Conversion of CH4 to CH3OH: Reactions of CoO+ with CH4 and D2, Co+ with CH3OD and D2O, and Co+(CH3OD) with Xe

Abstract

The mechanisms and energetics involved in the conversion of CH{sub 4} to CH{sub 3}OH by CoO{sup +} are examined by using guided ion beam mass spectrometry. The forward and reverse reactions, CO{sup +} + CH{sub 4} CO{sup +} + Ch{sub 3}OH, the collisional activation of Co{sup +}(CH{sub 3}OH), and the related reactions, CoO{sup +} + D{sub 2} Co{sup +} + D{sub 2}O, are studied. It is found that the oxidations of methane and D{sub 2} by CoO{sup +}, both exothermic reactions, do not occur until overcoming activation barriers of 0.56 x 0.08 and 0.75 x 0.04 eV, respectively. The behavior of the forward and reverse reactions in both systems is consistent with reactions that proceed via the insertion intermediates R-Co{sup +}-OH, where R = CH{sub 3} or H. The barrier is probably attributable to a four-centered transition state associated with addition of RH across the CoO{sup +} bond. In the Co{sup +} + CH{sub 3}OH system (where CH{sub 3}OD labeled reactant is used), reactions explained by initial C-H and O-H activation are also observed. The reaction mechanisms and potential energy surfaces for these systems are derived and discussed. Phase space theory calculations are used to help verify these details formore » the CoO{sup +} + D{sub 2} system. Thermochemistry for several species including CoOH{sup +}, CoD{sup +}, CoH, CoCH{sub 3}{sup +}, Co{sup +}(CH{sub 3}OD), CoOCH{sub 3}{sup +}, and possibly OCoCH{sub 3}{sup +} is derived from measurements of reaction thresholds. 59 refs., 8 figs., 4 tabs.« less