Metal foam supported Pt catalysts for the selective oxidation of CO in hydrogen

Pt has been found to be an active catalyst for the selective oxidation of CO in H2 for fuel cell applications. Washcoated metal foam structures supporting such a catalyst offer interesting possibilities for commercial application due to low pressure drop, excellent flow characteristics through the foam, and excellent heat transfer properties. This study reports on the effects of using γ-Al2O3-washcoated metal foams (FeCrAlY) as structural supports for 5 wt.% Pt catalysts. Foam-based catalysts with different number of pores per inch (30-50) were prepared, characterized, investigated for their activities and surface kinetic parameters for the selective oxidation of CO in H2, and compared with a powdered γ-Al2O3-supported Pt catalyst of the same composition. The presence of Fe impurities in the washcoat, probably from the metal foam structure, was found to have a significant impact on the properties of the foam-based catalysts. The foam-based Pt catalysts exhibited reaction properties similar to those of Fe-promoted Pt/γ-Al2O3. Compared to the unpromoted powdered Pt catalyst, the metal foam supported Pt catalysts gave lower H2 and CO chemisorption, higher CO2 selectivity in selective oxidation, and higher pseudo-first-order rate constants based on isotopic tracing-all of which are characteristics of Fe promotion of Pt. Isotopic tracing results show that the number of active sites contributing to the reaction was the same for both types of catalysts. Although site blockage was the main cause for the initial deactivation of the powdered Pt catalyst, both a decrease in intrinsic activity and site blockage were the cause of a similar initial deactivation for the foam-based Pt catalysts. There was also a shift downward in the activity distribution determined by ITKA during the initial deactivation of the foam-based catalysts. These latter two effects are similar to what is seen when Pt/γ-Al2O3 is promoted with Fe. The results indicate that active Pt catalysts for the selective oxidation of CO in H2 can be prepared using washcoated metal foam structures.