Ammonia Control – The Next Frontier in Automotive Emissions Catalysis
Andrew (Bean) Getsoian, Ford Motor Company
Stuart Daw Memorial Lecture | CLEERS Workshop 2020
Ammonia Control – The Next Frontier in Automotive Emissions Catalysis
Andrew “Bean” Getsoian, Jason Wu, Rachel Snow, Justin Ura, Giovanni Cavataio
Research & Advanced Engineering
Ford Motor Company
Control of NOx emissions from internal combustion engines is a central focus of automotive catalysis. On gasoline powertrains, three way catalysts convert NOx effectively when operated under stoichoimetric or rich (excess reductant) conditions. However, the kinetically most favorable mechanisms for NOx reduction on TWCs generate ammonia, rather than the desired nitrogen gas. On Diesel powertrains, ammonia is purposefully added to the exhaust by decomposition of urea in order to catalyze selective reduction of NOx by ammonia in the SCR catalyst. The latter reactions become more efficient when an excess of ammonia is used. For both engine families, normal driving can readily yield conditions that favor significant tailpipe ammonia emissions. Atmospheric ammonia has been implicated in soot particle formation; and when absorbed into groundwater, ammonia can disrupt ecosystem nitrogen balance to deleterious effect. For these reasons, CARB already issues guidance on ammonia emissions, and regulations on ammonia are under consideration for Euro 7 standards. Gaining greater control over ammonia emissions without compromising control over NOx represents an emerging challenge in automotive catalysis.
This talk will discuss steady state mechanisms for ammonia formation over three way catalysts, the impacts of air-fuel modulation and other transient events on ammonia chemistry, prospects for ammonia decomposition on gasoline and Diesel slip catalysts, and highlights areas where more fundamental research will be needed to enable the next generation of NOx control technologies.
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