Materials chemistry for catalysis: Coating of catalytic oxides on metallic foams

Abstract

Catalytic structured reactors are designed to improve both heat and mass transfers during reactions in the presence of catalytic layers. The know-how acquired in the coating of stainless steel walls by catalytic layers of VO x /TiO 2, active in the abatement of volatile organic compounds and in the production of chemical intermediates, was extended to metallic foams. The preferred and original way was to first make a deposit of a silica-like primer by cold plasma assisted polymerization of tetramethyldisiloxane in the presence of oxygen. After mineralisation, this layer was supposed to act as a barrier against poisoning by elements of the metallic substrate, as well as a stabilizer of the catalyst layers. The cells of the foam were homogeneously covered by a 5 μm-thick polysiloxane film ending in ca. 1 μm thick silica after calcination. After studying the textural properties and zeta potential of aqueous suspensions of TiO 2 particles, the silica-coated foams were dipped in a 37 wt.% aqueous suspension of TiO 2-anatase. The final VO x /TiO 2/SiO 2/foams were obtained by grafting polyvanadate specie in sol–gel medium. At every step of coating, the multilayer materials were studied mainly by X-ray Photoelectron Spectroscopy and Electron Probe Micro-Analysis. Moreover the mechanical and chemical stability of the successive coatings was checked.