Abstract
Sensors that detect directly and in situ the status of automotive exhaust gas catalysts by monitoring the electrical properties of the catalyst coating itself are overviewed. Examples included in this review are the in-situ determination of the electrical impedance of three-way catalysts based on ceria-zirconia solutions and of lean NOx traps of earth-alkaline based coatings, as well as approaches to determine the ammonia loading in Fe-SCR-zeolites with electrical ac measurements. Even more sophisticated approaches based on interactions with electromagnetic waves are also reviewed. For that purpose, metallic stick-like antennas are inserted into the exhaust pipe. The catalyst properties are measured in a contactless manner, directly indicating the catalyst status. The radio frequency probes gauge the oxygen loading degree of three-way catalysts, the NOx-loading of lean NOx traps, and the soot loading of Diesel particulate filters.
Highlights
In the past years, many efforts were being made to develop novel automotive exhaust gas sensors that are sensitive, selective, have long-term stability, and are cost effective
Overviewed examples include: o In-situ monitoring of the impedance of ceria-zirconia based three-way catalysts (TWC) to determine their degree of oxygen loading, o In-situ measurement of the impedance of earth-alkaline oxide-based lean NOx traps (LNT) coating materials to detect the status of an LNT with respect to its NOx-loading, its status of regeneration, its degree of sulfurization, and its thermal aging, o Approaches to determine the ammonia loading in Fe-SCR catalysts (SCR)-zeolites with electrical ac measurements
NOx removal technologies, NH3-SCR and LNT, novel exhaust gas sensors that provide information on the status of the catalyst to supplement the well-known and mature lambda probe would be helpful for catalyst control
Summary
Many efforts were being made to develop novel automotive exhaust gas sensors that are sensitive, selective, have long-term stability, and are cost effective O In-situ monitoring of the impedance of ceria-zirconia based TWCs to determine their degree of oxygen loading, o In-situ measurement of the impedance of earth-alkaline oxide-based LNT coating materials to detect the status of an LNT with respect to its NOx-loading, its status of regeneration, its degree of sulfurization, and its thermal aging, o Approaches to determine the ammonia loading in Fe-SCR-zeolites with electrical ac measurements. Radio frequency antennas in the form of simple metallic sticks are inserted into the exhaust pipe and the reflection parameters or the transmission parameters are determined. Such a system measures the catalyst properties in a contactless manner indicating directly the catalyst status.
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