Santiago-Rodríguez, Yohaselly

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    Analysis of reaction pathways on the catalytic conversion of CO2 using quantum mechanical calculations
    (2015) Santiago-Rodríguez, Yohaselly; Curet-Arana, María C.; College of Engineering; Cardona Martínez, Nelson; Santana, Alberto; Marcelo Suárez, Oscar; Department of Chemical Engineering; Méndez Mella, Héctor
    The greenhouse gas CO2 is an inexpensive and abundant feedstock that may be used to produce valuable organic compounds. The main goal of this work was to unravel reaction pathways for CO2 conversion through hydrogenation on heterogeneous catalysts and through the coupling reaction with ethylene oxide facilitated by homogeneous catalysts. The thermochemistry of several adsorption, decomposition, hydrogenation and oxidation reactions on Au(111) was thoroughly analyzed with density functional theory (DFT). Our results indicate that the production of formic acid, formaldehyde and methanol on Au(111) is not thermodynamically favorable. Cu(111) surfaces doped with Ni, Pd, Ti, Mg, Ga and Al were screened using different descriptors. A systematic study of the thermochemistry for elementary steps in the synthesis of formic acid, formaldehyde and methanol from CO2 and CO were developed to evaluate the performance of Ga/Cu(111), Mg/Cu(111) and Ti/Cu(111) compared to Cu(111). Our results suggest that Ga/Cu(111) and Mg/Cu(111) might be promising catalysts for CO2 and CO hydrogenation. Each of the doped Cu surfaces exhibited different reaction mechanisms for the synthesis of the desired products. Methanol was predicted to be selectively produced from CO2 on Ga/Cu(111) and Mg/Cu(111). DFT methods were also used to analyze metal-salen catalysts in the coupling of CO2 with ethylene oxide. The effect of several metal centers and axial ligands on the reaction energies for the formation of relevant intermediates was investigated. The UOPBE/LANL2DZ and B3LYP/6-311g**/LANL2DZ methods were compared. There were significant differences on the reaction energies estimated with both methods, but they generated similar geometries for the intermediates. The best description of the reaction system was obtained with UOPBE/LANL2DZ. Calculations with dichloromethane as the solvent were performed. The reaction energies for the CO2- epoxide-salen complexes were lower with 4-dimethylaminopyridine (DMAP) as axial ligand than with Cl. The DMAP complexes with Al and Cr were the most stable intermediates with UOPBE/LANL2DZ. Furthermore, CO2 could be activated by DMAP forming a stable CO2-DMAP complex.