Cu-exchanged SSZ-13 materials have recently been commercialized as selective catalytic reduction (SCR) catalysts for diesel engine exhaust aftertreatment [1]. Active centers in Cu/SSZ-13 SCR catalysts have been identified as isolated Cu2+ and [CuII(OH)]+ ions. A redox reaction mechanism has also been established, where Cu-ions cycle between CuI and CuII oxidation states during SCR reaction. While the mechanism for the reduction half-cycle (CuII → CuI) is now reasonably well understood [2], only very recently have important elements of the oxidation half-cycle (CuI → CuII) been proposed based on detailed reaction kinetics of low-temperature standard NH3-SCR, spectroscopic studies, and DFT calculations [3]. In particular, kinetic studies suggested that the low-temperature oxidation half-cycle occurs with the participation of two isolated CuI ions, via formation of a transient [CuI(NH3)2]+-O2-[CuI(NH3)2]+ intermediate. Significantly, zeolite structure (topology) plays a central role in enabling this catalytic chemistry. The feasibility of this reaction mechanism was confirmed from DFT calculations, and the simulated energy barriers and rate constants are consistent with experimental findings. Furthermore, this newly proposed low-temperature standard SCR mechanism provides full consistency with detailed low-temperature SCR kinetics. [1] (a) I. Nova and E. Tronconi, Editors, Urea-SCR Technology for deNOx After Treatment of Diesel Exhausts, Springer-Verlag, New York, 2014; (b) A.M. Beale, F. Gao, I. Lezcano-Gonzalez, C.H.F. Peden and J. Szanyi, Chem. Soc. Reviews 44 (2015) 7341-7405. [2] C. Paolucci, A.A. Parekh, I. Khurana, J.R. Di Iorio, H. Li, J.D. Albarracin Caballero, A.J. Shih, T. Anggara, W.N. Delgass, J.T. Miller, F.H. Ribeiro, R. Gounder and W.F. Schneider, J. Am. Chem. Soc. 138 (2016) 6028-6048. [3] (a) F. Gao, D. Mei, Y. Wang, J. Szanyi and C.H.F. Peden, J. Am. Chem. Soc. 139 (2017) 4935-4942; (b) C. Paolucci, I. Khurana, S. Li, A.J. Shih, H. Li, J.R. Di Iorio, J.D. Albarracin-Caballero, A. Yezerets, J.T. Miller, W.N. Delgass, F.H. Ribeiro, W.F. Schneider and R. Gounder, Science 357 (2017) 898-903.

Cu/SSZ-13 catalysts for the selective catalytic reduction of NOx: Unusual features of the complex redox reaction mechanism

255th National Meeting (2018)

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