Electron Paramagnetic Resonance Study of Chromosilicalite

Abstract

The catalytic importance of chromium has prompted numerous attempts to introduce chromium cations in zeolites. For example, Naccache and Ben Taarit,' Atanasova et aL2 and Pearce et d3 have investigated the Cr species mainly in A, X, and Y zeolites, whereas Hemidy et aL4 and Kucherov and Slinkin' reported results for the Cr-mordenite system. In a recent communication6 we reported the incorporation of Cr3+ in the structural positions of ZSM-5 type zeolites, and recently we have demonstrated the incorporation of oxygen in this zeolite with oxidation of anchored Cr3+ to noninteracting Cr6+ species.' Here an EPR study of crystalline chromosilicalite is presented with the purpose of further characterizing the distributon of each Cr3+ site in the solid. Such characterization is a necessary prelude to establishing the chromosilicalite activity as a catalyst in the production of alkenes. In addition a deconvolution process is described whereby the EPR parameters could be analysed. This method proved to be quite successful, and the results provide evidence that Cr3+ ions are at least in two substitutional-like or highly distorted sites and in another one outside the silicon framework.