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. Partridge^b, 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 Laboratory^b

Keywords: Diesel emission control, kinetic model, selective catalytic reduction of NOx, Ammonia SCR, DeNO_x

Abstract

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 Cu^I concentration at steady state. The RHC was found to be second order in oxidized Cu (Cu^II) and first order in NH₃ coverage and NO. The oxidation half cycle (OHC) was observed to be first order in reduced Cu (Cu^I), 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.