The Effect of Copper Loading on the Selective Catalytic Reduction of Nitric Oxide by Ammonia Over Cu-SSZ-13
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The effect of Cu loading on the selective catalytic reduction of NOx by NH3 was examined over a series of Cu ion-exchanged (20–80%) SSZ-13 zeolite catalysts. High NO reduction efficiencies (80–95%) were obtained over all catalyst samples between 250 and 500 °C, and at the gas hourly space velocity of 200,000 h−1. Both NO reduction and NH3 oxidation activities under these conditions were found to increase slightly with increasing Cu loading at low temperatures. However, NO reduction activity was suppressed with increasing Cu loadings at high temperatures (>500 °C) due to excess NH3 oxidation. The optimum Cu ion exchange level appears to be ~40–60% since higher than 80% NO reduction efficiency was obtained over 50% Cu ion-exchanged SSZ-13 up to 600 °C. The NO oxidation activity of Cu-SSZ-13 was found to be low regardless of Cu loading, although it was somewhat improved with increasing Cu ion exchange level at high temperatures. During the “fast” SCR (i.e., NO/NO2 = 1), only a slight improvement in NOx reduction activity was obtained for Cu-SSZ-13. Regardless of Cu loading, near 100% selectivity to N2 was observed; only a very small amount of N2O was produced even in the presence of NO2. The apparent activation energies for NO oxidation and NO SCR were estimated to be ~58 and ~41 kJ/mol, respectively.