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

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 VOx/TiO2, 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 mu m-thick polysiloxane film ending in ca. 1 mu m thick silica after calcination. After studying the textural properties and zeta potential of aqueous suspensions of TiO2 particles, the silica-coated foams were dipped in a 37 wt.% aqueous suspension of TiO2-anatase. The final VOx/TiO2/SiO2/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. (C) 2010 Elsevier Inc. All rights reserved.