Catalytic Combustion Over Transition Metal Oxides and Platinum-Transition Metal Oxides Supported on Knitted Silica Fibre

Abstract

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°C was found to have sufficient strength and a high BET specific surface area (≈ 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 γ=l.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°C lower than those of the platinum, Pt-Co₃O₄ and Pt-MnO₃ catalysts. The activity patterns for HC and CO oxidation were established.

Keywords:

• Catalytic combustion
• transition metal oxides
• silica fibre support