In this work, a study of the degradation of PE and an EVA copolymer under air atmosphere, in the presence and absence of mesoporous MCM-41, was carried out using thermogravimetric analysis (TGA), focusing on the analysis of the EVA behaviour during this the process. The results obtained show that the air atmosphere causes an increase of the complexity of the process, with respect to the thermal and catalytic pyrolysis in N 2 atmosphere, exhibiting more decomposition steps. The results obtained for both polymers show that the presence of MCM-41 does not practically affect the temperature of the oxidative decomposition processes, but a clear effect has been found on the main step of degradation, that supports the existence of cracking or incomplete oxidation reactions, and clearly it enhances the carbonaceous residue formation.