Influence of redox treatments on the low-temperature water gas shift reaction over Pt/CeO2 catalysts†

Abstract

Pt/CeO₂ catalysts are promising for the low-temperature water gas shift (LT-WGS) reaction, which is an important step to produce H₂ from syngas. When prepared by impregnation of platinum salt and calcination at 500 °C, they contain Pt²⁺ single atoms (SAs) and/or PtO_x clusters which need to be converted into Pt⁰ nanoparticles (NPs) to obtain higher activity for the LT-WGS reaction. In this work, it was shown that reducing pretreatments at 250 °C under H₂ promote the molar activity of catalysts containing from 0.10 to 1.06 wt% Pt by increasing the number of Pt⁰ NPs formed during reaction at 230 °C. An improvement was also obtained via pretreatment at 500 °C but only for low-Pt-content catalysts, underlying the importance of the pretreatment temperature. Furthermore, it was shown that all prepared Pt/CeO₂ catalysts which slowly deactivate over reaction time can be regenerated by oxidative post-treatment at only 230 °C, which is industrially interesting. Even more original, a strong improvement in activity of the low-Pt-content catalysts was observed after a 12 h oxidative post-treatment at 500 °C. This treatment was shown to redisperse and reoxidize Pt atoms into PtO_x species different from the initial ones. Such species are highly reducible on the surface of CeO₂ and easily transformed into active Pt⁰ NPs.