Study of small-port and large-port mordenite modifications. Part 1.—Preparation of the HM forms

Abstract

Two procedures for the preparation of HM forms from both small-port mordenite (SPM) and large-port mordenite (LPM) have been studied. The procedures are acid attack of the NaM form and calcination of the NH₄M form. The solids were characterized by chemical analysis, benzene adsorption, X-ray diffraction and precise measurements of the Al Kβ X-ray fluorescence line shifts. The conditions under which SPM can acquire LPM adsorption properties were determined: first, SPHM forms have been proved to exist, thus ruling out the hypothesis of pore blocking by cations; secondly, SPM pore unblocking occurs only when > ca. 20% of Al^IV atoms are extracted from the framework. This result can be achieved either by severe acid attack of SPNaM or calcination of SPNH₄M under deep-bed conditions. In addition, depending on the calcination procedure, the porosity of LPM itself can be blocked by Al^VI species from framework dealumination.