The
existence of different carbonaceous deposits on the catalysts
is well illustrated by the TPR spectra in Fig. 4. Nearly
the same features were found in all other cases. On Rh
containing samples a small portion of surface carbon was
hydrogenated to methane at 400–550 K and this was followed
by a high temperature peak above 600 K. Similar
TPR curves were found when the surface carbon was
produced in the decomposition of methane at 523 K and
only the ratio of the two peaks were different [43]. The low
and the high temperature TPR peaks were found in the
same temperature range irrespective of the metal or the
support. It means that the reactivity of these species
depends mainly on the composition and the structure of the
carbonaceous deposit.