Regeneration of S-poisoned Pd/Al2O3 catalysts for the combustion of methane

Regeneration of S-poisoned Pd/Al2O3 catalysts for the abatement of methane emissions from natural gas vehicles was addressed in this work. Investigations were devoted to determine the temperature threshold allowing for catalyst reactivation under different CH4 containing atmospheres. Under lean combustion conditions in the presence of excess O-2, partial regeneration took place only above 750 degrees C after decomposition of stable sulphate species adsorbed on the support. Short CH4-reducing, O-2-free pulses led to partial catalyst reactivation already at 550 degrees C and to practically complete regeneration at 600 degrees C. Also in this case reactivation was associated with SO2 release due to the decomposition of stable support sulphates likely promoted by CH4 activation onto the reduced metallic Pd surface. Rich combustion pulses with CH4/O-2 = 2 were equally effective to CH4-reducing pulses in catalyst regeneration. These results suggest that a regeneration strategy based on periodical natural gas pulses fed to the catalyst by a by-pass line might be efficient in limiting the effects of S-poisoning of palladium catalysts for the abatement of CH4 emissions from natural gas engine.