The catalytic behavior of Rh particles supported by three
different
materials (Rh, Au, and ZrO2) in H2oxidation
has been studied in situ by correlative photoemission electron microscopy
(PEEM) and scanning photoemission electron microscopy (SPEM). Kinetic
transitions between the inactive and active steady states were monitored,
and self-sustaining oscillations on supported Rh particles were observed.
Catalytic performance differed depending on the support and Rh particle
size. Oscillations varied from particle size-independent (Rh/Rh) via
size-dependent (Rh/ZrO2) to fully inhibited (Rh/Au). For
Rh/Au, the formation of a surface alloy induced such effects, whereas
for Rh/ZrO2, the formation of substoichiometric Zr oxides
on the Rh surface, enhanced oxygen bonding, Rh-oxidation, and hydrogen
spillover onto the ZrO2support were held responsible.
The experimental observations were complemented by micro-kinetic simulations,
based on variations of hydrogen adsorption and oxygen binding. The
results demonstrate how correlative in situ surface microscopy enables
linking of the local structure, composition, and catalytic performance.