Sensing Catalytic Conversion : Simultaneous DRIFT and Impedance Spectroscopy for in situ Monitoring of DeNOx-SCR on Zeolites

Title data

Simons, Thomas ; Chen, Peirong ; Rauch, Dieter ; Moos, Ralf ; Simon, Ulrich:
Sensing Catalytic Conversion : Simultaneous DRIFT and Impedance Spectroscopy for in situ Monitoring of DeNOx-SCR on Zeolites.
In: Sensors and Actuators B: Chemical. Vol. 224 (1 March 2016) . - pp. 492-499.
ISSN 0925-4005
DOI: https://doi.org/10.1016/j.snb.2015.10.069

Project information

Abstract in another language

In order to meet the legislative emission requirements for NOₓ-containing exhaust gases, SCR catalysts, in particular zeolites, are used. To improve catalysts and the catalytic processes, an in-depth understanding of the reaction mechanisms is required as well as an analysis of the physicochemical properties of the SCR catalysts, preferably in real-time. Here, we introduce a setup combining impedance spectroscopy and infrared spectroscopy in diffuse reflection mode for in situ measurements on zeolites under SCR-related conditions. This setup allows for the first time to simultaneously monitor both, the proton conductivity of zeolites and the vibration modes of the molecules involved in the catalytic conversion of NO by NH₃. We studied both, pure and Fe-promoted H-form zeolites, as sensors and model catalysts at the same time, and found out that weakly bound NH₃ is dominating the proton conductivity of both zeolites in a temperature range below the desorption temperature of NH₃. When a part of the weakly bound NH₃ is consumed by the SCR reaction, proton conductivity and thus the sensing effect gets dominated by strongly bound NH₃. This allows applying impedance spectroscopy to assess the degree of NH₃ loading and the state of the SCR conversion process in zeolite catalyst.