Improving the activity of gold nanoparticles for the water-gas shift reaction using TiO2-Y2O3: an example of catalyst design.

In the last ten years, there has been an acceleration in the pace at which new catalysts for the water-gas shift reaction are designed and synthesized. Pt-based catalysts remain the best solution when only activity is considered. However, cost, operation temperature, and deactivation phenomena are important variables when these catalysts are scaled in industry. Here, a new catalyst, Au/TiO2-Y2O3, is presented as an alternative to the less selective Pt/oxide systems. Experimental and theoretical techniques are combined to design, synthesize, characterize and analyze the performance of this system. The mixed oxide demonstrates a synergistic effect, improving the activity of the catalyst not only at large-to-medium temperatures but also at low temperatures. This effect is related to the homogeneous dispersion of the vacancies that act both as nucleation centers for smaller and more active gold nanoparticles and as dissociation sites for water molecules. The calculated reaction path points to carboxyl formation as the rate-limiting step with an activation energy of 6.9 kcal mol-1, which is in quantitative agreement with experimental measurements and, to the best of our knowledge, it is the lowest activation energy reported for the water-gas shift reaction. This discovery demonstrates the importance of combining experimental and theoretical techniques to model and understand catalytic processes and opens the door to new improvements to reduce the operating temperature and the deactivation of the catalyst.

Ag2S Quantum Dot-Sensitized Solar Cells by First Principles: The Effect of Capping Ligands and Linkers.

Quantum dots solar cells, QDSCs, are one of the candidates for being a reliable alternative to fossil fuels. However, the well-studied CdSe and CdTe-based QDSCs present a variety of issues for their use in consumer-goods applications. Silver sulfide, Ag2S, is a promising material, but poor efficiency has been reported for QDSCs based on this compound. The potential influence of each component of QDSCs is critical and key for the development of more efficient devices based on Ag2S. In this work, density functional theory calculations were performed to study the nature of the optoelectronic properties for an anatase-TiO2(101) surface sensitized with different silver sulfide nanoclusters. We demonstrated how it is possible to deeply tune of its electronic properties by modifying the capping ligands and linkers to the surface. Finally, an analysis of the electron injection mechanism for this system is presented.

Adsorption of Prototypical Asphaltenes on Silica: First-Principles DFT Simulations Including Dispersion Corrections.

In this work, we explore the interaction between some prototypical asphaltene and porphyrin molecules with a fully hydroxylated (0001) surface of α-quartz by means of theoretical calculations based on the density functional theory (DFT) under periodic boundary conditions. The influence of dispersion forces, adsorption geometries, and size of the side chain is analyzed. The inclusion of London dispersion forces is overriding as they increase the interaction by about 1 order of magnitude. All of the considered molecules strongly interact with the hydroxylated surface and prefer to adsorb in a parallel position instead of vertically. It is also found that adsorption energy always increases with larger side chains because dispersion interactions also augment. Interestingly, in the case of porphyrin, the less stable isomer in the gas phase is the preferred one after adsorption, which is substantiated by a differential stabilization induced by the surface. Finally, we present a comparative study of the adsorption of these model molecules in terms of energy per area unit and energy per interacting π electron.