Dehydration of the zeolite merlinoite from the Khibiny massif, Russia: an in situ temperature-dependent single-crystal X-ray study

摘要

Dehydration behaviour of the zeolite merlinoite, NaK_(11)[Al_(12)Si_(20)O_(64)]·15H_2O, from the Khibiny massif (Russia) was studied by means of single-crystal X-ray diffraction conjoined with step-wise heating to 225 ℃. At room temperature merlinoite has the space group Immm with a = 14.0312(5), b = 14.2675(6), c = 10.0874(4) A ° , and V = 2019.40(14) A ° ~3. At 75 ℃ the merlinoite structure undergoes pronounced dehydration accompanied by a phase transition to a structure that has the space group P4_2mc and remains consistent at elevated temperature. A fully dehydrated phase occurs at 200 ℃ (at 225 ℃: a = 13.341(4), b = 13.341(4), c = 9.707(4)A ° , V = 1727.7(12)A ° ~3). Dehydration-induced framework distortion and symmetry were found to be different from those observed for synthetic potassium merlinoite with the K_(11.5)[Al_(11.5)Si_(20.5)O_(64)]·15H_2O composition.