Factors affecting the steam dealumination of zeolite omega

Three samples of zeolite omega with varying residual contents of sodium have been dealuminated by combined steam and acid treatments. The hydrolysis of the AlO bonds is a fast process that occurs mainly during the initial period of heating above 500° under steam. Sodium ions inhibit the reaction. The steamed solids contain mesopores ≅ 100 Å in diameter, but their porosity is not available to sorbents because of the presence of debris in which aluminum is in tetrahedral and octahedral configurations. Acid leaching removes all the nonframework tetrahedral aluminium and part of the octahedral one. This removal permits access to the microporous and mesoporous voids. Increasing the severity of the steam treatment increases the quantity of the disloged material that cannot be removed by the acid, but has little effect on the texture of the final solids. The TEM observations and the volumetric measurements suggest that the mesopores are not directly linked to the surface of the grains and are connected to each other by narrow necks.