Microkinetic modeling of CO2 hydrolysis over Zn-(1,4,7,10-tetraazacyclododecane) catalyst based on first principles: Revelation of rate-determining step

Insights into the Relationship of Catalytic Activity and Structure: A Comparison Study of Three Carbonic Anhydrase Mimics

“…The reaction mechanisms of CO 2 hydrolysis by zinctri and zinc-cyclam are similar to that of zinc-cyclen, which has been discussed previously [26]. The entire catalytic reaction cycle is mapped in Scheme 2.…”

“…By correlating the bond dissociation energy of Zn-HCO 3 − , Koziol and co-workers also proposed that bicarbonate release may be the rate-limiting step. However, we found this is not the case for zinc-cyclen, whose rate-limiting step is the adsorption of CO 2 [26]. Koziol et al also calculated the activation energies for the adsorption of CO 2 of these five catalysts in the gas phase at the M06-2X/aug-ccpVTZ//M06-2X/6-311+G(d,p) level of theory.…”

“…The existence of detailed experimental data spurred us to model the catalytic cycle. Recently, our group studied CO 2 catalytic hydrolysis by zinc-cyclen with a combination of density functional theory (DFT) calculations and microkinetic modeling [26]. Our microkinetic model successfully matched experimental data of how the reaction rate constant varies with pH.…”

“…Once a calculated pK a value was obtained, it was compared with an experimental value to justify the accuracy of the selected calculation method. We have previously shown that the BMK/6-311++G** level of theory is very accurate at predicting pK a [26]. The pK a value of zinc-cyclen was calculated to be 7.9, whereas the experimental value was reported to be 8.1.…”

“…Note that Fig. 3 is reproduced here from [26] to facilitate comparison. The first step of the catalytic reaction involves the oxygen atom of 1 nucleophilically attacking the carbon atom of CO 2 and formation of a weakly associated precursor complex (structure 2) via a large barrier (TS1).…”