Structural changes in mordenite during its dealuminization

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  1. 1.

    Treatment with acids leads to the dealuminization of mordenite, condensation of pairs of hydroxyl groups in alternate hydroxyl clusters carrying five-membered rings over to four-membered rings. Dehydroxylation proceeds in such way that two OH groups are first eliminated from each of the hydroxyl clusters, without any loss of crystallinity. Loss of crystallinity is observed only on eliminating the second pair of OH groups from the cluster.

  2. 2.

    Hydrothermal treatment of the acid-dealuminized mordenite gives a product with enhanced structural stability. This effect results from the healing of vacancies induced by dealuminization, and from an increase in anion skeleton Si/Al ratio arising from Si and O atom migration, the situation here being similar to that met in the hydrothermal stabilization of H-zeolite.

  3. 3.

    The data suggest that the aluminum atoms which leave the H-mordenite lattice during dehydroxylation do not pass over into the cation state.