A computational study of methane catalytic reactions on zeolites

The cluster approach method is used to study the transition state structures and the activation barriers of methane hydrogen exchange and dehydrogenation reactions catalyzed by zeolites. The reactant and transition state structures are optimized at the B3LYP/6-31g* level, and the energies are calculated using CBS-QB3, a complete basis set composite energy method. The computed activation barriers are 33.53 kcal/mol for the hydrogen exchange reaction and 90.08 kcal/mol for the dehydrogenation reaction. The effects of zeolite acidity on the reaction barriers are also investigated by changing the length of the terminal SiH bonds. Analytical expressions between activation barriers and zeolite deprotonation energies for each reaction are proposed so accurate activation barriers can be obtained when using different zeolites as catalysts. Additionally, transition state theory is applied to estimate the reaction rate constants of the hydrogen exchange and dehydrogenation reactions from calculated activation barriers, and vibrational, rotational and translational partition functions.

In this work, zeolite catalyzed methane hydrogen exchange and dehydrogenation reactions are investigated using Density Functional Theory and ab initio methods. Applying the cluster approach method, the activation barriers for each reaction are calculated and the reaction rate constants are estimated using Transition State Theory. Additionally, zeolite acidity effects on activation barriers are discussed. We find good agreement with experimental results and can also extrapolate the results to other zeolites using the zeolite acidity effect. Figure optionsDownload as PowerPoint slide