EPR STUDY OF THE DISTRIBUTION OF GD3-5 ZEOLITE( AND CU2+ IONS IN HZSM)

The distribution and mutual effect of Gd3+ and Cu2+ ions in HZSM-5 zeo lites depending on the conditions of zeolite thermal treatment and the order of component introduction into the zeolites are studied by X-ba nd EPR. The interacting lanthanide cations are stabilized in the initi al impregnated samples. The calcination of Gd/HZSM-5 in air at 500-900 degrees C is accompanied by the dispergation of a substantial portion of Gd3+ and stabilization of isolated ions in several distinguishable coordinations, The appearance of EPR lines with g = 5.8 and 2.8 point s to partial localization of Gd3+ ions in the zeolite framework as a r esult of isomorphous substitution of Al3+ cations. In addition to the framework ions, small clusters of Gd3+ cations, which are localized in zeolite channels, are also formed in the system. In the calcined samp les, EPR signal of these clusters is not observed because of dipole-di pole broadening. Hydration leads to the decomposition of clusters, and an intense EPR signal with g = 1.98 appears. In contrast to HZSM-5 ze olites, the surface of amorphous aluminocilicate does not stabilize Gd 3+ clusters. The presence of lanthanide ions insignificantly affects t he stabilization of isolated Cu2+ cations in HZSM-5. The distribution of Gd3+ and Cu2+ ions after oxidative calcination of the (Gd + Cu)/HZS M-5 system does not depend on the order in which the components are in troduced. The distribution and properties of copper ions in (Gd + Cu)/ HZSM-5 precalcined at 500-550 degrees C are almost identical to those in Cu/HZSM-5 where copper ions occupy cation positions. However, high- temperature conversions of Cu2+ in (Gd + Cu)/HZSM-5 occur much slower than in Cu/HZSM-5.