In many applications for exhaust gas aftertreatment, ammonia is added to the flue gas as a reducing agent for nitrogen oxide (NOx) emissions. An effective dosing control is necessary to avoid low NOx conversion or ammonia slip. The here-investigated capacitive zeolite-based sensor helps to monitor the concentration of ammonia in the flue gas. For the specific application of biomass combustion plants, preliminary sensor investigations have been carried out in the laboratory. Special emphasis was given on investigating cross-sensitivities that could be caused by the large number of other components in the flue gas. An impressing selectivity was found. By adjusting the composition of the zeolite functional film and the operating temperature, the remaining small influences of NOx and water vapor could be even further reduced. The described sensor concept should be an ideal solution for improving the NOx aftertreatment efficiency.
Wöhrl et al. (2025) studied this question.