Mesoporous titania–alumina mixed oxide: A preliminary study on synthesis and application in selective catalytic reduction of NOx

Titania–alumina mixed oxide was synthesized hydrothermally using tetrapropylammonium hydroxide (TPAOH) as the template. The dried, calcined and palladium loaded samples were characterized for particle morphology, weight loss, nitrogen adsorption/desorption at liquid nitrogen temperature, texture and metal dispersion. The Pd loaded material was tested for NO reduction in a fixed bed catalytic reactor using a simulated gas mixture closely resembling lean burn engine exhaust. Scanning electron microscopy of the dried and calcined samples revealed a well developed tubular fibrous network of titania–alumina. Thermogravimetry (TG) of the dried sample indicated about 16% weight loss due to decomposition of an oxy-hydroxide structure of the material, mostly boehmite, which was confirmed by X-ray diffraction (XRD) measurements. The boehmite phase changed to poorly crystalline γ-alumina upon calcination where as titania remained as anatase. BET specific surface area, adsorption–desorption isotherms and BJH pore size distributions indicated formation of a mesoporous structure. The surface area of the dried material increased when calcined at 600 °C but the pore size distribution patterns for the dried, calcined and palladium dispersed materials remained unchanged. These observations along with TG and XRD analyses suggest that a thermo-resistant, mesoporous, high surface area, crystalline titania–alumina framework can be prepared using the hydrothermal synthesis route. A peak NOx conversion of 75% with the palladium dispersed catalyst indicates high catalytic activity, possibly due to high dispersion of Pd confirmed by CO chemisorption studies.