CATALYTIC COMBUSTION OVER TRANSITION-METAL OXIDES AND PLATINUM TRANSITION-METAL OXIDES SUPPORTED ON KNITTED SILICA FIBER

A textile made up of an organic-inorganic hybrid fibre containing 70% cellulose and 30% silicic acid was used as a raw material for the preparation of the thermostable support for combustion catalysts. The hybrid textile was burnt to obtain a pure knitted silica fibre. The surface area and crystallinity of this fibre was measured as a function of burning temperature. The knitted silica fibre obtained by burning the hybrid textile at 950-degrees-C was found to have sufficient strength and a high BET specific surface area (almost-equal-to 140m2/g) to be used as a support for the catalysts for catalytic combustion. A series of Co3O4, Pt-Co3O4, Pt-NiO, Co3O4-NiO, Pt-Co3O4-NiO, Cr2O3, Cr2O3-Co3O4, Cr2O3-NiO, Cr2O3-Co3O4-NiO, Pt-Cr2O3-Co3O4-NiO, MnO2, Pt-MnO2 and PtO2 catalysts were prepared by impregnation of the obtained support with solutions of metal salts. The catalytic activities of the catalysts were tested by burning a gas mixture consisting of HC, CO, CO2, NO, water vapour and N2. In each series an increase in the metal oxide content of the catalyst resulted in an improved combustion efficiency. The combination of platinum and metal oxides (Co3O4, NiO, MnO2) increased the conversions of hydrocarbons, carbon monoxide and nitric oxide. Conversions of 98.2% for CO, 99.8% for hydrocarbons and 41% for NO were achieved with a Pt-Co3O4 catalyst at lambda=1.010. The combination of Pt and metal oxides, with the exception of NiO, did not alter the light-off temperatures with respect to the platinum catalyst. The light-off temperatures of the Pt-NiO catalysts were some 40-degrees-C lower than those of the platinum, Pt-Co3O4 and Pt-MnO2 catalysts. The activity patterns for HC and CO oxidation were established.