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DFT methods were used to analyze metal (M)-doped Cu(111) surfaces to identify surface alloys that could catalyze the hydrogenation of CO2. The adsorption of relevant species for CO2/CO hydrogenation were studied on Cu(111) surfaces doped with Ga, Mg, and Ti. Preferred adsorption sites, geometries, and binding energies for relevant intermediates were determined. A systematic study of the thermochemistry of plausible surface reactions for CO2/CO hydrogenation on Ga/Cu(111), Mg/Cu(111), and Ti/Cu(111) was performed to postulate reaction mechanisms for the synthesis of formic acid, formaldehyde, and methanol. Our results suggest that Ga/Cu(111) and Mg/Cu(111) surfaces might be promising catalysts for the synthesis of methanol from CO2 hydrogenation. CO2 is activated by chemisorption on Mg/Cu(111) and Ti/Cu(111), but the latter surface has a strong interaction with O, which inhibits the last reaction steps and the desorption of the products. Our results demonstrate that the thermochemistry of CO2 hydrogenation for the synthesis of the different products varies drastically depending on the dopant on Cu(111). Furthermore, our results suggest that the formation energies of HCOO, CH2O, CH3O, and HCO are good descriptors for catalyst screening.

Calcium sulfide (CaS) nanoparticles are cadmium free fluorescent nanostructures with potential applications in nanomedicine and photovoltaic cells. We report on the synthesis and optical properties of CaS nanoparticles prepared by the reaction of Ca(CH3CO2)2 and DMSO in a microwave. The absorption spectra of CaS prepared from this method consists of a well-defined peak in the UV and a long wavelength tail that extends above 700 nm. Emission bands centered at around 500 nm with a long wavelength tail that extends above 600 nm are observed upon excitation at 405 nm. STM measurements reveal the formation of CaS nanoparticles with an average diameter of (3.2 ± 0.7) nm. The direct and indirect band gaps are estimated to be (0.403 ± 0.003) eV and (4.135 ± 0.006) eV, respectively. Theoretical calculations on small CaS clusters are used to establish the physical properties of calcium sulfide nanoclusters, including the optical absorption spectra. Unique to CaS nanostructures is the absorption of light at wavelengths longer that in the bulk material instead of the blue shift associated with quantum confinement effects in semiconductors. Indeed, the strong absorption bands in the visible region of the spectra of the CaS nanostructures do not have a counterpart in the gas or solid phases. The optical absorption spectra are proposed to have a significant contribution from indirect transitions which are discussed in terms of the dispersion of the phonon frequency.

Quantum mechanical study of the reaction of CO 2 and ethylene oxide catalyzed by metal-salen complexes: effect of the metal center and the axial ligand Abstract Density functional theory calculations were used to evaluate the thermochemistry of plausible elementary steps for the reaction of CO 2 with ethylene oxide catalyzed by metal-salen complexes consisting of Co, Cr, Mn, Fe, Al and Zn. The effect of the axial ligands on the energies of reaction was studied using chlorine and 4-dimethylaminopyridine (DMAP). This analysis was performed using UOPBE/LANL2DZ to screen the plausible reaction intermediates. The most favorable intermediates were then studied with B3LYP/6-311 g**/LANL2DZ in gas phase and in dichloromethane to evaluate the method and solvent effect on their reaction energies and geometries. Our results demonstrated that when chlorine is the axial ligand, the formation of CO 2 -epoxide-salen complexes was an endothermic reaction for all metal-salen complexes considered. However, the energies of reaction decreased for these complexes with DMAP as axial ligand. While differences were found in the reaction energies with the two methods, both methods yield similar minimum energy structures on the intermediates that were analyzed. The most energetically favorable intermediates for the coupling of CO 2 and ethylene oxide obtained when the solvent was taken into account were the complexes with Al as metal center and DMAP as axial ligand. However, the inclusion of dichloromethane as a solvent did not have a significant effect in the reaction energies compared to the vacuum system. Our results indicated that the axial ligand impacts the electronic properties of the catalyst, such as the HOMO and LUMO surfaces, Electronic supplementary material The online version of this article (