Powder Characteristics and Three-Way Catalytic Activity of Hollow Alumina Made by the Emulsion Combustion Method

Lanthanum-doped hollow alumina particles (A-E) were made by the emulsion combustion method (ECM). Powder characteristics and three-way catalytic performance were evaluated and compared with those of precipitation-made alumina (A-P). The A-E powder was gamma alumina and 40 m2/g in specific surface area (SSA). The unique hollow structure resulted in a broad peak at 130 nm in the pore size distribution and a large pore volume (3.0 cm3/g) with pore diameters of >20 nm. The A-E powder primarily maintained its shape, crystalline phase and SSA up to 1200°C, indicating high thermal stability. Conversion of total hydrocarbon (THC) started at higher temperatures for the Rh-loaded A-E pellets (Rh/A-E) than for Rh-loaded A-P pellets (Rh/A-P) because of the low dispersion of Rh for Rh/A-E. However, a gradient of the THC conversion-temperature curve was higher for Rh/A-E than for Rh/A-P. The large pore volume can promote good gas accessibility inside the pellets for Rh/A-E, resulting in the high gradient of the THC conversion-temperature curve and thus the high activity at high temperatures where gas diffusion is likely to determine the conversion efficiency. The conversion-temperature curves of CO and NOX showed primarily similar behavior to the THC ones.