Computational Chemistry Experiment Possibilities

Thanks to a rapid increase in the computational power of modern CPUs, computational methods have become a standard tool for the investigation of physico-chemical phenomena in many areas of chemistry and technology. The area of porous frameworks, such as zeolites, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs), is not different. Computer simulations make it possible, not only to verify the results of the experiments, but even to predict previously inexistent materials that will present the desired experimental properties. Furthermore, computational research of materials provides the tools necessary to obtain fundamental insight into details that are often not accessible to physical experiments. The methodology used in these simulations is quite specific because of the special character of the materials themselves. However, within the field of porous frameworks, density functional theory (DFT) and force fields (FF) are the main actors. These methods form the basis of most computational studies, since they allow the evaluation of the potential energy surface (PES) of the system

Computational Chemistry Experiment Possibilities

Thanks to a rapid increase in the computational power of modern CPUs, computational methods have become a standard tool for the investigation of physico-chemical phenomena in many areas of chemistry and technology. The area of porous frameworks, such as zeolites, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs), is not different. Computer simulations make it possible, not only to verify the results of the experiments, but even to predict previously inexistent materials that will present the desired experimental properties. Furthermore, computational research of materials provides the tools necessary to obtain fundamental insight into details that are often not accessible to physical experiments. The methodology used in these simulations is quite specific because of the special character of the materials themselves. However, within the field of porous frameworks, density functional theory (DFT) and force fields (FF) are the main actors. These methods form the basis of most computational studies, since they allow the evaluation of the potential energy surface (PES) of the system

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

Molecular dynamics study of the silica-water-SDA interactions

In this paper we have applied the molecular dynamics simulations in order to analyse the role of the structure directing tetrapropylammonium ions in the aggregation process that leads to silicalite formation. We address the specific question of how the interactions between silica precursor species and tetrapropylammonium ions/water evolve during the formation of the larger aggregates, that show initial micropore formation from more elementary building blocks. We have followed the dynamics and changes in the position of the tetrapropylammonium ions into the formation of TPA-Si-22 complexes. Moreover, the analysis based on the geometries of the systems being studied as well as the radial distribution function allowed us to predict the location of the TPA cations in fully formed nanoslabs. An interesting result is reported that the template cannot be accommodated any more in the newly formed cavities, but is pushed out of the channel like cavities to positions where in a later stage channel cross sections can be formed

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

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 11 and Si 33 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

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

Dual template synthesis of a highly mesoporous SSZ-13 zeolite with improved stability in the methanol-to-olefins reaction

The dual template synthesis of zeolite SSZ-13 by use of trimethyl-adamantanammonium hydroxide and a diquaternary-ammonium mesoporogen induces considerable mesoporosity without impeding zeolite microporosity. The strongly improved accessibility of Brønsted sites in mesoporous SSZ-13 increases its stability during application as an acid catalyst in the methanol-to-olefins reaction.status: publishe

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