Tuning the hematite (110) surface properties to enhance its efficiency in photoelectrochemistry

We present the analysis of the role of the substitutional doping on the electronic structure of Fe2O3– hematite – (110) surface. The presence of a heteroatom in different crystallographic positions in the surface layer of hematite influences the band structure– additional donor or acceptor states appear in the band gap depending on the type and charge of the heteroatom. The modifications play a role in altering the absorption coefficient, however to a minor extent in the visible light range. On the other hand, all investigated substitutions seem advantageous for the oxygen evolution reaction, as for this reaction the vacuum potential is located inside the band gap. Additionally, the differences in partial charges and binding energy suggest that the substitution site can play a role in preferential binding of the reaction intermediates

Insight into the formation of nanostructured MFI sheets and MEL needles driven by molecular recognition

\u3cp\u3e Mesoporous and nanostructured zeolite-Based catalysts experience prolonged lifetimes due to increased mass transfer and reduced micropore obstruction by coke formation as compared to their bulky microporous counterparts. Diquaternary ammonium structure-Directing agents (SDAs) can be used to synthesize hierarchical MFI sheet-Like and MEL needle-Like zeolites. An explanation of the underlying molecular-Level details of the synthesis of these nanostructured zeolites is presented on the basis of non-Covalent interactions between the template and zeolite surfaces as well as silicate oligomers studied by means of classical molecular dynamics. Use was made of Si \u3csub\u3e11\u3c/sub\u3e and Si \u3csub\u3e33\u3c/sub\u3e silicate oligomers that contain structural features of the framework to be formed as originally proposed by the Leuven group. Molecular recognition is driven by a combination of strong electrostatic and weaker dispersion interactions. An analysis of the early stage of zeolite formation is necessary, as the template adsorption energies in the fully formed zeolite crystals cannot explain the preferential growth of the MFI sheets or MEL needles. Specifically, it is found that the differences in dispersion interactions between the SDA alkyl chains and the silicate oligomers are decisive in the formation of particular zeolite structures. \u3c/p\u3

Supported ru metalloporphyrins for electrocatalytic CO\u3csub\u3e2\u3c/sub\u3e conversion

\u3cp\u3eThis paper reports for the first time a computational analysis of the redox properties of graphene-supported Ru-porphyrins as potential catalytic materials for electrochemical CO\u3csub\u3e2\u3c/sub\u3e reduction. Density functional theory reveals that such catalytic ensembles can efficiently activate both CO\u3csub\u3e2\u3c/sub\u3e and CH\u3csub\u3e4\u3c/sub\u3e molecules indicating their generic utility as C\u3csub\u3e1\u3c/sub\u3e-functionalization catalysts. The charge transfer from the graphene surface to the catalytic Ru centers influences the thermodynamic stability of the key reaction intermediates and therefore determines the selectivity of the electrochemical process. The electrochemical reduction of CO\u3csub\u3e2\u3c/sub\u3e can yield CO or methane, depending on the applied potential and reaction conditions. Calculations also identified alternative paths towards methanol and formic acid.\u3c/p\u3

A DFT study of CO2 hydrogenation on faujasite supported Ir4 clusters: on the role of water for selectivity control

Reaction mechanisms for the catalytic hydrogenation of CO2 by faujasite-supported Ir4 clusters were studied by periodic DFT calculations. The reaction can proceed through two alternative paths. The thermodynamically favoured path results in the reduction of CO2 to CO, whereas the other, kinetically preferred channel involves CO2 hydrogenation to formic acid under water-free conditions. Both paths are promoted by catalytic amounts of water confined inside the zeolite micropores with a stronger promotion effect for the reduction path. Co-adsorbed water facilitates the cooperation between the zeolite Brønsted acid sites and Ir4 cluster by opening low-energy reaction channels for CO2 conversion.\u3cbr/\u3

Photoisomerization induced scission of rod-like micelles unravelled with multiscale modeling

\u3cp\u3eHypothesis In photorheological fluids, subtle molecular changes caused by light lead to abrupt macroscopic alterations. Upon UV irradiation of an aqueous cetyltrimethylammonium bromide (CTAB) and trans-ortho-methoxycinnamic acid (trans-OMCA) solution, for instance, the viscosity drops over orders of magnitude. Multiscale modeling allows to elucidate the mechanisms behind these photorheological effects. Experiments We use time-dependent DFT calculations to study the photoisomerization, and a combination of atomistic molecular dynamics (MD) and DFT to probe the influence of both OMCA isomers on the micellar solutions. Findings The time-dependent DFT calculations show that the isomerization pathway occurs in the first triplet excited state with a minimum energy conformation closest to the after photoisomerization predominant cis configuration. In the MD simulations, with sub-microsecond timescales much shorter than the experimental morphological transition, already a clear difference is observed in the packing of the two OMCA isomers: contrary to trans-OMCA, cis-OMCA exposes notable part of its hydrophobic aromatic rings at the micelle surface. This can explain why trans-OMCA adopts rod-like micellar packing (high viscosity) while cis-OMCA spherical micellar packing (low viscosity). Moreover, lowering of the OMCA co-solute concentration allowed us to perform full simulation of the breakup process of the rod-like micelles which are stable prior to isomerization.\u3c/p\u3

TiO 2 -catalyzed synthesis of sugars from formaldehyde in extraterrestrial impacts on the early Earth

\u3cp\u3eRecent synthetic efforts aimed at reconstructing the beginning of life on our planet point at the plausibility of scenarios fueled by extraterrestrial energy sources. In the current work we show that beyond nucleobases the sugar components of the first informational polymers can be synthesized in this way. We demonstrate that a laser-induced high-energy chemistry combined with TiO 2 catalysis readily produces a mixture of pentoses, among them ribose, arabinose and xylose. This chemistry might be highly relevant to the Late Heavy Bombardment period of Earth s history about 4-3.85 billion years ago. In addition, we present an in-depth theoretical analysis of the most challenging step of the reaction pathway, i.e., the TiO 2 -catalyzed dimerization of formaldehyde leading to glycolaldehyde.\u3c/p\u3