Insight into the Synergic Effect of Fe-SSZ-13 Zeolite and FeMnTiZrOx Catalyst with Enhanced Reactivity in NH3-SCR of NOx

The relatively low activity at low temperatures and poor performance at high temperatures with low N-2 selectivity are the major problems of Fe-SSZ-13 zeolite and Mn-based metal oxides for NH3 selective catalytic reduction (SCR) of NOx, respectively. Hybrid catalysts have been prepared by mechanically mixing Fe(1.6)-SSZ-13 zeolite and Fe0.2Mn0.4TiZr0.03Ox to remedy the defects of both catalysts. The optimized mass ratio of zeolite and metal oxide components in hybrid catalysts is 7:1, which shows superior NH3 SCR performances with NO conversion above 80% and N2O yield below 12 ppm at wide-temperature window ranging from 200 to 550 degrees C. NO-TPD and in situ DRIFTS studies indicate that the metal oxide component in hybrid catalyst can provide more active nitrite/nitrate species as well as more active sites for NH3 activation to promote low-temperature activity. The migration of active intermediate from NO on the metal oxide component to react with NH3 adsorbed on zeolite component may be responsible for the enhancement of low-temperature activity. Strong adsorption of NH3 on zeolite component during SCR reaction can hinder NH3 oxidation, so high NO conversions and N-2 selectivity at high temperatures are maintained for hybrid catalyst. These insightful understandings on the synergic effect may be beneficial to rational design of high-performance hybrid catalysts in NH3-SCR reaction.