Aggregation and the Siginificant Difference in Reactivity therein: Blocking the CO2-to-CH3OH Reaction Pathway

• A CoPc/CNT system was recently reported to transform CO2 to methanol via electrochemical reductions, despite the catalyst has been studied since the 1980s, such observations were not reported earlier. A clue to the high methanol selectivity is that CoPc exist as mainly as monomers in the new report while in earlier works CoPc aggregates dominate. Here we have studied the reactivity of monomeric and dimeric CoPc by DFT. The mechanism involves rate limiting CO2 association, with the C-O cleavage step being having very similar activation free energy. Once the Co-CO- intermediate is formed the reaction bifurcates with two possible paths, CO dissociation or further reduction and protonation to give the Co-CHO- intermediate, which then leads to methanol by further reactions. For the monomeric species at low reduction potentials CO dissociation is favored, but the formation of Co-CHO- becomes competitive at more negative applied potentials. For the dimer the CO dissociation is always favored, and the reduction needed to form the C-H bond is negative enough for it not to be observed. The more difficult reduction stems from repulsive interac- tions between the Co-Pc units and lower solvent stabilization of the charge in the aggregate.

Ämnesord

NATURVETENSKAP  -- Kemi -- Teoretisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Theoretical Chemistry (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

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