Isopropylation of toluene: a comparative study of microporous zeolites and mesoporous MCM-41 materials Original Research Article

Al-MCM-41, zinc and iron containing Al-MCM-41 molecular sieves with Si/M (M = Al, Zn and Fe) ratios of 50 and 100 were hydrothermally synthesised. The above synthesised materials as well as commercial zeolites β, mordenite and ZSM-5, were characterised systematically by various analytical and spectroscopical techniques. The structure and crystallinity of synthesised materials as well as commercial zeolites were confirmed by X-ray diffraction (XRD). The textural properties were measured by nitrogen adsorption studies. 29Si magic angle-spinning (MAS) NMR and 27Al MAS NMR experiments reveal that all the MCM-41 samples contain a small amount of aluminium-rich extra-framework species both inside and outside the mesoporous samples after calcination. The diffuse reflectance spectroscopy (DRS) and electron paramagnetic resonance (EPR) spectroscopy studies confirm the co-ordination environment of Fe in Al-MCM-41 framework. The acidity of the catalysts was analyzed by TPD of NH3 and by pyridine adsorbed FT-IR spectroscopy. Vapour phase isopropylation of toluene with isopropyl acetate (IPA) was carried out over mesoporous and microporous catalysts in the temperature range of 200–275 °C. The effects of feed ratio, toluene space velocity and reaction temperature were studied and the results are discussed. Conditions were optimised to get better toluene conversion and better selectivity to para-cymene (p-cymene), an important product.