Exhaust-gas reforming using precious metal catalysts

Rh-only and Rh bimetallic catalysts have been screened for exhaust-gas reforming, under conditions that mimic the output of an autoignition gasoline engine. Propane has been used as a model fuel, with simulated exhaust-gas providing the co-reactants (O2 and H2O) needed to generate hydrogen. Based on oxygen-conversion as a measure of light-off, Pt–Rh on ceria–zirconia shows the highest activity. In the presence of SO2, adsorbed sulphur species do not inhibit the oxidation reactions that induce light-off, but suppress the major pathway to hydrogen (steam reforming). By excluding platinum and using silica-enriched alumina as the underlying support, light-off is delayed, but the steam reforming reaction becomes much more insensitive to the presence of sulphur. The Pt–Rh catalyst is most suited to exhaust-gas reforming systems in which the engine runs on a sulphur-free fuel, whereas the Rh-only catalyst is the better choice when the fuel is conventional gasoline.