Cu-CHA deNOx catalyst: structure-performance relationship elucidated by X-ray absorption and emission spectroscopy

Cu-CHA is an outperforming catalyst for the NH₃-assisted selective catalytic reduction (SCR) of the harmful nitrogen oxides (NO_x, x=1, 2). However, a comprehensive picture of the relationship between performance of this promising zeolite and structure of its active sites is only beginning to emerge. It has been shown that the catalytically active centers for SCR reaction may be represented by isolated Cu ions hosted in the cavities of zeolitic framework, so the element-selective studies of Cu local environment are crucial for understanding of the enhanced catalytic properties of this material [1]. Therefore, we employed synchrotron-based XAS and XES spectroscopies complemented by DFT calculations and laboratory techniques to elucidate the nature and location of the most abundant Cu-sites in a highly active Cu-CHA catalyst (Si/Al and Cu/Al ratios of 13.1 and 0.44 respectively) in activated state [2,3], in different reaction-relevant conditions [4,5] and in operando regime during the reaction with the SCR mixture [6]. The seminar will be focused on the results of these studies, which allowed us to suggest a consistent mechanism for NH₃-SCR reaction, prove its key steps characterizing the intermediate species and describe the Cu speciation under SCR conditions at different temperatures.

[1]        K.A. Lomachenko, E. Borfecchia, S. Bordiga, A.V. Soldatov, P. Beato, and C. Lamberti, J. Phys.: Conf. Ser., 712, 012041 (2016).

[2]        F. Giordanino, E. Borfecchia, K.A. Lomachenko, A. Lazzarini, G. Agostini, E. Gallo, A.V. Soldatov, P. Beato, S. Bordiga, and C. Lamberti, J. Phys. Chem. Lett., 5, 1552-1559 (2014).

[3]        E. Borfecchia, K.A. Lomachenko, F. Giordanino, H. Falsig, P. Beato, A.V. Soldatov, S. Bordiga, and C. Lamberti, Chem. Sci., 6, 548-563 (2015).

[4]        C. Tyrsted, E. Borfecchia, G. Berlier, K.A. Lomachenko, C. Lamberti, S. Bordiga, P.N.R. Vennestrom, T.V.W. Janssens, H. Falsig, P. Beato, and A. Puig-Molina, Catal. Sci. Technol., Accepted, DOI: 10.1039/C1036CY01820C (2016).

[5]        T.V.W. Janssens, H. Falsig, L.F. Lundegaard, P.N.R. Vennestrøm, S.B. Rasmussen, P.G. Moses, F. Giordanino, E. Borfecchia, K.A. Lomachenko, C. Lamberti, S. Bordiga, A. Godiksen, S. Mossin, and P. Beato, ACS Catal., 5, 2832-2845 (2015).

[6]        K.A. Lomachenko, E. Borfecchia, C. Negri, G. Berlier, C. Lamberti, P. Beato, H. Falsig, and S. Bordiga, J. Am. Chem. Soc., 138, 12025−12028 (2016).