Coating metallic foams and structured reactors by VOx/TiO2 oxidation catalyst: Application of RPECVD

VOx/TiO2, catalyst of oxidative dehydrogenation of propane, was immobilised on a SiO2 film coating stainless-steel (SS) plates and foams figuring out structured reactors. SiO2 is expected to act as a primer and a barrier against poisoning of VOx/TiO2 catalyst by elements of SS. The adhesive SiO2 layer was first coated on 2D- (plates) and 3D-SS substrates (foams) A good adhesion was obtained after polymerisation by RPECVD (Remote Plasma Enhanced Chemical Vapor Deposition) of a 6 mu m-thick tetramethyldisiloxane polymer layer, followed by calcination (650 degrees C) to obtain the SiO2 layer. A post-treatment in N-2/1.5%O-2 plasma afterglow was necessary to eliminate remaining carbon traces after calcination. The resulting SiO2/SS objects were dip-coated in TiO2-anatase aqueous suspension. Vanadium isopropoxide was grafted on calcined TiO2/SiO2/SS, yielding VOx polyvanadates after calcination at 450 degrees C. The mechanical stability of the VOx/TiO2 catalyst immobilized onto SiO2/SS was examined by scratch test and ultrasonic bath experiment. The successive coated layers were studied by Raman spectroscopy, SEM-EDX, electron probe microanalysis and XPS. A special RPECVD reactor was designed to coat foams instead of plates. For the first time, a thin and homogeneous layer of silica could be deposited through the whole foam. The other steps were applied to obtain VOx/TiO2/SiO2/SS foams. XPS and Raman characteristics of deposits were the same than for coated plates and VOx/TiO2 powders.