ATOMIC-STRUCTURE OF SELENIUM INSERTED IN ZEOLITES OF THE NA-MORDENITETYPE

The atomic structure of Se incorporated with various amounts in both s mall and large pore zeolites of the Na-mordenite type is investigated by X-ray absorption spectroscopy (XAS). The results of the EXAFS analy sis are compared to those obtained for hexagonal selenium. The distanc es of Se to its first and second Se neighbors are found to be 2.33 and 3.61 Angstrom, respectively, and attributed to intrachain distances, which are reduced with respect to those of hexagonal selenium. The lac k of the Se-Se distance at 3.44 Angstrom confirms the loss of the firs t interchain bonds present in hexagonal Se and confirms the incorporat ion of single chains of Se in the channels of the mordenite in agreeme nt with previous results given in the literature. Only small differenc es in the selenium environment are observed for the Various contents o f Se in mordenite. The presence of a peak around 4 Angstrom in the Fou rier transforms of the EXAFS data of all the analyzed compounds is att ributed to the partial overlap of the single Se chains present inside the mordenite channels.