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.

Spectroscopy and Redox Chemistry of Copper in Mordenite

“…This Cu 2 + ion type has also been reported to readily reduce by reaction with CO at elevated temperatures. [35] The reduction occurs with the selective disappearance of the EPR signal at 2 g j j = 2.27, along with the d-d transition envelope at 16 750 cm À1 . Therefore both spectroscopic features unambiguously belong to the same mononuclear Cu 2 + species.…”

“…Knowledge of the spectroscopic characteristics led to a refinement of the Cu sites and their coordination characteristics in CuMOR. [35] The identified monomeric Cu 2 + species make up almost 30 % of the total Cu fraction. The dominant Cu species is likely a binuclear copper site, but other autoreducible EPRsilent Cu species cannot be ruled out.…”

“…[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] Location of TMIs in zeolites and their coordination is thus established for many zeolite topologies and zeolite compositions. [1] Often these spectroscopic studies focused on low transition metal contents, [35][36][37][38]51] while the best catalytic results were mainly reported with high Cu 2 + loadings. Despite the complex-ity, we believe that an appropriate combination of spectroscopy, reactivity and theoretical studies will offer unique opportunities to identify novel active sites, also in highly loaded Cuzeolite samples.…”

“…The 6-MRs were geometry optimized with DFT and the spectra were calculated on the optimized structures with CASPT2. The conclusions of those studies were: [35,42,43,62] · Cu 2 + attempts to acquire its maximum coordination number of 4. · In this 4-fold coordination, Cu 2 + preferentially coordinates with O atoms belonging to the Al tetrahedron and as a result, the 6-MR is strongly distorted.…”

Homogenous and Heterogeneous Catalytic Activity of Azo-Linked Schiff Base Complexes of Mn(II), Cu(II) and Co(II)

“…The mixture was then stirred for 24 h. The solid was filtered and washed with de-ionized water and dried at room temperature to give a light blue powder of Cu-NaY [30]. Calcination of the prepared copper(II)-incorporated zeolite was avoided to arrest the migration of copper (II) ions from the vicinity of the super cage [31].…”