Hybrid catalysts for the selective catalytic reduction (SCR) of NO by NH3. On the role of fast SCR in the reaction network

Abstract

The SCR of NO by NH3 was studied with hybrid catalysts, in which an oxidation component (Mn-Cu or Ce-Zr mixed oxides) and SCR catalysts of different activities in fast SCR (Fe-ZSM-5 of different Fe content and H-ZSM-5) are combined in physical mixtures. Fast SCR, which is SCR of NO2/NO mixtures, is believed to be the final step of the reaction mechanism causing the synergy and being initiated by NO2 formation over the oxidation component. In our studies, no correlation between fast-SCR activity of the SCR component and the performance of the hybrid was observed. In addition, a hybrid catalyst was found that provided rates of standard SCR significantly exceeding rates in fast SCR achieved by the SCR component alone in a wide temperature range. Therefore, fast SCR is not part of the reaction sequence causing the drastic synergetic effects between the components.