Revealing the Dynamic Structure of Complex Solid Catalysts Using Modulated Excitation X-ray Diffraction
Résumé
X-ray diffraction (XRD) is typically silent towards information on low loadings of precious metals on solid catalysts because of their finely dispersed nature. When combined with a concentration modulation approach time-resolved high energy XRD is able to provide the detailed red-ox dynamics of Pd nano-particles of ca. 2 nm in 2 wt% Pd/CZ, an otherwise difficult sample for EXAFS because of the presence of Ce. The detailed temporal evolution of the Pd(111) and Ce(111) reflections together with surface information from synchronous DRIFTS measurements reveals that Ce maintains Pd oxidized during a 30 s CO pulse while reduction is detected at the beginning of the 30 s O2 pulse. Oxygen is likely transferred from Pd to Ce3+ before the onset of Pd re-oxidation. In this context, adsorbed carbonates appear to be the rate limiting species for re-oxidation.
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