On the reducibility of sulfated Pt/CeXZr1−XO2 solids: A coupled thermogravimetric FT-IR study using CO as the reducing agent

The reducibility of sulfate species by CO was studied over ceria and Ce0.63Zr0.37O2 mixed oxide with or without platinum, using infrared spectroscopy and thermogravimetry. The mechanism for sulfate reduction appeared to be based on three main points. Firstly, the exchange between surface and bulk-like sulfate species is required. The sulfate reduction indeed occurs at the oxide surface and bulk-like species need to migrate toward the surface to be further reduced. Secondly, it was observed that surface sulfate species are more easily reduced by CO on the reduced oxide. Therefore, platinum loading which favors the oxide reduction, also favors the sulfate reduction by CO. Finally, the reduction of sulfated Pt-free samples occurs in only one step, which is linked to the own reducibility of the surface sulfate species, probably through a direct interaction with CO. The amount of sulfur stored from sulfate reduction with CO is markedly more important than the one detected from reduction with H2. Furthermore, the oxygen storage capacity (OSC) for sulfated samples is higher than the one for sulfate-free samples. This is tentatively explained by the partial replacement of oxygen by sulfur atoms in the compound lattice.

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► We propose a mechanism for sulfate reduction by CO over ceria–zirconia oxides using FTIR and ATG.
► The mechanism involves a migration step between bulk-like and surface sulfate species.
► The platinum promoting effect would be directly linked with the better oxide reducibility.
► The oxide reduction is always concomitant to the sulfates one.
► The higher OSC of sulfated Ce-based catalyst is due to the replacement of some oxygen by sulfur atoms.