THE STATUS OF CHROMIUM IN ALUMINUM-FREE CHROMOSILICATE WITH THE ZSM-5STRUCTURE

It is shown that the hydrothermal synthesis of aluminum-free chromosil icate results in the formation of crystalline zeolite with the ZSM-5 s tructure and some Cr3+ ions substitutes isomorphically for Si4+ ions i n the lattice of as-made samples. After oxidative calcination most chr omium ions aggregate in alpha-Cr2O3 microcrystals on the outer surface of the zeolite. However, some chromium remains stabilized strongly in the zeolitic structure as isolated low coordinated Cr(V) ions in two discrete coordinative states. It may be supposed that Cr(V) ions chemi cally bonded with zeolite lattice also have out of lattice ligands and are capable of interacting specifically with different molecules.