CLEERS SCR Focus Technical Priorities
The scope of work for the CLEERS Selective Catalytic Reduction (SCR) focus area is to develop
sub-models (maps) that describe the details of catalyst performance relative to primary and
competing reactions for inclusion in device-scale models. A key function of the SCR Focus
Group is to also promote and identify research activities important to improving the simulation
of SCR processes and catalyst materials. The primary SCR technology focus is currently on nonVanadia based urea-SCR systems, with a secondary focus on hydrocarbon (HC) SCR processes
(lean-NOx).
The development of advanced modeling capabilities and analytical tools to interigate and
simulate the operation and performance of urea- and HC-SCR systems are very much needed.
These new tools will provide researchers and engineers with the tools to enhance and extend the
design, durability and operational boundaries of SCR ssytems. The technical topical areas of
interest and needs for research related to SCR processes and associated catalyst materials are:
1. Global reaction rate equations
 Define types of global rate equations
 Development of competing/complementary sub-models that describe the details of
different aspects of the SCR process
a. Urea decomposition on surface
b. HNCO decomposition on surface
c. Urea reaction with NO &NO2
d. Urea & HNCO surface oxidation rates
 Mechanistic studies of effective hydrocarbons and intermediate species for lean-NOx
reductants.
2. Dosing system
 Spatial and temporal distribution of urea/NH3 or HCs in exhaust system
 Thermolysis/hydrolysis process
 Aerosol quality
 Atomizer placement variable
 Exhaust gas temperature effects
3. Deactivation mechanisms
 Thermal degradation due to cycling
 Catalyst poisoning
 Soot, ash, coking
 Other by-product contamination
 Other aging phenomenon
4. Characterization/definition of storage and release mechanisms
 Adsorption/desorption mechanisms for ammonia and hydrocarbons
 Decomposition of urea and/or isocyanate on catalyst surface
5. Species transport effects
 Mobility of catalyst particles within the support
 Pore/washcoat diffusion effects
 Adsorption isotherms
6. Contaminants/by-products of NOx and reductant decomposition
DRHerling 07MAR05