Carbonic Acid Formation from Reaction of Carbon Dioxide and Water Coordinated to Al(OH)3: A Quantum Chemical Study

Density functional and ab initio calculations have been performed on CO2-nH(2)O and Al(OH)(3)-CO2-nH(2)O (where n = 1, 2, 3) cluster models to elucidate the catalytic effect of a hydroxylated metal center on the formation of carbonic acid (H2CO3). B3LYP/6-311++G(d,p)-calculated geometries and RI-SCS-MP2/augcc-pVTZ//B3LYP/6-311++G(d,p)-calculated energies with respect to isolated gas-phase molecules and various H2O, CO2, and H2CO3-Al(OH)(3) complexes are presented. It is shown here that H2CO3 formation proceeds via direct CO2 and nH(2)O reaction with very high activation barriers in the gas phase, 51.40, 29.64, and 19.84 kcal/mol for CO2-H2O, CO2-2H(2)O, and CO2-3H(2)O clusters, respectively, decreasing in magnitude with an increase in the number of H2O molecules. The energetics as well as the reaction mechanism and energy landscape change significantly when carbonic acid is formed from CO2 and nH(2)O in the presence of Al(OH)(3), a hydroxylated metal center. Results presented here show important details of the influence of the coordinating metal center in the formation of H2CO3.