Both thermal and catalytic decomposition of PP sample is studied to understand the effect of catalyst (Al-MCM-41) on the decomposition behaviour. Mesoporous catalyst (Al-MCM-41) is synthesized by sol-gel methods and characterized by X-ray diffraction (XRD) analysis and nitrogen adsorption study. The optimum catalyst composition is found to be around 18.5 wt%, where the reduction in maximum decomposition temperature is around 103 degrees C. The nonlinear Vyazovkin model-free technique is applied to evaluate the quantitative information on variation of E-alpha with alpha for PP sample under both catalytic and noncatalytic nonisothermal conditions. The constant pattern behaviour of the TG curves and the similar trend on variation of E-alpha with alpha for both catalytic and noncatalytic decomposition of PP indicates similar mechanism involved during decomposition. The only effect of catalyst is observed in the form of reduction of the temperature and the activation energy. The literature reported data on such variation are compared with the results of the present study. Results show that Al-MCM-41 is superior to the ZSM-5 catalyst in terms of catalyst loading due to the existence of larger external macropore and mesopore surface in it.(c) 2007 Elsevier B.V All rights reserved.