Abstract
The conversion mechanisms of CO2 and H2 in methanol to dimethoxymethane catalyzed jointly by metallic [P3Co-H]+ catalyst and acidic HNTf2 cocatalyst in a domino sequence were investigated at the M06L-SCRF level of density functional theory. The whole conversion has the steps of the Co-catalyzed hydrogenation (CO2 + H2 = HCOOH; HCOOCH3 + H2 = CH3OCH2OH) and acid-catalyzed esterification (HCOOH + CH3OH = HCOOCH3 + H2O; CH3OCH2OH + CH3OH = CH3OCH2OCH3 + H2O) reactions. The full Gibbs free energy profiles show that the bidentate formate complex κ2-[P3Co-OCHO]+ is the resting state and methylating CH3OCH2OH with CH3-NTf2 is the rate-determining step. The whole reaction kinetics is controlled by both [P3Co-H]+ and HNTf2 cocatalyst. Our study clearly shows the individual role of metal catalyst and acid cocatalyst and the need to combine both catalysts for this reaction and explains rationally why this process needs CO2 + H2 + CH3OH rather than only CO2 + H2. Compared to HNTf2 as a cocatalyst, the lower activity of p-TsOH is due to the weaker interaction between acid and substrate. A mechanism for the chain growth and termination of oxymethylene ether is proposed.
Published Version
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