N. Savargaonkar et al., INFLUENCE OF HYDROGEN CHEMISORPTION ON THE SURFACE-COMPOSITION OF PT-RH AL2O3 CATALYSTS/, Journal of catalysis, 162(2), 1996, pp. 277-283
The surface compositions of a series of platinum-rhodium bimetallic ca
talysts supported on gamma-alumina were determined in the presence of
chemisorbed hydrogen by H-1 NMR spectroscopy. The surface compositions
of hydrogen-covered Pt-Rh bimetallic catalysts were found to be sligh
tly enriched in Rh, significantly different from the surface compositi
ons of adsorbate-free Pt-Ph surfaces, which are enriched in Pt. Furthe
r, based on selective excitation NMR experiments it was found that bim
etallic particles of fairly uniform compositions were formed. Atomisti
c simulations of hydrogen-covered Pt-Rh bimetallic catalysts were done
using a method that involved coordination-dependent bond energies. Th
e simulations indicated that the heat of adsorption of hydrogen on rho
dium is about 13 kJ/mol higher than that on platinum. Finally, a gener
al, qualitative method for predicting the influence of adsorbates on t
he surface segregation behavior of bimetallic systems is described on
the basis of knowledge of the surface energies at various sites and th
e heats of adsorption. (C) 1996 Academic Press, Inc.