DENSITY-FUNCTIONAL THEORY CALCULATIONS OF THE TRANSITION-STATES FOR HYDROGEN-EXCHANGE AND DEHYDROGENATION OF METHANE BY A BRONSTED ZEOLITICPROTON

Density functional and semiempirical (MNDO) theories are used to deter mine transition states and the corresponding activation barriers of hy drogen exchange and dehydrogenation of methane catalyzed by a protonat ed zeolite cluster model. The nonlocal density functional activation b arriers were found to be 125 and 343 kJ/mol for hydrogen exchange and dehydrogenation, respectively. From the imaginary frequency of one of the transition state eigenmodes, the reaction coordinates were deduced . Additionally, from the activation barrier and vibration, rotation, a nd translation partition functions, reaction rate constants have been evaluated using transition state reaction rate theory.