A highly sulfur resistant Pt-Rh/TiO2/Al2O3 storage catalyst for NOx reduction under lean-rich cycles

Pt-Rh/TiO2/Al2O3 was investigated as a NOx storage-reduction catalyst using lean-rich cycles. It was found to be highly effective for NOx reduction and highly resistant to SO2 and H2O. In the presence of 100 ppm SO2 and 2.3% H2O, approximately 90% of NOx conversion was obtained at 250°C and a GHSV of 30,000 h−1 after 5 h lean-rich cyclic runs. A model NOx trap catalyst, Pt-Rh/BaO/Al2O3, was used for comparison. In the absence of SO2 and H2O, nearly complete removal of NOx was achieved. NOx conversion dropped to only 30% after SO2/H2O were introduced into the reactant gases at 300°C. With Pt-Rh/TiO2/Al2O3, over 70% NO conversion was still obtained at 400°C. Although, the BaO containing catalyst has much higher capacity for NOx than that containing TiO2, it is much more susceptible to SOx poisoning. In situ FT-IR spectra of the titania catalyst showed that nitrate species was the final adspecies (i.e. at the end of the lean phase) on the storage catalyst and its intensity was only slightly weakened in the presence of SO2 and H2O.