In situ monitoring of DeNOx-SCR on zeolite catalysts by means of simultaneous impedance and DRIFT spectroscopy

Abstract

The development of more efficient zeolite catalyst for selective catalytic reduction of NOx (DeNOx-SCR) requires the analysis of the real-time state of the catalyst (e.g. NH3 storage level) and the reaction mechanism. Impedance spectroscopy (IS) allows to electrically sense the uptake of NH3 into proton conducting catalysts. By means of IS we reveal that Cu-SAPO possesses higher response to NH3 than Cu-ZSM-5 over a broad temperature range from 80°C to 450°C. IS can thus be used to determine the NH3 storage and to monitor the SCR reaction in situ. Simultaneous IS and DRIFTS study under in situ conditions unveiled that the proton conductivity of Cu-SAPO is related to the ammonium nitrate intermediate, NH3 species bounded to both Cu sites and Brønsted acid sites. However, the contribution of each species to the conductivity varied in different reaction conditions. This correlation of integral electrical response with molecular processes paves a new route for the in situ monitoring and mechanistic understanding of zeolite-catalyzed SCR reactions.