| Abstract
| - In this work, quantum chemical methods were used to study propane conversion reactions on zeolites; thesereactions included protolytic cracking, primary hydrogen exchange, secondary hydrogen exchange, anddehydrogenation reactions. The reactants, products, and transition-state structures were optimized at the B3LYP/6-31G* level and the energies were calculated with CBS-QB3, a complete basis set composite energy method.The computed activation barriers were 62.1 and 62.6 kcal/mol for protolytic cracking through two differenttransition states, 30.4 kcal/mol for primary hydrogen exchange, 29.8 kcal/mol for secondary hydrogen exchange,and 76.7 kcal/mol for dehydrogenation reactions. The effects of basis set for the geometry optimization andzeolite acidity on the reaction barriers were also investigated. Adding extra polarization and diffuse functionsfor the geometry optimization did not affect the activation barriers obtained with the composite energy method.The largest difference in calculated activation barriers is within 1 kcal/mol. Reaction activation barriers dochange as zeolite acidity changes, however. Linear relationships were found between activation barriers andzeolite deprotonation energies. Analytical expressions for each reaction were proposed so that accurate activationbarriers can be obtained when using different zeolites as catalysts, as long as the deprotonation energies arefirst acquired.
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