Powder Neutron Diffraction and 29Si MAS NMR Studies of Siliceous Zeolite-Y

Powder neutron diffraction results are presented for two forms of zeolite Y: a sample of Na-Y with a Si/Al ratio of 2.61 (Fd3m, a = 24.703(1) Å) and a sample of siliceous-Y (Fd3m, a = 24.2576(3) Å) which was prepared from dealuminated Y by washing with water and acid followed by subsequent heat treatment. Both zeolites are highly crystalline and show no other crystalline impurities. The structural effects that are caused by the removal of sodium ions and framework aluminium are clearly indicated by changes in the T-O bond distances and temperature factors and related changes in the O-T-O and T-O-T angles. We examine the influence of hydration on the ²⁹Si spectrum of the purely siliceous material and describe our attempts to determine the location of adsorbed benzene in this material.