Ab initio methods are used to study the transition state structures and activation energies of ethane cracking, hydrogen exchange, and dehydrogenation reactions catalyzed by a zeolite model cluster. The reactant and transition state structures are optimized by HF and MP2 methods and the final energies are calculated using a complete basis set composite energy method. The computed activation barriers are 71.39 kcal/mol for cracking, 31.39 kcal/mol for hydrogen exchange and 75.95 kcal/mol for dehydrogenation using geometries optimized with the MP2 method. The effects of cluster size and acidity on the reaction barriers are also investigated. The relationships between activation barriers and zeolite deprotonation energies for each reaction are proposed so that accurate activation energies can be obtained when using different zeolites as catalysts. (C) 2004 Elsevier B.V. All rights reserved.