UV-visible spectroscopy on Cu-Zeolites, an industrially used catalyst for NOx selective catalytic reduction, result in complex many feature spectra, not easily assigned to specific molecular Cu species. Furthermore, these spectra are highly sensitive to the contacting gaseous environment and temperature of exposure due to exchanged Cu ion mobility within the zeolite[2,3]. Here, we present a precisely coordinated study where Cu-SSZ-13 samples are synthesized and characterized through titrimetric and spectroscopic methods to contain only certain classes of Cu sites, and then assign these Cu species to specific configurations at the molecular level through a novel multi-step computational approach. The computational procedure employed here combines ab initio molecular dynamics, to estimate the macroscopic ensemble of Cu configurations, and time-dependent density functional theory, to compute quantitatively accurate UV-visible spectra, for these species. We show this methodology converges on spectra consistent with those observed experimentally and provides definitive molecular assignments for Cu exchanged cations in real synthesized catalysts. These calculations also provide evidence for what the dominant and minority Cu species are on other zeolite topologies, including MFI, BEA and MOR.
(1) Giordanino, F.; Vennestrøm, P. N. R.; Lundegaard, L. F., Stappen, F. N.; Mossin, S.; Beato, P.; Bordiga, S.; Lamberti, C. Dalton Transactions 2013, 42, 12741−61.
(2) Göltl, F.; Sautet, P.; Hermans, I. Catal. Today 2015, 267, 41−46.
(3) C. Paolucci, A. A. Parekh, I. Khurana, J. R. Di Iorio, H. Li, J. D. Albarracin Caballero, A. Shih, T. Anggara, W. N. Delgass, J. T. Miller, F. H. Ribeiro, R. Gounder and W. F. Schneider
Journal of the American Chemical Society, (2016) DOI: 10.1021/jacs.6b02651
(4) Di Iorio, J. R.; Gounder, R. Chem. Mater. 2016, 28, 2236−2247.