Fibrillar alumina as a wash-coat on monoliths in the catalytic oxidation of xylene

Abstract

Wash-coats of fibrillar boehmite were prepared and used as supports for platinum in catalysts for oxidizing xylene to carbon dioxide and water. Compared with wash-coats of corpuscular boehmite and spherical silica, those of fibrillar boehmite had larger pore sizes in combination with high surface areas. The light-off temperature depended on the amount of fibrillar wash-coat and was lowest for an amount corresponding to a surface area about 35 m 2 per gram of catalyst. The conversion of xylene depended, as expected, on the space velocity but less so than for catalysts with wash-coats of spherical silica and corpuscular boehmite. Hydrothermal treatment of catalysts caused pores smaller than 50Åto disappear, with subsequent loss of surface area and activity in such pores. Platinum was utilized more efficiently by depositing it on a hydrothermally treated wash-coat. In terms of low light-off temperatures and relative independence of space velocity, the catalyst wash-coats could be ranked in order of decreasing efficiency as fibrillar boehmite, spherical silica and corpuscular boehmite.