Tuning the metal loading of Pt/CeO2 catalysts for the water-gas shift reaction
Clément Molinet‐Chinaglia, Luis Cardenas, P. Vernoux, L. Piccolo, S. Loridant
Abstract
Identifying active platinum species at the surface of Pt/CeO 2 catalysts is still a hot topic in the literature. In this work, an oxidizing pretreatment at 500 °C was applied to generate ultradispersed PtO x species before the reaction. It is shown that the molar activity of such catalysts for the water-gas shift reaction is strongly dependent on the platinum content, increasing by a factor of 2.5 from 0.1 to 0.6 wt% and stabilizing from 0.6 to 1.4 wt%. The tracking of Pt species present under reaction conditions (230 °C, H 2 O/CO=4) was performed using operando DRIFT spectroscopy, CO-TPR and STEM in connection with the catalytic activity. A major structural change was found for Pt loadings above 0.6 wt% through the formation of metallic Pt 0 nanoparticles of ca 1.4 nm from oxidized Pt single atoms and clusters. Conversely, for Pt contents below 0.6 wt%, Pt species possess a stronger interaction with CeO 2 as well as a lower nuclearity, limiting their activation under reaction conditions. This strongly suggests that metallic Pt nanoparticles, prevalent at high loading, are more active than oxidic Pt single atoms and small clusters, which are predominantly present at low loading. This study highlights the key role of PtO x reducibility and the importance to optimize the Pt loading to obtain active catalysts for the water-gas shift reaction. • Ultradispersed PtO x species supported on CeO 2 were evaluated for the WGS reaction. • The Pt molar activity increases from 0.1 to 0.6 wt% of Pt by a factor of 2.5. • Pt 0 nanoparticles are more active than PtO x single atoms and small clusters. • the Pt-molar activity is rather constant from 0.6 to 1.7 wt% of Pt. • This plateau arises from an increase in the number of Pt 0 nanoparticles without sintering.