Pt/CeO2 Catalysts for Low-Temperature CO Oxidation: Elusive Role of Ionic Pt
8th World Congress on Oxidation Catalysis
03-08 Sep 2017
|| Boronin Andrei Ivanovich
, Stadnichenko Andrey Ivanovich
, Slavinskaya Elena Markovna
, Kardash Tatyana Yurievna
, Muravev Valery V.
, Figueroba Alberto
, Bruix Albert
, Neyman Konstantin M.
Boreskov Institute of Catalysis SB RAS
Novosibirsk State University
University of Barcelona
Catalan Institution for Research and Advanced Studies
We discuss Pt loading and redox treatments as the main factors determining activity of Pt/CeO2 catalysts in CO oxidation at very low temperature. We found the Pt/CeO2 catalysts with low Pt loading to be inactive after pretreatment in O2 and activated after pretreatment in H2. Interestingly, the catalysts with high Pt loading show, after treatment in O2, extremely high activity already at temperatures below 0oC.
Using structural (XRD, TEM), spectral (XPS), kinetic (TPR-CO) and theoreti¬cal (DFT) methods we assigned such peculiar catalytic behavior to the pre¬sence of cationic Pt in ceria particles. Pt4f spectra (Fig. 1b,d) show that Pt2+ and Pt4+ ions are stabilized in ceria.
DFT calculations revealed strong distortions of the ceria fluorite lattice structure induced by Pt4+ and Pt2+ species, which facilitate – especially in nanoparticle models – generating large amount of very mobile lattice oxygen. Delivery of the latter for its reaction with CO can be mediated by surface metallic Pt or oxide PtOx clusters. Pretreatment in H2 causes a partial outlet of the ionic Pt to the surface with formation of Pt clusters, which accelerate CO oxidation starting at 0oC (Fig. 1a,c). Noteworthily, the strong growth of activity is coupled with the oxidation of surface Pt clusters to PtOx, which are thus identified as the actual active catalytic centers. Both surface PtOx and bulk Pt2+/Pt4+/CeO2 species are instantly formed upon pretreatment with O2 in the catalysts with high Pt loading. We measured a remarkably high activity for these catalysts at temperatures even lower than 0oC. Thus, ceria particles with incorporated ionic Pt and surface PtOx species appear to be a key combination to effectively catalyze CO oxidation at very low temperature.
Acknowledgements: This work was conducted within the framework of budget project No. 0303-2016-0003 for Boreskov Institute of Catalysis.