Abstract
Spatially- and component-resolved kinetic measurements and resulting phase diagrams for CO oxidation on a model catalyst consisting of Pd powder agglomerates supported by a polycrystalline Pt foil are reported. The kinetic data for the micrometer-sized Pt(100) and Pt(110) domains and for the different Pd powder ag- glomerates of similar dimensions were obtained by local analysis of PEEM video-sequences recorded in situ during the ongoing CO oxidation reaction. Individual domains of the supporting Pt foil as well as the lm-sized Pd powder agglomerates behave in the combined Pdpowder/Ptfoil sam- ple independently from each other with respect to CO oxidation, at least in the 10 -5 mbar pressure range. The propagating reaction fronts move within grain boundaries for Pt domains and also remain confined to the Pd agglomerates.
Highlights
Modern technical catalysts used e.g. in automotive catalytic converters are typically multicomponent systems consisting of mixed metal oxides and different supported precious metals, such as Pt, Pd, Rh [1,2,3]
Spatially- and component-resolved kinetic measurements and resulting phase diagrams for CO oxidation on a model catalyst consisting of Pd powder agglomerates supported by a polycrystalline Pt foil are reported
The kinetics of CO oxidation on a model system surface can be summarized by a so-called kinetic phase diagram, a chart in the T, pCO, pO2 parameter space, where the transition points between the steady states of high reactivity and low reactivity as well as the region of bistability are plotted [15, 16]
Summary
Modern technical catalysts used e.g. in automotive catalytic converters are typically multicomponent systems consisting of mixed metal oxides and different supported precious metals, such as Pt, Pd, Rh [1,2,3]. The problem of catalytic properties evaluation for spatially separated species on the same sample is in principle similar to that of individual domains of a heterogeneous surface This task was recently solved, at least for CO oxidation on Pt and Pd, by the ‘‘kinetics by imaging’’ approach employing photoemission electron microscopy. In the current contribution we extend this idea to lmsized Pd powder agglomerates supported by a polycrystalline Pt foil consisting of differently oriented domains (50–100 lm in size, Fig. 1b) Such a model system is well suitable for proving the possibility to study the reaction kinetics in a spatially-resolved and in a component-distinctive way since the parameter ranges of catalytic activity for CO oxidation differ significantly for Pd and Pt [8]. This allows an easy differentiation between the Pt support and Pd powder particles down to the resolution limit of the available PEEM (a few lm in our case)
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