Lean hydrocarbon selective catalytic reduction over dual pore system zeolite mixtures

Physical mixtures of CuFER and HZSM-5, CuFER and AgMOR, and CoFER and AgMOR zeolites were investigated as potential dual pore system catalysts for continuous lean NOx reduction with propene or isooctane as reducing agents. The effects of variations in temperature and oxygen concentrations were studied using steady-state experiments. Despite lower rates of external and internal mass transfer, the mixture of CuFER and HZSM-5 was found to have the highest NOx reduction activity with isooctane as the reducing agent. A maximum NOx reduction of about 40% was found for this catalyst at 350 °C and 12% oxygen. In this case, the CuFER extrudate acted as an NO oxidation catalyst, and the NO2 formed was reduced by the isooctane in the HZSM-5 extrudate. The better performance of the CuFER and HZSM-5 mixture compared with the other mixtures was attributed to a higher selectivity for NO2 to form nitrogen in the reduction reaction. When propene was used, the two mixtures containing CuFER showed similar reduction activity with a maximum conversion of about 65% at 370 °C and 2% oxygen. In contrast with the isooctane, the NOx reduction with propene occurred primarily in the extrudate containing ferrierite. Again, the selectivity of NO2 to form nitrogen governed the overall NOx reduction.