Conduction and relaxation of cations in dehydrated partially copper(II)-exchanged synthetic faujasites

Abstract

The electrical conductivity and dielectric relaxation of dehydrated synthetic faujasites X and Y with various Cu2+-contents are measured at temperatures between ambient and 750 K and in the frequency range x lo6 Hz.The supercage cations are responsible for the conduction process. At exchange levels below 11-14 Cu2+ ions per unit cell these are Na+ ions. At higher exchange levels a low temperature and a high temperature conduction process are evident, due to Na+ and Cu2+ ions, respectively, in the supercages. The activation energies and entropies for Na+ conduction decrease with increasing Cu2+ in the small cages : 74-32 kJ rnol-' and -20 to -150 J mol-I K-l, respectively. The activation energy and entropy for Cu2+ conduction are 120+ 10 kJ mol-l and -9+ 13 J mol-' K-', respectively. They both decrease significantly in the presence of protons.In the experimental temperature and frequency ranges 3 relaxations were observed. In order of decreasing critical frequency at a given temperature they were assigned to (i) local migration of site 111' cations between two occupied sites 11, (ii) cationic jumps confined to the sodalite cages and (iii) electrode polarizations. A model explaining the variation of the intensities of relaxation (i) and(ii) with degree of Cu2+-exchange and with the temperature is proposed.Excess Cu is present in an unidentified hydroxylated form and does not intervene in the ionic processes studied.The replacement of Na+ by Ca2+ in the hexagonal prisms and sodalite cages of synthetic faujasites resulted in a significant decrease of the activation energy for migration of the supercage Na+ ions.'-Furthermore a cationic relaxation due to these Ca2+ ions in the small cavities was observed. These measurements allowed a distinction to be made between exchangeable cations in the supercages and in the dense cages. For the latter no discrimination between exchangeable cations in the hexagonal prisms and in the cubo-octahedra was possible.The distribution of Cu2+ ions in dehydrated synthetic zeolites, types X and Y , is unusual as compared with other divalent cations, in that Cu2+ strongly prefers the sites I' in the sodalite ~avities.~'lO The question arises as to how far these differences of partition of Ca2+ and Cu2+ among sites I and I' are reflected in ionic conduction due to supercage cations. Moreover, if the differences in distribution of Ca2+ and Cu2+ among sites I and I' are reflected in the ionic relaxation, a combination of electric conduction and dielectric relaxation measurements may be used to investigate quantitatively the distribution of exchangeable cations among different sites. Such measurements, when performed over an extended temperature range, will enable the investigator to gain insight into the relative potential energies of exchangeable cations on their sites. EXPERIMENTALSamples were prepared in different ways and their cation contents axe given in table 1 together with the symbols defining them used throughout the text. The number after the symbols is the Cu-content in percent of...

Spectroscopic characterization and thermal stability of copper(II) ethylenediamine complexes on solid surfaces. 1. Synthetic faujasites types X and Y

“…At low exchange levels all the Cu2+ ions are located in the small cavities of the dehydrated structure (hexagonal prisms and cubooctahedra). 34 The reflectance spectrum observed for CuY-3 indicates a gradual decrease of uncomplexed Cu2+ ion concentration and a gradual increase of a band at 16200 cm"1 with increasing en loadings. Since the latter band remains at the same position even in excess en, and its frequency is close to that of Cu(en)32+,20-22 we believe that the tris complex is formed.…”

EPR and 129Xe NMR Studies of Copper-Exchanged NaY Zeolites

“…Also in high copper content samples, some of Cu2+ are located in supercages as indicated in the conduction measurements. 18 Thus it is plausible the Cu2+ site corresponding to the spectra observed at high temperature for CuNaY-5 in the presence of O2 adsorbate (Figure 1), and spectra 4b,e-h are the same and are most likely located in the sodalite cages or in the peripherals of supercages.…”

Conductivity of Mono- and Divalent Cations in the Microporous Zincosilicate VPI-9

“…Zeolite X and zeolite Y (framework topology FAU) have received considerable attention and exhibit among the best reported ionic conductivities among zeolites and zeolite-like materials. − Numerous research efforts have been devoted to characterizing the ion conducting properties of zeolite X and Y, as well as understanding internal relaxation properties occurring within the α cages of these zeolites. Zeolites X and Y have also been used as standards in characterizing new materials, and data on zeolite X are presented herein alongside the VPI-9 data, and in the Supporting Information in modulus representation.…”