Deceleration of SO2 poisoning on PtPd/Al2O3 catalyst during complete methane oxidation

The inhibiting effect of SO2 on the catalytic activity of the monometallic Pt/Al2O3 and Pd/Al2O3, as well as on bimetallic PtPd/Al2O3 catalyst for the complete oxidation of methane under lean conditions has been studied. Flow reactor experiments, in-situ DRIFT spectroscopy and characterization with XPS, STEM-EDX were performed. It was found that the addition of Pt to the Pd/Al2O3 resulted in a catalyst that was more robust towards sulfur poisoning. XPS results revealed residual sulfates on catalyst surface after regeneration. This was confirmed with EDX analysis, which demonstrated that sulfur was accumulated in noble metal particles and especially in the region of the particle rich in Pt. Although the catalyst has been deactivated in the presence of both SO2 and H2O, an additional presence of NO in the gas mixture of reactants resulted in an increased lifetime of the sample under reaction conditions. This NO effect strongly depends on the temperature of experiments and is most intense at a temperature close to 550 degrees C A postponed inhibition caused by the addition of NO may be explained by the DRIFTS results, which demonstrated that the presence of NO lowers the sulfate formation and mostly surface sulfites are observed that increase the lifetime of the catalyst during SO2 exposure.