Szilard-Chalmers and X-ray Absorption Spectroscopy to Locate Copper Cations in Synthetic Faujasite, Zeolite X
- PDF / 419,367 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 91 Downloads / 175 Views
Szilard-Chalmers and X-ray Absorption Spectroscopy to Locate Copper Cations in Synthetic Faujasite, Zeolite X Syed M. Khalid Photon Science Division, National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY 11973, U.S.A. ABSTRACT The sodium in synthetic faujasite, commercial zeolite-X, was exchanged with copper cations at room temperature. A maximum number of 70 out of 86 Na cations were replaced with 35 copper cations ( 1 ). The copper exchanged zeolite was divided in six equal parts. Five of them were calcined at 43, 73, 112, 150 and 195 deg C. After calcination the samples were eluted with saturated solution of ammonium chloride to remove copper cations from open sites (super-cages) of the zeolite ( Fig 1 ). The remaining copper cations were in locked sites (sodalite-cages or hexagonal-prisms). Using XAS edge-jump as a measure of quantitative analysis, we found that 9.0, 11.5, 12.7, 13.3 and 20.0 copper cations were locked at calcination temperatures of 43, 73, 112, 150 and 195 deg C respectively. The analysis of the first shell Fourier Transformed radial distribution shows that cations at site I in the hexagonal-prism and site I ‘ and II ‘ in the sodalitecages, adjacent to site I, are distributed at equal proportion, independent of temperature. . INTRODUCTION The knowledge of distribution of cations in zeolites is essential for selecting a zeolite for its catalytic and molecular sieve properties. Szilard and Chalmers first observed that when ethyl iodide was exposed to thermal neutrons, the iodine atoms recoiled after capturing a neutron, resulting in breaking the iodine bond from ethylene. Szilard-Chalmers recoil effect as Neutron Activation Analysis (NAA) was used in the past (1) to find the percentage of cations remained in the locked sites of zeolites after calcination (Fig 1). Szilard-Chalmers recoil percentage from the open sites (super-cages) to the locked sites (about 90%) and from the hexagonal prism sites to the open sites (about 50%) was used to find the distribution of these cations at site I in the hexagonal prisms and site I ‘ and II ‘ in the sodalite cages, adjacent to the shared and unshared six ring respectively. NAA technique involves the radiation emission of the nuclei after being irradiated with high dose of thermal neutrons. After the neutron capture the combined mass of nucleus is less than the sum of the separate masses of neutron and the nucleus. The excess mass is released in the form of gamma rays as spontaneous large energy of about 8 MeV per nucleon binding energy according to Einstein’s mass-energy relation. In the process of this spontaneous emission the cations recoil to different positions within the framework of the zeolite. The elution percentage of the radioactive cations was an indirect measure of the location of those cations at different sites (2). In NAA we deal with the production and handling of radioactive samples, as a result of that, radioactive waste was generated with some of the isotopes having very long half-life. The
disposal of this waste i
Data Loading...
