ESR study of CuSSZ13 for removing NOx by NH3

In-Sik  Nam, Pohang University of Science and Technology (POSTECH)

Small-pore zeolite catalyst, particularly CuSSZ13, has been drawing keen interest from auto industry as a highly promising commercial catalyst for the urea/SCR system due to its excellent low-temperature activity and robust hydrothermal stability [1]. Despite extensive efforts in recent years to understand the catalytic characteristics of CuSSZ13 catalyst [2,3], the local environment of Cu2+ ions still remains unclear. In the present study, the hydrothermal stability of a series of CuSSZ13 catalysts containing a wide range of Cu contents and Si/Al ratios has been investigated along with their deactivation mechanism. The decline of the deNOx activity over the CuSSZ13 catalyst by the hydrothermal aging at 850 oC becomes more severe as the Cu content and/or the Si/Al ratio increases. Results of ESR, H2-TPR and DRIFT studies indicate that Cu2+ ion is first coordinated on the D6R up to the saturation of the site, and then the other site in the CHA cage started to be occupied by Cu2+ ion with the increase of the Cu content and Si/Al ratio in the CuSSZ13 [3]. Cu2+ ion in the CHA cage aggregates more readily than that on the D6R due to its less stable nature, leading to the formation of CuOx. The CuOx may grow to destroy the zeolite cage and channel, resulting in the collapse of the SSZ13 structure, which is believed to be the primary cause for the hydrothermal deactivation of the CuSSZ13 catalyst [4].

[1] D.W. Fickel, E. D’Addio, J.A. Lauterbacha, R. F. Lobo, Appl. Catal. B, 102 (2011) 441.
[2] U. Deka, A. Juhin, E.A. Eilertsen, H. Emerich, M.A. Green, S.T. Korhonen, B.M. Weckhuysen, A.M. Beale, J. Phys. Chem. C, 116 (2012) 4809.
[3] J.H. Kwak, H. Zhu, J.H. Lee, C.H.F. Peden, J. Szanyi, Chem. Commun., 48 (2012) 4758.
[4] K.C.C. Kharas, H.J. Kobota, D.J. Liu, Appl. Catal. B, 2 (1993) 225.