Electrocatalytic carbon dioxide activation: the rate-determining step of pyridinium-catalyzed CO2 reduction.

The reactivity of reduced pyridinium with CO(2) was investigated as a function of catalyst concentration, temperature, and pressure at platinum electrodes. Concentration experiments show that the catalytic current measured by cyclic voltammetry increases linearly with pyridinium and CO(2) concentrations; this indicates that the rate-determining step is first order in both. The formation of a carbamate intermediate is supported by the data presented. Increased electron density at the pyridyl nitrogen upon reduction, as calculated by DFT, favors a Lewis acid/base interaction between the nitrogen and the CO(2). The rate of the known side reaction, pyridinium coupling to form hydrogen, does not vary over the temperature range investigated and had a rate constant of 2.5 M(-1)  s(-1). CO(2) reduction followed Arrhenius behavior and the activation energy determined by electrochemical simulation was (69±10) kJ mol(-1).

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