NOx adsorption and reduction with C3H6 over Fe/zeolite catalysts: Effect of catalyst support

The effect of catalyst supports on NOx adsorption and reduction by C3H6 over Fe/zeolites was studied at a temperature range of 200-400 °C. NOx conversion over Fe/zeolites decreased in the order of Fe/MOR > Fe/FER ≈ Fe/ZSM-5 > Fe/Beta at low temperatures between 200 °C and 300 °C. At temperatures above 300 °C, the order of catalytic activity became Fe/Beta > Fe/FER > Fe/ZSM-5 > Fe/MOR. NOx adsorption capacities on Fe/zeolite catalysts decreased in the order of Fe/MOR > Fe/FER > Fe/ZSM-5 > Fe/Beta. The selective catalytic reduction (SCR) activity of zeolites showed a slight difference from 200 °C to 400 °C. The adsorption capacities of NO on zeolites placed within the rank of MOR > FER > ZSM-5 > Beta. No correlation was found between surface area/pore volume and NOx reduction/adsorption on Fe/zeolites. The ratio of Fe2+/Fe3+ in the surface layer of Fe/zeolites decreased in the order of Fe/Beta > Fe/FER > Fe/MOR > Fe/ZSM-5. The peak of Fe3O4 was clearly detected on Fe/Beta by TPR. The inhibition of the adsorption capacities of Fe/zeolites became severe in the presence of SO2, CO2, and H2O. CO2 exerted virtually no effect on the SCR activity of Fe/zeolites. The inhibition of NOx conversion by H2O was reversible for all catalysts. NOx conversion dropped significantly on Fe/zeolites in the presence of 100 ppm SO2, 10% H2O, and 10% CO2. The Fe/MOR catalyst exhibited the strongest tolerance to SO2 among tested catalysts, showing its promise as a practical catalyst for lean-burn de-NOx in an internal circulating fluidized bed in the presence of low sulfur levels in exhaust gases.