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Platinum metal was dispersed on microporous, mesoporous, and nonporous support materials including the zeolites Na-Y, Ba-Y, Ferrierite, ZSM-22, ETS-10, and ALP0-11, alumina, and titania. The oxidation of carbon black loosely mixed with catalyst powder was monitored gravimetrically in a gas stream containing nitric oxide, oxygen, and water. The carbon oxidation activity of the catalysts was found to be uniquely related to the Pt dispersion and little influenced by support type. The optimum dispersion is around 3–4% corresponding to relatively large Pt particle sizes of 20–40 nm. The carbon oxidation activity reflects the NO oxidation activity of the platinum catalyst, which reaches an optimum in the 20–40 nm Pt particle size range. The lowest carbon oxidation temperatures were achieved with platinum loaded ZSM-22 and AIPO-11 zeolite crystallites bearing platinum of optimum dispersion on their external surfaces. [ABSTRACT FROM AUTHOR]

Abstract: 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 NO x , 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 NO x . [Copyright &y& Elsevier]