Preparation and Electrochemical Characterization of Noble metal modified Fe-Cr-Al Alloy Foam Catalysts for High-Temperature Oxidation Reactions

Foams of Fe-Cr-Al alloys, currently called Fecralloy, with typical composition close to 22 wt% Cr, 5 wt% Al and Fe balance, are extensively used as large-area supports for catalytic nanoparticles in high temperature applications, like catalytic combustion or partial oxidation of methane, where extremely low pressure drops and outstanding resistance to oxidative degradation are mandatory. We have explored both spontaneous deposition and electrodeposition of noble metals (M = Pd, Pt or Rh) onto Fecralloy foams as alternative routes for the preparation of M-Fecralloy catalysts, which are significantly simpler than the currently employed washcoating methods. The as-prepared structured catalysts were characterized by SEM-EDS, XRD and electrochemical methods; then their catalytic activity was measured; finally they were characterized again. Cyclic voltammetry was employed to determine the real surface area of the noble metals both before and after their use in high-temperature oxidation tests. The figure compares the voltammograms recorded with an as-prepared and a used Pd-Fecralloy catalyst with equal Pd loadings (LPd). An unexpected marked increase in the reduction charge of the Pd surface oxides to Pd (peak at -210±5 mV vs. Hg|HgO), assumed to be proportional to the Pd surface area, was observed after prolonged use of Pd-Fecralloy foams in the catalytic oxidation of methane and CO. Acknowledgments: The authors acknowledge the financial support of the Italian Ministry for Economic Development (MSE) - MSE-CNR Agreement on National Electrical System.