FINE CONTROL OF THE PORE-OPENING SIZE OF ZEOLITES BY CONTINUOUS-FLOW TYPE CVD METHOD

By using a continuous-flow type CVD (chemical vapor deposition) method, a large amount of zeolite can be modified to finely control the pore-opening size. In this investigation, modification of zeolite A by Si (OCH3)4 is described as an example, and the modified CVD-A zeolite is characterized by N2 adsorption measurement and surface analysis with XPS. When the zeolite is pretreated sufficiently by flowing dry helium at 673K, it is modified uniformly along the bed. This is caused by a low concentration of sorbed water and/or hydroxide. The amount of deposited silica can be controlled by repeating deposition-hydrolysis cycles. The extent of narrowing the pore-opening size is determined only by the deposition amount of silica, which is estimated to be a mono to triple layer. The relationship between the extent of control and the deposition amount of silica is not influenced by deposition conditions. © 1990, The Society of Chemical Engineers, Japan. All rights reserved.