Methane catalytic combustion over Pd/Al2O3 in presence of sulphur dioxide: development of a deactivation model Original Research Article

The effect of the concentration of sulphur dioxide (in the range 15–65 ppm) and temperature (350–550 °C) on the deactivation of a commercial Pd/Al2O3 catalyst used in the oxidation of methane has been studied. It was observed that, although at a given temperature a common steady-state of constant methane conversion was attained for all sulphur dioxide concentrations, the deactivation rate increased as sulphur dioxide concentration in the feed increased. On the other hand, the deactivation rate decreased as temperature increased the activity at steady state increasing as temperature increased. The behaviour of the system has been modelled considering that the methane combustion follows a pseudo-first-order with respect to methane kinetics, whereas the deactivation is caused by the formation of surface Pd sulphate, which is less active than Pd oxide. The rate of formation of Pd sulphate is considered to be first-order for both sulphur concentration and fraction of unsulphated Pd. The proposed deactivation model, in addition to being in good agreement with the deactivation mechanisms proposed in the literature for this process, provides a good fit for the experimental results for which the deactivation may be assumed to be caused by sulphur poisoning only.