In Situ Redispersion of Platinum Autoexhaust Catalysts: An On‐Line Approach to Increasing Catalyst Lifetimes?

Abstract

Dynamic observation: The rapid oxidative redispersion of large Pt nanoparticles supported on ceria‐based oxide in autoexhaust catalysts is demonstrated in the absence of Cl by in situ XANES analysis. An atomic migration model accounts for the observed redispersion through the trapping of Pt species at sites on the Ce support that exhibit strong interactions between the Pt oxide and the support.

Time Resolved Operando X-ray Techniques in Catalysis, a Case Study: CO Oxidation by O2 over Pt Surfaces and Alumina Supported Pt Catalysts

“…Two reactive (more reactive so than the metallic surface) surface oxides where therefore shown to be formed over Pt (110) at elevated pressure, and net oxidizing conditions. Two reactive (more reactive so than the metallic surface) surface oxides where therefore shown to be formed over Pt (110) at elevated pressure, and net oxidizing conditions.…”

“…Two reactive (more reactive so than the metallic surface) surface oxides where therefore shown to be formed over Pt (110) at elevated pressure, and net oxidizing conditions. The commensurate oxide only forms in the presence of significant amounts (though not too much) of CO and is eventually replaced by the incommensurate PtO2 surface oxide when the CO/O2 ratio diminishes to below ca.…”

“…The Pt L3-edge during these experiments shows two subtle, but measurable, changes during these transient experiments: variation in the intensity of the Pt L3-edge white line and the energetic position of the edge itself (0.6 eV at most). The overall shape of the Pt XANES is undeniably metallic and these changes are indicative, within certain approximations-as the detailed structure of the Pt L3-edge XANES can also be indicative of changes in size [108][109][110], or indeed morphology [111]-of the oxidation of the surfaces of nanoparticles during the switch from a new reducing (CO) to net oxidizing (O2) environment.…”

“…(a) The surface oxides (incommensurate and commensurate) identified by Ackermann et al [116] to be to present during elevated pressure CO oxidation over Pt (110) using operando SXRD in the apparatus shown in Figure 4 and in both real and reciprocal space. The commensurate oxide only forms in the presence of significant amounts (though not too much) of CO and is eventually replaced by the incommensurate PtO 2 surface oxide when the CO/O 2 ratio diminishes to below ca.…”

“…Some exemplary results, highlighting aspects of this method, are shown in Figures 8 and 9 from the study of Butcher et al [134] regarding CO oxidation at elevated pressures on Pt (110). XPS also brings with it an intrinsic level of surface sensitivity-due to the underlying physics of electron atom interactions that also plays a part in making EXAFS an intrinsically short range probe of local bulk structure-that is not intrinsic to XRD and XAFS as a result of energy of the X-rays, be they incident or fluorescent, applied or detected, generally used in the latter two methods.…”