The Catalyst Review May 2020 - 18

MOVERS & SHAKERS
Timothy V. Johnson, ScD

Executive Consultant, Corning, Inc
Timothy Johnson received his BS and MS Engineering Degrees from the University of Minnesota and his Doctor of
Science from MIT. Before assuming his current role, he served as Director - Emerging Regulations and Technologies
for Corning Environmental Technologies, where he was responsible for tracking emerging mobile emissions
regulations and technologies and helping to develop strategic positioning via new products. Over the past 23 years,
Tim has become an acknowledged expert and frequent speaker on vehicle emission control technology and trends,
giving nearly a dozen plenary keynote presentations at international conferences. Author of 30 peer-reviewed
publications, he also edited the book, Diesel Filter Technology, published by the Society of Automotive Engineers
(SAE). He has twice testified as an expert witness for the US Senate Environment and Public Works Committee and served on the
editorial board of three leading engine journals. He can be reached at JohnsonT2@Corning.com.

The Catalyst Review asked Dr. Johnson to provide an overview of current and future developments in
the field of automotive catalysis.
This year, the Clean Air Act of 1970 is celebrating its 50th anniversary. Back then, the oxidation catalysts removed about 80%
of the CO and hydrocarbons (HCs) from the exhaust. Although this was a significant improvement, today's modern three-way
catalysts (TWC) for CO, HC, NOx removes 99.5% or more of the 300 ppm of HC+NOx emissions from a modern car engine
with a catalyst residence time of 30 ms. The TWC has often been referred to as the most significant environmental invention
ever. Close behind are the diesel particulate filter (DPF), which cuts diesel tailpipe particulate emissions to concentrations
lower than in urban ambient air, and the selective catalytic reduction (SCR) catalyst, which uses ammonia (from urea) as a
reductant to remove greater than 99% of engine-out NOx from diesel engines once it is warmed up. In China and Europe, it's
the gasoline particulate filter (GPF) that brings the gasoline particulate numbers down to modern diesel levels.
It is now possible to classify prototype urban cars as "negative emissions vehicles," wherein their exhaust has fewer
pollutants than the ambient air although to achieve this level, several advances in emission control will be needed. Cold
start emissions have been the main emissions challenge for more than 25 years. Typically, a TWC is not operative for
15-30 seconds until >250°C is achieved after a cold start, during which time 80+% of the emissions are emitted during a
certification test. Electrically heated catalysts (EHC) could use "brute-force" to quickly light-off the catalyst, and these are
becoming more feasible for HEVs. New low-mass catalyst substrates help accomplish this with or without an EHC. Another
approach involves the use of HC and/or NOx adsorbers that will capture emissions during the cold phase, but release the
collected pollutants after the TWC becomes operative when it reaches 250-300⁰C. A third approach is to drop the catalyst
light-off temperature, and some recent progress dropped the light-off temperature to 210⁰C. However, this is far short of the
industry goal of 150⁰C.
Remediation at cooler exhaust temperatures is also needed as engines become more efficient. Diesel exhaust and leanburn gasoline exhaust can run <200⁰C in city conditions. A TWC will not reduce NOx in an oxygen-rich exhaust, so lean-NOx
catalysts, like SCR, are needed. Ammonia delivery at these temperatures is problematic, so a urea-decomposition catalyst
that makes ammonia at 150⁰C would be useful. Also, zeolite-based SCR catalysts today might convert 50-70% of NOx at
these temperatures, but improvement would be welcome.
Although the above discussion concerns toxic criteria pollutants, the biggest emissions challenge facing the internal
combustion engine (ICE) industry is greenhouse gases (GHGs). On the cutting edge, better CO2 adsorbers are needed to
enable more efficient onboard capture of CO2. Also needed are better "e-fuel" catalysts that will allow for more-efficient
water hydrolysis and subsequent conversion of CO2 with the hydrogen to form liquid fuels. Both approaches can drop
transportation GHGs by the 90% required by 2050 without the vast infrastructure costs of fleet electrification.

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The Catalyst Review

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The Catalyst Review May 2020

Table of Contents for the Digital Edition of The Catalyst Review May 2020