hide
Free keywords:
rhodium black, platinum black, surface carbon, surface oxygen, methylcyclopentane
carbon deposit on Rh and Pt catalysts
Abstract:
The surface composition of Rh and Pt blacks (as determined by XPS) shows carbon and oxygen impurities in the untreated state. Oxygen on Pt is present as
adsorbed O as well as OH/H2O groups and oxidized carbon. Rh was partly oxidized to Rh2O3, in agreement with UPS showing hardly any Fermi-edge intensity
in untreated Rh as opposed to untreated Pt. High Fermi-edge intensities indicated a predominant metallic surface after an in situ treatment with H-2 at 483 K,
increasing the purity (XPS) to similar to 90%. This treatment reduced Rh to metal and removed its C impurity. Pt, in turn, retained much carbon after H-2
treatment, present mainly as graphitic carbon. A minor amount of CO was also detected, some of the O 1s peak belonging to it. The two metals were tested in
methylcyclopentane reactions. Considering the necessity of carbon for nondegradative reactions and oxygen enhancing fragmentation, a correlation is suggested
between the typical impurities of Pt and Rh and their respective catalytic propensities: the high fragmentation activity of Rh and the predominant nondegradative
reactions to C-6 "ring opening products" on
