EFFECT OF AGING OF HIGHLY SILICEOUS Y-TYPE AND ZSM-5-TYPE ZEOLITES BYIR SPECTROSCOPIC DATA

The changes in the structure of highly siliceous Y- and ZSM-5-type zeo lites during prolonged aging in air have been studied by IR spectrosco py. At relatively low (<20) Si/Al ratios, gradual improvement of the z eolite structure is observed, which is related to ordering of the cati onic and anionic sublattices. As a rule, this is accompanied by symmet rization of the tetrahedral framework units and decrease of the excess ive negative charge of the framework. At higher Si/Al ratios, the zeol ite structure transforms into stable crystalline silica modifications, alpha-cristobalite (in the case of highly siliceous analogs of Y zeol ite) and alpha-quartz (in the case of ZSM-5-type zeolites).