Studies on the Microscopic Kinetics of the Dehydrogenation for Methanol

The 1,1 dehydrogenation reaction of methanol was investigated by ab initio MO calculations using RHF/4-31G basis set. The energy gradient method was used to optimize the equilibrium geometries of the reactant, the transition state and the product. The activation energy and reaction heat were calculated to be 454.2 kJ·mol^-1 and 365.2kJ·mol^-1, respectively. The results indicate that the 1,1 dehydrogenation path of methanol is favourable to occur than the 1,2 path in terms of activation energy and entropy factors but unfavourable in terms of reaction heat. The reaction ergodography was analyzed by means of intrinsic reaction coordinate （IRC） method. The changes of some physical properties along IRC were followed and the results indicate that the stretching of the two CH bonds are not in step with each other in the process of the 1,1 dehydrogenation reaction. The vibrational analyses of the reactant, transition state and the reaction coordinate were carried out by the numerial differentiation method and the vibrational frequency correlation diagram was made and found that the CO and OH stretching vibrations are adiabatic while the symmtical stretching vibration of CH bonds which are approximately in the direction of the IRC at the early stage of the reaction are important to the mode selectivity of the 1,1 dehydrogenation reaction of methanol.