We describe the application of transition path sampling methods to the methanol coupling reaction in the zeolite chabazite; these methods have only been recently applied to complex chemical systems. Using these methods, we have found a new mechanism for the formation of the first C-C bond. In our mechanism, the reaction, at 400 degrees C, proceeds via a two-step process: (1) the breaking of the C-O bond of the chemisorbed methoxonium cation, followed by the transfer of a hydride ion from the remaining methanol molecule to the methyl cation, resulting in the formation of H2O, CH4, and CH2OH+ and (2) a simultaneous proton transfer from methane to water, and direct C-C bond formation between the methyl anion and CH2OH+, resulting in the formation of ethanol. The C-C bond forming process has the higher barrier, with an activation energy of about 100.49 kJ/mol. (c) 2005 Elsevier B.V. All rights reserved.