The Coordination of CuII in Zeolites − Structure and Spectroscopic Properties

Abstract

Keywords: Zeolites / Copper / Ab initio calculations / Density functional calculations / ESR spectroscopy / UV/Vis spectroscopy / Heterogeneous catalysis Zeolites loaded with transition metal ions are promising heterogeneous catalysts. Knowledge about the location and structure of the metal centers is of paramount importance for the understanding of the catalytic potential of these materials. In this work, the spectroscopic studies of the coordination of Cu II in zeolite A, ZK4, X, Y and mordenite are reviewed. Experimentally, diffuse reflectance spectroscopy [a] teaches general chemistry and computational chemistry. Her main research interest is the application of ab initio methods for the study of spectroscopic and magnetic properties of systems containing transition metals. Marijke H. Groothaert (left center) was born in Neerpelt, Belgium in 1975. In 1998 she received her M. S. degree from the . Since 1998 she is a PhD student at the Center for Surface Chemistry and Catalysis under the supervision of Professor Robert A. Schoonheydt. Her research is concentrated on the coordination of transition metal ions in zeolites and combines spectroscopic techniques with computational methods. Robert A. Schoonheydt (left bottom) received his M. S. degree in 1966 and . Hab. in Leuven, where he teaches quantum chemistry, computational chemistry, and inorganic chemistry. His main research interests are in the application of computational methods in different areas of chemistry.MICROREVIEWS: This feature introduces the readers to the authors' research through a concise overview of the selected topic. Reference to important work from others in the field is included. 515(DRS) and electron spin resonance (ESR) spectroscopy have been applied to study the coordination of Cu II in zeolites. Ab initio calculations on model clusters, representing the Cu II sites in zeolites, are used for the interpretation of the experimental data. The combination of experimental spectroscopic information with theoretical results leads to a new and profound insight into the Cu II −zeolite interaction.

Study of propane oxidation on Cu-zeolite catalysts by in-situ EPR and IR spectroscopies

“…Nevertheless, from comparison of the parameters shown in Table 2 with those reported in the bibliography for other Cu 2+ exchanged zeolites [37], signals A and B can be attributed to Cu 2+ in square pyramidal and square planar configurations, respectively. Figure 2b displays the spectrum recorded after the adsorption 2 molecules of C 3 H 8 per Cu atom on Cu-TNU-9.…”

Transition-Metal Ions in Zeolites: Coordination and Activation of Oxygen

“…In the work of Schoonheydt and co-workers,49-54 a set of Cu-containing zeolites was studied with UV-vis-NIR absorption and EPR spectroscopies. Examples of EPR spectra are shown in Figure 3, and the d-d transitions and EPR parameters of these Cu 2+ sites are summarized in Table 3.…”

“…A ligand field analysis of the d-d transitions of Co 2+ and Cu 2+ in six-ring sites indicated that the TMI are not symmetrically coordinated in the center of the ring, but undergo an off-axial displacement 55-58. Detailed ab initio quantum-chemical analysis revealed that coordination of Cu 2+ or Co 2+ in a specific exchange site leads to a strong site distortion 49, 51-54. First, the TMI try to maximize their coordination number.…”

Observation of Single-Crystal-Type EPR Spectra from Monolayers of Copper-Exchanged Zeolite Na-A Crystals Assembled on Glass Plates

“…24 It is well-known that Cu 2+ has a strong preference for a square planar coordination, and ab initio calculations on a copper complex in the six-ring plane have suggested that Cu 2+ is coordinated to three O(3) and one O(2), forming a distorted square plane. 10,13 Still, as long as Cu 2+ lies in the six-ring plane, the g z direction should be parallel to [111], contrary to our finding that it is tilted only 9°a way from the c axis. A trigonal complex with Cu 2+ displaced from the six-ring plane into the cage is more compatible with our finding.…”

“…[11][12][13] All EPR studies, however, have been carried out with powder samples, and g z directions of the copper species have never been determined experimentally. In ESEEM studies the g z directions of all species were assumed to be parallel to [111] of the cubic unit cell.…”