Raman and X-ray absorption study of selenium incorporated into the channels of mordenite: Dependence on the ion exchange and the method of incorporation

Abstract

Influence of ion exchange and method of selenium incorporation into mordenite channels on the structure of incorporated selenium species are studied by Raman and X-ray absorption spectroscopy. It is shown that Se chains prepared by Se vapor adsorption are more regular than Se chains prepared by pressure injection of liquid Se. Concentration ratio between Se chains and Se 6 rings is found to be practically independent of the method of preparation but dependent on the type of cations in mordenite channels. Substitution of Na cations by larger monovalent cations leads to a decrease in Se chains concentration compared to Se 6 rings concentration and to an increase in average SeSe bond length. X-ray absorption spectrum of M-Se for polarization of radiation perpendicular to the channels is shown to be determined mainly by Se6 rings, and that for polarization parallel to the channels is a superposition of the absorption of chains and rings. Selenium incorporated into H-form of mordenite is found to be located not only in the original mordenite channels, but also in meso-channels organized due to partial destruction of the interchannel walls.