Zeolite-Encapsulated Copper(II) Amino Acid Complexes: Synthesis, Spectroscopy, and Catalysis

The spectroscopic properties and catalytic behavior of Cu(AA)n m+ complexes (AA ) amino acid (glycine, lysine, histidine, alanine, serine, proline, tyrosine, phenylalanine, glutamine, glutamic acid, cysteine, tryptophan, leucine, and arginine)) in faujasite-type zeolites have been investigated. Successful immobilization was achieved by a simple cation exchange procedure with aqueous solutions of preformed Cu(AA)n m+ complexes. The best ion exchange results were obtained with lysine, arginine, proline (at pH ) 10), and histidine (at pH = 7.3) as ligands and with a AA:Cu 2+ ratio of 5. The internal surface and pore volume are drastically reduced by the uptake of the Cu(AA)n m+ complexes, and no precipitation of Cu(AA)n m+ crystals was observed by scanning electron microscopy. Both observations suggest the location of the complexes in the supercages of the faujasite-type zeolites. The composition of the first coordination sphere around Cu 2+ can be designed from NNNN to NOOO by varying the type of amino acid. A free coordination site is available for catalysis, and the oxidation of alcohols, alkanes, and alkenes with peroxides was observed at low temperatures

Spectroscopy and coordination chemistry of cobalt in molecular sieves

The catalytic potential of Co-containing molecular sieves has simulated zeolite scientists to study the spectroscopyand siting of Co^2+ ions. In this review, a critical overview is given of the spectroscopic tools used: (1) to decide about the cation sites of Co^2+ and their occupancy; (2) to determine the spectroscopic signatures of framework and extra-framework cobalt; (3) to determine the amount of Co incorporated into the framework of molecular sieves; and (4) to discuss local distortions of framework cobalt

Spectroscopy and coordination chemistry of cobalt in molecular sieves

The catalytic potential of Co-containing molecular sieves has simulated zeolite scientists to study the spectroscopyand siting of Co^2+ ions. In this review, a critical overview is given of the spectroscopic tools used: (1) to decide about the cation sites of Co^2+ and their occupancy; (2) to determine the spectroscopic signatures of framework and extra-framework cobalt; (3) to determine the amount of Co incorporated into the framework of molecular sieves; and (4) to discuss local distortions of framework cobalt

Diffuse reflectance spectroscopy of dehydrated cobalt exchanged Faujasite-type Zeolites : a new method for Co2+-siting

The diffuse reflectance spectra of cobalt in X- and Y-type zeolites with varying Co2+ contents have been investigated after dehydration at 400 and 500 degrees C. A novel method for the determination and characterization of Co sites in dehydrated zeolites is developed. The spectra were resolved with a decomposition program in five or six Gaussian bands in the visible region (12 500-22 500 cm(-1)) and three Gaussian bands and two Lorentz bands in the near infrared region (4000-10 000 cm(-1)). Interactive self-modeling analysis showed the presence of three independent Co species, called pure components. In the visible region component A appeared at 20 000-17 800 cm(-1), component B appeared in the 18 800-15 300 cm(-1) region with three band maxima, and component C appeared with main purity at 13 700-14 900 cm(-1). In the near infrared region component B appeared as a triplet in the 4600-7000 cm(-1) region together with two components of framework hydroxyls at 4500 and 7600 cm(-1). With the: aid of additional experiments on dehydrated lanthanum-, cesium-, and ammonium-exchanged Co zeolites, the three cobalt-related components (A, B, and C) were assigned as follows: A, (pseudo)octahedral cobalt in the hexagonal prisms (I); B, (pseudo)tetrahedral cobalt at I' (II',II); and C, trigonally coordinated cobalt at the same sites. These findings are discussed in relation with XRD results of Co siting

Clay intercalated copper(II) amino acid complexes : synthesis, spectroscopy and catalysis

Complexes of Cu(lysine)(2)(2+) and Cu(histidine)(2)(2+) have been intercalated between the layers of saponite clays by a simple cation exchange procedure from aqueous solutions of preformed Cu(amino acid)(2)-complexes. Successful immobilization was obtained with an amino acid:Cu2+ ratio of 5, and a pH of 10 and 7.3 for lysine and histidine, respectively. The synthesized materials were investigated as powders and as thin films by electron spin resonance (ESR), diffuse reflectance spectroscopy (DRS) and X-ray diffraction (XRD). The light blue clays are characterized by an axially symmetric ESR spectrum with A(parallel to) = 192 G, g(parallel to) = 2.23 and g(perpendicular to) = 2.07, and a d-d absorption band around 600 nm, due to the intercalated planar Cu2+-complexes. Ammonia interacts reversibly with these intercalated complexes, suggesting the presence of a free coordination site. The novel synthesized materials are active in various oxidation reactions with t-butyl hydroperoxide as oxidant

Diffuse Reflectance Spectroscopy of Supported Chromium Oxide Catalysts: A Self-Modeling Mixture Analysis

Diffuse reflectance spectra of hydrated, calcined, and reduced chromia/silica-alumina (Cr/SiO2 ¢ Al2O3) catalysts with different SiO2 contents have been investigated by using an interactive selfmodeling mixture analysis. Four pure components are revealed in the spectra of Cr-catalysts before and after calcination: these are component A with three characteristic bands at 225, 325, and 495 nm, component B with three bands at 220, 275, and 400 nm, component C absorbing at 565 nm, and component D which absorbs in the region 205–270–350 nm. Components A and B are due to chromate and dichromate, respectively and their relative ratio increases with decreasing SiO2-content of the support. Component C is assigned to pseudo-octahedral Cr3C and is especially present on SiO2 after calcination, while component D is a background due to the support. After CO-reduction three (E, F, and G) and four (E, F, G, and H) pure components were extracted from the spectra of Cr/Al2O3 and Cr/SiO2, respectively. Components E and G have absorptions around 225, 355, and 475 nm and are due to Cr6C. They decrease with increasing reduction temperature. Component F absorbs at 635 nm on Al2O3 and at 855 nm on SiO2. These bands are assigned to pseudo-octahedral Cr3C and Cr2C, respectively. Pure component H, only present on Cr/SiO2, absorbs at 305 and 540 nm and is possibly due to traces of Cr3C. All these findings are discussed in relation with previous results obtained by spectral deconvolution

Chemometric analysis of diffuse reflectance spectra of Co2+-exchanged zeolites: spectroscopic fingerprinting of coordination environments

A new method for spectroscopic fingerprinting of the coordination environments of Co2+ in zeolites is proposed and discussed. The method is based on the application of different chemometric techniques (curve fitting, Principal Component Analysis (PCA) and SIMPLe-to-use Interactive Self-Modeling Analysis (SIMPLISMA)) on a series of diffuse reflectance (DR) spectra of Co2+-exchanged zeolites dehydrated at 400º and 500°C. Two Co2+ species were determined for CoA and assigned to trigonal and pseudo-tetrahedral coordination of Co2+ at the hexagonal windows of six oxygens. Three components were determined for CoX and COY two of them are similar to those of zeolite A; the third one is ascribed to pseudooctahedral Co2+ in the hexagonal prisms