科研之友
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摘要
Manganese oxide supported palygorskite (MnOx/PG) catalysts are considered highly efficient for lower-temperature selective catalytic reduction (SCR) of flue gas NO by ammonia. However, during the SCR reaction, the surface of the MnOx/PG catalyst tends to get poisoned by SO2. In this study, we have doped the MnOx/PG catalyst with cerium oxide to improve their resistance against SO2 poisoning. The SCR activity of the CeO2-doped catalyst (Mn-Ce/PG) is found to be remarkably higher than that of the undoped MnOx/PG catalyst in the temperature range of 100-200 degrees C in the presence of 400 ppm SO2. Of all the different samples with different concentrations of Ce doping, the catalyst Mn8Ce5/PG exhibits the highest SCR activity in the presence of SO2-containing gases. Systematic analyses of the sample performed by using XRD, XPS, SEM-EDS, temperature programmed desorption (TPD) and TGA suggest that the cerium oxide doping can obviously inhibit the SO2-poisoning of the active species manganese oxides, which is widely believed to be one of the major reasons for the deactivation of manganese-based catalysts. However, the deposition of ammonium sulfates on the surface of catalysts, which is yet another important cause of SO2 poisoning, can hardly be avoided via the addition of cerium oxide. On the basis of systematic studies, it can be assumed that the addition of cerium oxide can enhance the stability of the active species via the reduction of manganese sulfate rather than ammonium sulfates, thereby improving its resistance toward SO2 poisoning.
