Insight into the Synergic Effect of Fe-SSZ-13 Zeolite and FeMnTiZrO_<i>x</i> Catalyst with Enhanced Reactivity in NH₃–SCR of NO_<i>x</i>

Abstract

The relatively low activity at low temperatures and poor performance at high temperatures with low N2 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 °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 N2 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