Methane activation over molybdenum disulfide, molybdenum carbide, and silver(110). Molecular orbital theory

The atom superposition and electron delocalization molecular orbital (ASED-MO) theory is used to study methane C-H bond activation over MoS{dollar}sb2{dollar}, MoC, and O/Ag(110), C{dollar}sb1{dollar} coupling mechanisms to form C{dollar}sb2{dollar}H{dollar}sb6{dollar} and C{dollar}sb2{dollar}H{dollar}sb5{dollar}OH on MoS{dollar}sb2{dollar}, CH{dollar}sb2{dollar} coupling on MoC, and the binding properties of C{dollar}sb2{dollar} olefins to 2 S in the CpMoS{dollar}sb4{dollar}MoCp (Cp = C{dollar}sb5{dollar}H{dollar}sb5{dollar}) complex and on MoS{dollar}sb2{dollar}.; For methane C-H bond activation by the Mo{dollar}sp{lcub}rm IV{rcub}{dollar} oxidative insertion mechanism, the theory predicts low barriers for both MoS{dollar}sb2{dollar} and MoC catalysts. These results suggest the possibility of incorporating methane into the Fischer-Tropsch process over these catalysts. The activation barrier for H abstraction by O on Ag(110) is calculated to be lower than over most oxides. The calculations also suggest the possibility of direct O insertion into a methane C-H bond to make methanol on the O/Ag(110) surface.; It has been demonstrated by Klier and coworkers that the Fischer-Tropsch reaction over MoS{dollar}sb2{dollar} proceeds by the CO insertion mechanism. The calculations also favor this mechanism. High barriers are found for the other C{dollar}sb1{dollar} coupling mechanisms (CH{dollar}sb3{dollar} + CH{dollar}sb3{dollar}, CH{dollar}sb2{dollar} + CH{dollar}sb3{dollar}, and CH{dollar}sb2{dollar} + CH{dollar}sb2{dollar}). Two CH{dollar}sb2{dollar} coupling on MoC is also studied. The calculations show that the coupling barrier on MoC is smaller than that on MoS{dollar}sb2{dollar} and the desorption of C{dollar}sb2{dollar}H{dollar}sb4{dollar} is calculated to be easier on MoC.; Complexes which have a S{dollar}sb4{dollar} structure chelated by ligands (e.g. C{dollar}sb2{dollar}H{dollar}sb4{dollar} and C{dollar}sb2{dollar}H{dollar}sb2{dollar}) have been insolated by DuBois and coworkers. Acetylene hydrogenation in these complexes were also observed. These seem to suggest that S{dollar}sp{lcub}2-{rcub}{dollar} in MoS{dollar}sb2{dollar} basal planes would possibly have the same reactivities. This would be in contrast to the general belief that MoS{dollar}sb2{dollar} basal planes are inert toward catalytic reactions and that hydrogenation over MoS{dollar}sb2{dollar} occurs on the edge unsaturated Mo{dollar}sp{lcub}rm IV{rcub}{dollar} sites. Theoretical calculations carried out to study the binding strengths of C{dollar}sb2{dollar} olefins to the sulfur anions in the CpMoS{dollar}sb4{dollar}MoCp complex and on MoS{dollar}sb2{dollar} demonstrate that the binding of C{dollar}sb2{dollar} olefins to MoS{dollar}sb2{dollar} basal plane S{dollar}sp{lcub}2-{rcub}{dollar} is much weaker than in the complex.