SYNERGETIC EFFECTS IN THE Y-ZSM-5 ZEOLITE SYSTEM .1. HYDROTHERMAL STABILITY OF HYDROXYL-GROUPS IN THE HY-HZSM-5 SYSTEM

The hydrothermal stability of hydroxyl groups in the HY-HZSM-5 system (stabilized and unstabilized) was investigated. HNaY and HNaZSM-5 zeol ites had greater hydrothermal stability in mixtures than in unmixed fo rms. Mixtures simultaneously stabilized were as good as USY alone; no dehydroxylation was detected during water vapour interaction. NMR MAS measurements indicated the presence of extralattice aluminium phases. The influence of unextracted extralattice aluminium phases during simu ltaneous stabilization or activation by dehydroxylation is possible. A cid Bronsted centre concentrations and specific surface area were meas ured. Zeolite structure was preserved after mixing by milling or water vapour interaction.