Rate assessments in the kinetic controlled regime, micro-kinetic modelling, CO and O2 chemical titration studies, together with density functional theory calculations lead to a mechanistic description for CO oxidation on dispersed Ag or Pt clusters on high surface area metal oxide substrates. Catalytic CO oxidation occurs via different reaction paths, depending on the metal ensemble size and the metal-support interactions, as these factors dictate the relative binding strengths of CO and oxygen on the catalyst sites, the ability to dissociate oxygen and generate the different reactive species (as lattice oxygen or molecular oxygen), and in turn, the kinetic dependences. On Ag cluster surfaces, which bind to CO* much more weakly than Pt clusters, both O* and CO* competitively adsorb on the clusters with the relative coverages determined by the operating [O2]-to-[CO]2 ratio. At low [O2]-to-[CO]2 ratios, Ag cluster surfaces saturated with CO* and as this ratio increases the clusters become saturated with O*. On Ag clusters, CO turnovers occur via kinetically relevant O2* and CO* reactions. For the contradictory case of Pt, which binds to CO* much more strongly, the reactions occur most effectively at a much lower barrier on dispersed Pt atoms on reducible metal oxide supports. These supports modify the charge of the Pt atoms and tune their electron densities, together with a vicinal site on the support that activates the O2* species, the CO turnovers are most effective at near ambient conditions. We compare and contrast the mechanistic requirements on the metal and interpreting these requirements in terms of their relative binding strengths to CO* and O*.

Low temperature carbon monoxide oxidation on transition metal and metal oxide catalysts

2019 Spring National Meeting

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