The highly dispersed metal nanoparticle catalysts Pd/Al2O3 and Pd/CeO2/Al2O3 respond dynamically to changes in the reactive atmosphere during CO oxidation in a packed-bed reactor. A combination of IR spectroscopy of adsorbed CO and X-ray absorption spectroscopy at the Pd K-edge reveal that surface and sub-surface Pd atoms undergo non-simultaneous redox changes as the temperature increases. The temperatures required to trigger these changes depend on the inlet P(CO)/P(O2) ratio, as well as the presence of absence of CeO2. Under lean conditions (P(O2) >> P(CO)), a dramatic and abrupt enhancement in reactivity occurs simultaneous with formation of a surface oxide as the temperature of Pd/Al2O3 increases. In the absence of ceria, the surface oxide is barely observable under near-stoichiometric conditions (P(O2) ~ P(CO)), and the catalyst is less active over the entire temperature range, while the ceria-promoted catalyst is readily oxidized even at low temperature and is more active.

Operando characterization of supported Pd nanoparticles during CO oxidation

247th National Meeting (2014)

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