Fig. 9 shows C 1s XPS of all used catalysts which was conducted
to determine the type of carbon species formed during
steam reforming. Catalysts Ni/b, Pd/b and Ni-Pd/b (non-Rh) displayed
a large peak at 286.3 eV, attributed to a polymeric and/or
aromatic type of carbon species [26,33]. This peak also displayed a
broad tailing at the high binding energy end, normally attributed to
highly dehydrogenated species of carbon. Catalysts containing Rh
contained only a single peak at 284.7 eV, generally assigned to the
hydrocarbon and/or graphitic carbon, indicating that Rh inhibited
the formation of aromatic/polymeric type of carbon [34]. Since Ni/b,
Pd/b and Ni-Pd/b catalysts deactivated rapidly relative to the catalysts
containing Rh, it is likely that formation of aromatic/polymeric
carbon was a primary deactivation mechanism.