Non-isothermal kinetic studies of the template decomposition from silicalite-1 framework-high temperature X-ray diffraction and thermogravimetric analysis

Abstract

Non-isothermal decomposition of the tetrapropylammonium cations (TPA +) intercalated in silicalite-1 framework has been carried out using thermogravimetric (TG) analysis and high temperature powder X-ray diffraction (HTXRD) techniques. Conversion factor for template decomposition is calculated using two methods viz., % weight loss from the thermogravimetric analysis and changes in the intensities of the Bragg reflections 101/011 and 200/020 in the HTXRD patterns scanned at different temperatures (range 298–823 K). The calculated apparent activation energy for template decomposition in air was 129 and 125 kJ mol −1, respectively, for the two techniques TG and HTXRD, calculated using the Kissinger method. By Flynn–Wall–Ozawa approach of isoconversion, apparent activation energy for template decomposition in air was 123 and 124 kJ mol −1, respectively, for TG and HTXRD data. The reaction order was determined using the method of Kennedy and Clark and it is ∼2 by both the techniques. The second order of template decomposition can be attributed to the fact that TPA + is positioned in two different orientations inside the silicalite-1 framework. Template removal occurs with a contraction in unit cell dimensions. There is a decrease in the lattice parameters of the as-synthesized silicalite-1 sample after removal of template from the framework.