Effect of metal foam supports on the selective oxidation of CO on Fe-promoted Pt/γ-Al2O3

Fe promotion is known to significantly increase the activity of Pt catalysts for the selective oxidation of CO in H2 for fuel cell applications. Use of metal foams as catalyst structural supports in catalytic reactors can improve reactor characteristics by lowering the pressure drop and increasing heat transfer. In a previous study on metal foam-supported Pt catalysts, it was shown that Cr and Fe impurities from the metal foam were present in significant quantities in the washcoat, improving the catalytic properties of the catalysts. This study addressed the effect that these Cr and Fe impurities may have on metal foam supported PtFe (5 wt.% Pt, 0.5 wt.% Fe based on the loading of alumina washcoat) catalysts. Foam-based PtFe catalysts with different numbers of pores-per-inch (30-50) and percentage relative metal densities were 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 PtFe catalyst (also 5 wt.% Pt and 0.5 wt.% Fe) and foam-based Pt catalysts. The foam-based PtFe catalysts exhibited reaction properties similar to those of the powdered PtFe/γ-Al2O3 catalyst. The intrinsic site activities of all foam-based PtFe catalysts determined using isotopic transient kinetic analysis (ITKA) were approximately the same and seemed to be characteristic of Fe-promoted Pt/γ-Al2O3. Thus, the presence of Cr and Fe impurities in the washcoat from the metal foam does not seem to have a major impact on reaction on Fe-promoted Pt even though it appears to significantly affect both H2 and CO chemisorption at 37 °C. This was not the case for the comparison previously of foam-based and powdered Pt/γ-Al2O3 catalysts. These foam-based PtFe catalysts exhibited only a slight change with time-on-stream of CO oxidation rate and % CO2 selectivity and did not show the rapid initial deactivation to steady state, typically seen for both γ-Al2O3-supported Pt and PtFe catalysts. This initial stable activity and selectivity is preferable for commercial use.