A thermogravimetric and FT-IR study of the reduction by H2 of sulfated Pt/CexZr1−xO2 solids

The nature, concentration and reducibility by H2 of sulfate species formed from SO2 oxidation were studied over a range of Pt/CexZr1−xO2 catalysts using infrared spectroscopy and thermogravimetry. Ionic sulfates were formed over ceria and Ce-containing catalysts, even at high Zr content. The sample-specific surface area, the presence of platinum and the zirconium proportion affected the rate and extent of formation of sulfate in the bulk of the materials. Sulfate reduction by H2 first occurred at the CexZr1−xO2 surface. Bulk-like S-containing species subsequently migrated towards the surface to continuously replace surface sulfates removed by the reduction. The temperature required for sulfate migration as well as that necessary for sulfate reduction increased with the Zr content. The amount of stored sulfur is closely linked to the specific surface area of the sample. Finally, we have clearly shown that thermogravimetry was an appropriate technique for evaluating the oxygen storage capacity (OSC) of sulfated ceria–zirconia mixed oxides, despite the additional complexity due to the presence of sulfate compounds and various reduced S-species that can be formed during sample reduction.