Hybrid catalysts with enhanced C₃H₆ resistance for NH₃-SCR of NO_x

Utilization of Fe-Beta for NH₃-SCR of NO_x in diesel engine applications is severely limited by hydrocarbon poisoning. In this work, a series of hybrid catalysts are prepared by mechanical mixing of zeolites and oxides, and their activity for the selective catalytic reduction of NO_x with NH₃ is investigated in the presence of propene. Results have shown that a catalyst prepared by mixing Fe-Beta and MnO_x/CeO₂ in a mass ratio of 1:1 exhibits high SCR activity. NO_x conversion in the temperature range 200–400 °C has exceeded 90% at a GHSV of 80,000 h⁻¹, with low selectivity to N₂O. By the combined DRIFTS and MS measurements, the function of MnO_x/CeO₂ in the hybrid catalysts is discussed. This hybrid catalyst is able to convert C₃H₆ to intermediates containing C[dbnd]O and COO functionalities, thereby decreasing carbon deposition on the zeolite and reduce the competitive adsorption between C₃H₆ and NO_x. Moreover, these intermediates react with NO_x at lower temperatures than do the carbonaceous deposits on Fe-Beta, enhancing the NO_x reduction activity.