KATHERINE 31.WANGAND JACKH.LUNSFORD
1512
An Electron Paramagnetic Resonance Study of Y -Type Zeolites.
I. 0,- on Alkaline Earth Zeolites by Katherine M. Wang and Jack H. Lunsford Department of Chemistry, Texas A&M University, C O ~ ~ Station, E Q E Texas YY843
(Received August 20,1969)
Interactions between the adsorbed 02- species and alkaline earth Y-type zeolites have been studied by means of epr spectroscopy. The adsorbed 02- was formed by uv or y irradiation of the zeolites in oxygen. The results show that there are three or more different adsorption sites on each of the cationic zeolites. The spectra have been placed into three groups according to their g values and response to the two types of irradiation. Within each group there does not appear to be any significant trend in the energy splitting, A, of the 2 p ~ , *levels of the 02- ion as one goes up the series from BaY to MgY. The CaY zeolite was also studied after extensive y irradiation of the sample under vacuum. Three paramagnetic centers were also formed under these conditions; two were identified as V-type centers and the other as an F-type center.
Introduction Pickert, et ul.,l calculated the electrostatic field for a number of points in purely ionic models of CaX and CaY zeolites. I n these models, several restrictions were made. The net negative charge associated with each A104 tetrahedron was assumed to reside on the AI ion; each 6-ring contained exactly two aluminums, and these two aluminums must be apart as far as possible; a “double basket” unit of structure was formed by the pairs of adjacent sodalite units with‘ their associated calcium ions of sites I and 11, and this “double-basket” unit has zero net electric charge and zero dipole moment. According to their results the electrostatic field is much stronger for an occupied site than it is near an unoccupied site. The effective field for polarization is stronger at a shorter distance of approach; therefore, a stronger field should be expected for a smaller cation. Also, they proposed that the electrostatic field was responsible for the catalytic activity of the zeolites. A number of attempts have been made to verify experimentally the presence of these unusually large fields and to show that they varied in a systematic manner as predicted. One of the most convincing pieces of evidence is from the work of I
