The influence of heating rate on template removal in silicalite-1: An in situ HT-XRPD study

The effect of heating rate on thermal behavior of TPA-silicalite-1 during calcination and the reaction kinetics for TPA decomposition were investigated. The cell parameters of the TPA-silicalite-1 during the heating cycles were determined with the aid of high temperature X-ray diffraction data and the Rietveld method. The template decomposition is accompanied by a large contraction of the unit cell. The unit cell dimensions during template removal are not affected significantly by the heating rate. Consequently, the rate of contraction is approximately proportional to the heating rate. The intensity of some diffraction peaks changes during heating, especially the 101/011 and the 200/020 peaks. The intensity change of those peaks shows the same dependence with temperature as the TPA occupancy, indicating that these parameters are related. An analysis of the kinetics for TPA decomposition based on the intensity change of the 101/011 and the 200/020 peaks was performed. The apparent activation energy (Ea) of the template decomposition in silicalite-1 determined with the Kissinger and the Flynn–Wall–Ozawa methods was 138 (±25) and 138 (±29) kJ mol−1, respectively. The reaction order, determined with the method of Kennedy and Clark, was close to 0.5 indicating that the rate-limiting step is mono-dimensional diffusion. Ea was 140 (±30) kJ mol−1, in good agreement with the results obtained with the other methods.