Kinetic modeling of NO selective reduction with C3H6 over Cu-SSZ13 monolithic catalyst

Abstract

• Kinetic model for lean NO reduction with C 3 H 6 on Cu/CHA monolith is developed. • Model includes the key intermediates detected by DRIFTS. • Model predicts steady state C 3 H 6 and NO conversions vs. temperature quantitatively. • Model predicts transient behavior for C 3 H 6 + O 2 and C 3 H 6 + NO + O 2 reaction systems. • Model provides useful insights into non-ammonia pathways for lean NO x reduction. A mechanistic-based kinetic model is developed for selective catalytic reduction of NO with C 3 H 6 on Cu chabazite (Cu-SSZ13) monolithic catalyst based on bench scale flow reactor studies and in-situ DRIFTS measurements. The SCR mechanism involves reaction between oxygenates (partially oxidized hydrocarbon species) and NO to form isocyanates species ( NCO), detected by DRIFTS, which are further reduced to N 2 . We have shown in an earlier study that reaction intermediates, most likely surface isocyanates, poison the active sites on the catalytic surface resulting in the inhibition of other reactions (Raj et al., 2013 [7]). The kinetic model was developed in steps, starting with steady-state CO oxidation, followed by C 3 H 6 oxidation, and then the C 3 H 6 + NO + O 2 reaction system. This approach ensured consistency in the parameter estimation and resulted in a more robust model. The models for CO + O 2 , C 3 H 6 + O 2 and C 3 H 6 + NO + O 2 were also validated using a new set of steady state experiments. The monolith model predicts the observed negative order with respect to C 3 H 6 and positive order with respect to O 2 for the C 3 H 6 oxidation reaction. For the C 3 H 6 + NO + O 2 reaction system, the predicted NO and C 3 H 6 conversions agree well with both steady state and transient experimental data. The model captures the significant shift of C 3 H 6 light-off to higher temperature in the presence of NO due to formation of the inhibiting NCO surface species as well as slow transients associated with surface intermediates and their effect on the extent of reactions.