H-[CR]ZSM-5 ZEOLITE - FEATURES OF STABILIZATION AND PROPERTIES OF CHROMIUM IONS INTRODUCED DURING THE SYNTHESIS STAGE

It has been shown that in the synthesis of the chromosilicate zeolite H-[Cr]ZSM-5, part of the Cr3+ ions enter isomorphically into the zeolite framework. Calcination of these zeolites in air leads to aggregation of most of the chromium that has been introduced, forming Cr2O3 crystals on the external surface of the zeolite. A small fraction of the chromium ions remains in the zeolite structure, strongly stbilized in the form of isolated, low-coordination Cr(V) ions, of two discrete types. It is believed that these ions remain chemically bonded to the framework but also have extralattice ligands, and that this is responsible for their capability of specific interaction with various molecules.