THE STATE OF TRANSITION-METALS AND THEIR DISTRIBUTION IN SURFACE-LAYERS OF HIGH-SILICA ZEOLITE CRYSTALS .5. IR-CONTAINING PENTASILS

As shown by the XPS method, the oxidation treatment of Ir/HZSM-5 zeoli tes prepared by impregnation with H2IrCl6 leads to transformation of I r(IV) into Ir(III) and to cation migration inside the zeolite crystals in the course of the reaction in the solid phase. Large Ir(O) particl es are formed at the outer surface after reduction or after low-temper ature calcination followed by reduction. Treatment in hydrogen of the samples precalcined at 673 - 773 K leads to stabilization of highly di spersed iridium in a zeolite structure.