Acidity of hydrogen forms of zeolite T of the erionite—offretite type

Abstract

The acidity of H forms of zeolite T obtained by various processes have been determined by treatment with 0.1 mol dm^–3 NaOH and back-titration of the excess and by treatment of the extract obtained by successive batch treatments with 2 mol dm^–3 NaCl. The results of the treatment with NaOH are always higher than those obtained with NaCl. The results of the treatments and chemical analyses have been used to determine the formulae of the unit cells of the H forms and the kind of reaction. The presence of extraskeletal aluminium (AlO⁺), exchangeable with NaCl, and loosely bound silica, soluble in NaOH, has been found. It is postulated that the H forms contain two kinds of acid centre: strong, determinable using NaCl and NaOH, and weak, determinable only using NaOH. The portion of weak centres depends strongly on the method and degree of modification. Identically localized centres have been found to change their strength according to modification conditions.