Global kinetic models for reduction and oxidation half-cycles of the NH3-SCR redox cycle: application for quantifying active Cu sites and aging of Cu-zeolite catalyst
Saurabh Joshi, Cummins Inc.
Global kinetic models for reduction and oxidation half-cycles of the NH3-SCR redox cycle: application for quantifying active Cu sites and aging of Cu- zeolite catalyst
Saurabh Y. Joshi, Rohil Daya, Rama Krishna Dadi, , W.P. Partridgeb, Ashok Kumar, Yadan Tang, Dylan Trandal, Krishna Kamasamudram, Michael Cunningham, Aleksey Yezerets
Corporate Research and Technology, Cummins Inc., 1900 McKinley Avenue, Columbus, IN 47201, U.S.A.
Oak Ridge National Laboratoryb
Keywords: Diesel emission control, kinetic model, selective catalytic reduction of NOx, Ammonia SCR, DeNOx
We developed global kinetic models for the reduction and oxidation half-cycles of the NH3-SCR redox cycle over a state-of-the-art Cu-SSZ-13 catalyst. Experiments were performed to determine the kinetic parameters of each individual half cycle. The reduction half cycle (RHC) experiment involved switching NH3 to a feed consisting of NO, 7% H2O, 8% CO2 and N2. The lack of O2 in the feed prevented Cu reoxidation, resulting in maximum CuI concentration at steady state. The RHC was found to be second order in oxidized Cu (CuII) and first order in NH3 coverage and NO. The oxidation half cycle (OHC) was observed to be first order in reduced Cu (CuI), NO and NH3 coverage. The global SCR redox model could predict previously reported SCR onset conversion inflections (CI), characterized by fast conversion growth to an intermediate value greater than steady state conversion. CI occur because the rate of RHC gets significantly accelerated compared to OHC at higher temperature due to higher apparent activation energy. Further it was shown that the CI was found to be more distinct at higher temperatures and towards the catalyst front. The redox model was utilized to study the impact of aging on the kinetic parameters and number of active Cu sites in a state-of-the-art Cu-SSZ-13 catalyst.