Use of catalytic oxidation and dehydrogenation of hydrocarbons reactions to highlight improvement of heat transfer in catalytic metallic foams

Abstract

Two model reactions were used to show the influence of catalytic foams on improving heat transfer. The catalytic performances were compared to those observed when using the same reactors packed with catalytic powder or beads. One reaction was the exothermic oxidative dehydrogenation of propane which was investigated on 7%V 2O 5/TiO 2 coated on stainless steel foam. A silica layer was first deposited on the foam surface by Remote Plasma Enhanced Chemical Vapour Deposition to avoid poisoning of active phase by iron species, to favour the anchoring of TiO 2 support and to accommodate the difference of dilatation coefficients. When comparing catalytic foams with powders in the same reactor, the selectivity to propene at isoconversion was higher by 12–45 mol% for the same amount and composition (7%V 2O 5/TiO 2) of the active phase and in the same operating conditions (contact time, C 3/O 2 ratio, temperature range). The other reaction was the endothermic dehydrogenation of methylcyclohexane on 2%Pt/Al 2O 3 directly coated on foams and on molecular sieve beads. To study the influence of heat and mass transfers, the material (FeCrAlloy or alumina) and porosity (81–97%) of foams were varied. It was found that, even for highly exothermic or endothermic reactions not limited by external transport, the coated foams significantly increased the effective conductivity of catalytic beds, the denser foam leading to higher effective conductivity.