using FTIR studies for reactions carried out at 373-773 K. It was found in our calculations that free energy barrier for the reaction is lower in the case of H-ZSM-5 than that of H-MCM-22. One way to understand this difference is by the difference in the acidic strengths of zeolites. We find a difference in the stretching frequency of the O-H bond in both the zeolites (see Figure ), indicating that H-ZSM-5