Metal oxides and hydroxides are known to form carbonates and bicarbonates through reacting with gas-phase CO2. These reactions may be useful for carbon capture from flue or fuel gas streams if systems having both favorable thermodynamics and kinetics can be identified or engineered, through doping or mixing with other compounds. Experimental screening of many different systems is time consuming and expensive. First-principles prediction of the thermodynamics of novel systems could be a powerful tool to help narrow the experimental search space. Density functional theory (DFT) is a relatively efficient tool for computing the thermodynamics of crystalline systems. However, previous studies with DFT have shown that common generalized gradient approximation (GGA) functionals are not sufficiently accurate for predicting the thermodynamics of CO2 reacting with metal oxides or hydroxides.  We have therefore tested the accuracy of several different exchange-correlation functionals (PW91, PBE, PBEsol, TPSS, and revTPSS) for computing the thermodynamic properties of CO2 reactions with selected transition metal oxides TMO and hydroxides TM(OH)2 where TM = Mn, Ni, Zn, Cd. We have used lattice dynamics to compute the finite-temperature free energies of these systems. We have computed the van't Hoff plots, describing the reaction equilibrium as a function of the partial pressures of CO2 and H2O and the temperature. Among all the functionals we tested, PBEsol generally predicts better agreement of the van't Hoff plots with data from experimentally-based thermodynamic correlations. In contrast, the formation enthalpies for the compounds are predicted with higher accuracy with TPSS and revTPSS functionals than the other three functionals. Hence, the better performance of the PBEsol functional is due to a partial cancellation of errors. Finally, we present our predictions for all CO2 capture reactions that lie on the Gibbs free energy convex hull as a function of temperature and the partial pressures of CO2 and H2O.

Thermodynamic predictions of carbonate reactions: How good is DFT?

241st National Meeting (2011)

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