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 NO x 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 NO x reduction activity with isooctane as the reducing agent. A maximum NO x 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 NO 2 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 NO 2 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 NO x reduction with propene occurred primarily in the extrudate containing ferrierite. Again, the selectivity of NO 2 to form nitrogen governed the overall NO x reduction.