An in situ calorimetric study of zeolite crystallization kinetics

In this in situ calorimetric method the reaction rate is derived from the rate of evolution of the heat of reaction. The rationale and the procedure to obtain the reaction rate from the recorded heat flow during crystallization are elucidated. One major advantage of this method is the continuous and accurate measurement of crystallization rates over a wide range of crystallinity, In contrast, other methods like XRD and microscopy, directly measure the mass (or volume) of the product, but not the reaction rate, at a few times and only an average crystallization rate is usually computed. Other features of the in situ calorimetric method are also discussed. A case study of the crystallization kinetics of FAU zeolite is reported. The Arrhenius activation energy for crystallization increases from 66 +/- 2.3 to 72 +/- 0.8 kJ/mol as the crystallization proceeds from similar to5% to similar to75%. This change can be correlated to the increase of the Si/Al ratio in the solution, indicating that Al-rich aluminosilicate nutrient species are more reactive in the crystal growth. (C) 2002 Elsevier Science B.V. All rights reserved.