Preparation and characterization of VO x/TiO 2 catalytic coatings on stainless steel plates for structured catalytic reactors

Abstract

The parameters to be controlled to coat metallic walls by VO x /TiO 2 catalysts which are used in the mild oxidation of hydrocarbons and NO x abatement are studied. Stainless steel (316L) was chosen because of its large application in industrial catalytic reactors. TiO 2 films on stainless steel were obtained by dip-coating in two steps. Superficially oxidized plates were first dipped in Ti-alkoxide sol–gel to be coated by a very thin layer of TiO 2. On this anchoring layer was then deposited a porous film of titania by dipping plates in an aqueous suspension of TiO 2 particles. After calcination, VO x species were grafted to TiO 2/SS plates and their loading was determined by means of X-ray photoelectron spectroscopy. The chemical and mechanical resistances of films were controlled by several tests. Laser Raman spectroscopy, X-ray diffraction and scanning electron microscopy were used to characterize the samples after each step of preparation. The porous texture was determined using a thermobalance. The dispersion and the nature of VO x species and the value of theoretical monolayer of VO x on TiO 2/stainless steel are shown to depend on the surface V/Ti ratio, in the same manner as for VO x /TiO 2 coating anodised aluminum plates and as for VO x /TiO 2 powders. Therefore, we have demonstrated that the shaping of TiO 2 has no influence on the characteristics of the active phase, which is of prime importance for catalytic applications in structured reactors.