixtures of carbon black and nitrated Ag/Al2O3 catalyst were determined gravimetrically using a magnetic suspension balance and gas mixture comprising nitric oxide, oxygen, and water. The temperature for achieving carbon oxidation was lower with nitrated Ag/Al2O3 than with Pt/Al2O3. The finely dispersed metallic state of the silver required for efficient NO oxidation can be regenerated in cycles involving cooling and heating in the presence of NOx.