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

Abstract

Abstract VO x /TiO 2 , catalyst of oxidative dehydrogenation of propane, was immobilised on a SiO 2 film coating stainless-steel (SS) plates and foams figuring out structured reactors. SiO 2 is expected to act as a primer and a barrier against poisoning of VO x /TiO 2 catalyst by elements of SS. The adhesive SiO 2 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 μm-thick tetramethyldi-siloxane polymer layer, followed by calcination (650 °C) to obtain the SiO 2 layer. A post-treatment in N 2 /1.5%O 2 plasma afterglow was necessary to eliminate remaining carbon traces after calcination. The resulting SiO 2 /SS objects were dip-coated in TiO 2 -anatase aqueous suspension. Vanadium isopropoxide was grafted on calcined TiO 2 /SiO 2 /SS, yielding VO x polyvanadates after calcination at 450 °C. The mechanical stability of the VO x /TiO 2 catalyst immobilized onto SiO 2 /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 VO x /TiO 2 /SiO 2 /SS foams. XPS and Raman characteristics of deposits were the same than for coated plates and VO x /TiO 2 powders.