Study of sulfur poisoning on Pd/Al2O3 and Pd/CeO2/Al2O3 methane combustion catalysts

In the present work the CH4 combustion behavior of Pd/Al2O3 and Pd/CeO2/Al2O3 catalysts in the presence of SO2 is investigated under various reaction conditions. Attention is paid also to the behavior of the bare supports without the active phase. Both fresh and poisoned samples are characterized by IR spectroscopy and in situ CO adsorption. Transient activity measurements after SO2 poisoning indicate that regardless of CeO2 loading a strong deactivation of all catalysts is observed compared to fresh samples. The effect of sulfur poisoning on steady state activity at 653 and 873 K is also measured. The deactivation is evident only at 653 K and its dynamics reflects the dynamics of SO2 adsorption. Results of TPD experiments under inert or reaction atmosphere suggest that the dynamics of SO2 desorption is influenced by the combustion reaction taking place on the catalyst active sites. Ceria-doped catalysts are more sensitive to the composition of the atmosphere of adsorption/desorption and quantitative measurements indicate that the presence of CeO2 inhibits SO2 adsorption under reaction conditions.