Following the hydrothermal crystallisation of zeolites using time-resolved in situ powder neutron diffraction

Abstract

A specially designed hydrothermal cell has been used for the study of the crystallisation of some zeolites from amorphous aluminosilicate gels by time-resolved in situ neutron diffraction. The effect of sodium hydroxide concentration and temperature has been investigated. Following the reactions in situ has allowed the stability of zeolite phases to be monitored directly and efficiently under real reaction conditions. At the lowest sodium hydroxide concentrations used and at the lowest temperature applied (80°C) sodium zeolite A is the favoured product and after a period in excess of 10 h is the sole product. As the sodium hydroxide concentration or temperature is increased the initially formed sodium zeolite A is replaced by hydroxosodalite. At 140°C hydroxosodalite crystallises directly from the amorphous gel. By determining the changing areas of Bragg reflections with time, crystallisation curves can be obtained. The advantages of the in situ powder neutron diffraction technique over analogous X-ray powder diffraction methods are discussed.