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The Journal of Physical Chemistry C
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Item-typ:Veröffentlichung, HCHO Sensing Mechanism of In4Sn3O12 Revealed by DRIFTS and DFT(American Chemical Society, 2023-05-25); ; ; ; The combination of operando Diffuse Reflectance Infrared Fourier Transform Spectroscopy measurement and Density Functional Theory calculation reveals the counterintuitive HCHO sensing mechanism of In4Sn3O12. It is merely partial oxidation of HCHO into formate (or HCOOH) with medium activation energy (0.43–0.68 eV) and sufficient electron donation effect that is responsible for the sensor signal at the optimum temperature of 200 °C. The Sn (3a)-connected O is the active site and plays key roles in both HCHO adsorption and partial oxidation.Wissenschaftlicher ArtikelBand:127Heft:2249 69 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, NO Degradation on the Anatase TiO2 (001) Surface in the Presence of Water(American Chemical Society, 2022-10-10); ; ; ; Nitric oxide (NO) is known to degrade to nitric acid (HNO3) on anatase TiO2 facets under visible light irradiation in the presence of water. However, the exact role that water plays in this photoreaction is not fully understood. By employing the density functional theory (DFT) and time-dependent density functional tight binding (TD-DFTB), we show the viability of two suggested degradation pathways involving water. Both reaction pathways are triggered by a charge transfer excitation from the NO molecule to the TiO2 surface. In one of them, NO interacts with dissociated water molecules adsorbed on the surface to form HONO+, whereas for the second pathway, NO is oxidized to NO2+ by capturing one oxygen atom from the substrate. Both HONO and NO2 are known byproducts in the photodegradation of NO, which further react with adsorbed water to finally produce HNO3. We also demonstrate by means of nudged elastic band calculations that these reactions are unlikely to happen without illumination.Wissenschaftlicher ArtikelBand:126Heft:4183 48 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Thermal Activation of Nanoporous Gold for Carbon Monoxide OxidationHeterogeneous catalysts based on gold have attracted considerable attention over the last 30 years. In spite of its chemical inertness, the research on gold catalysis has proven that in oxidation reactions, for instance, high activities and, in particular, selectivities can be achieved. While mostly Au nanoparticles supported on suitable oxides have been focused on in the literature, more recently, nanoporous gold (npAu) was found to be an alternative that shows similarly good catalytic performance, even though the characteristic structural length (diameter of ligaments vs particle diameter) is an order of magnitude larger. To date, however, no recipe has been reported to reliably activate npAu for total oxidations, such as CO oxidation. Here, we present such an activation procedure that allows obtaining high conversion levels on the time scale of an hour, independently of the prehistory of the samples. It consists of one or several steps where the catalyst is subjected to a thermal treatment in the reaction mixture (CO + O2) at 300 °C for 1 min only. Previously, it was assumed that such a high-temperature treatment would result in coarsening of the nanoporous structure and thus in an intolerable loss of surface area. According to our results, however, short annealing steps hardly alter the ligament size but effectively remove residuals from the preparation and/or modify the surface chemistry so that a catalytically active state is obtained quickly. Reproducibly, rates can be achieved, which are in good agreement with values previously reported in the literature and are stable for at least several days on stream. Our results open the way for a practical use of npAu as well as for further studies on the mechanistic origin of its catalytic activity.Wissenschaftlicher ArtikelBand:126Heft:424 24 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Fluoride Anions in All-Silica Zeolites: Studying Preferred Fluoride Sites and Dynamic Disorder with Density Functional Theory CalculationsIn all-silica zeolites synthesized via the “fluoride route”, the fluoride anions are typically incorporated in small cages, forming [SiO4F]− trigonal bipyramids. While diffraction and NMR experiments can elucidate the fluoride location(s) and the occurrence/absence of dynamic disorder, they provide limited insights into the factors that determine equilibrium position and dynamic behavior. To develop a more thorough understanding, electronic structure calculations in the framework of dispersion-corrected density functional theory (DFT) were performed for five all-silica zeolites (NON, STF, IFR, STT, and CHA frameworks). DFT-based predictions of the energetically preferred fluoride location within a given cage were mostly in excellent agreement with experiment. Apart from the known tendency of fluoride anions to be located close to small rings, there are no easily generalizable crystal-chemical rules to predict the most probable fluoride sites. DFT-based molecular dynamics calculations were employed to predict and explain the dynamic behavior of the fluoride anions, which differs markedly among the different frameworks. The simulations showed that the distances from the fluoride anion to the next-nearest neighboring Si atoms are key to determining whether dynamic disorder can occur or not. Although longer-range interactions with the organic structure-directing agents tend to play a less decisive role, they can lead to a suppression of dynamic disorder in some cases. In addition to providing detailed understanding of the behavior of fluoride anions in as-synthesized all-silica zeolites, the findings of the present work could contribute to a further elucidation of their structure-directing role during zeolite synthesis.Wissenschaftlicher ArtikelBand:125Heft:1634 29 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Water Reactions on Reconstructed Rutile TiO2: A Density Functional Theory/Density Functional Tight Binding Approach(American Chemical Society, 2021-06-14); ; ; ; Far from being conclusively understood, the reactive interaction of water with rutile does still present a challenge to atomistic modeling techniques rooted in quantum mechanics. We show that static geometries of stoichiometric TiO2/water interfaces can be described well by density functional tight binding. However, this method needs further improvements to reproduce the low dissociation propensity of H2O after adsorption predicted by density functional theory (DFT). A reliable description of the surface reactivity of water is fundamental to investigate the nonstoichiometric reconstruction of the (001) facet rich in Ti interstitials. Calculations based on DFT predict the transition temperature for the onset of reconstruction in remarkable agreement with experiments and suggest that this surface, in contact with liquid water, can promote spontaneous H2O splitting and formation of H2 molecules.Wissenschaftlicher ArtikelBand:125Heft:2438 45 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Transient Au–CO Complexes Promote the Activity of an Inverse Ceria/Gold Catalyst: An Insight from Ab Initio Molecular DynamicsTo probe particle–support interactions and their mechanistic role for catalytic CO oxidation on nanoporous gold (np-Au) coated with ceria nanoparticles, we carried out ab initio molecular dynamics (AIMD) simulations and standard density functional theory (static DFT) computations. To this end, we studied ceria clusters (Ce10O20/19) supported on a Au(321) surface exhibiting a high density of steps and kinks. Our theoretical model represents the structurally inverse situation compared to more commonly studied ceria-supported Au nanoparticle systems. In agreement with previous results for Au(111), we find that reduced (Ce10O19) as well as stoichiometric (Ce10O20) ceria nanoparticles transfer electrons to the Au(321) support. This charge transfer (particularly strong in the case of Ce10O19) reflecting a strong chemical interaction between ceria and Au is probably responsible for the stabilization of np-Au against thermal coarsening experimentally observed upon deposition of oxide nanoparticles. The adsorption energies of the ceria cluster on Au(321) are more negative than on the Au(111) surface by around ∼0.5 eV. AIMD simulations were employed to study the mechanism of catalytic CO oxidation with O2 for the ceria/Au(321) system. We found that a CO molecule adsorbed near the ceria/gold perimeter interface can extract a Au atom from the surface in the form of a mobile linear Au–CO complex, which results in a very low activation energy when this species reacts with lattice O to CO2. The released bare Au adatom subsequently attaches to a step edge of the gold surface, leading to a dynamic restructuring of the Au support. Next, an activated O2 molecule adsorbed at a perimeter site between ceria and Au reacts with a second CO molecule to CO2 and an adsorbed O atom, which eventually fills the vacancy site created in the first half of the cycle. As compared to ceria particles supported on Au(111), the reactivity is enhanced as a new low-energy mechanism is enabled, revealing the positive impact of the stepped structure of Au(321).Wissenschaftlicher ArtikelBand:125Heft:4847 41 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Influence of Organic Structure-Directing Agents on Fluoride Dynamics in As-Synthesized Silicalite-1Silicalite-1, an all-silica zeolite having the MFI topology, can be synthesized in the presence of fluoride ions, which balance the charge of the cationic organic structure-directing agents (OSDAs; such as tetrapropylammonium). In as-synthesized Silicalite-1, the fluoride anions occupy well-defined positions in the 41·52·62 cages where they are covalently bonded to framework Si atoms. Previous experimental studies showed that the fluoride anions are dynamically disordered at room temperature. The dynamic disorder can be suppressed by cooling to cryogenic temperatures and also through a variation of the OSDA, pointing to an interplay between framework and extra framework dynamics. In the present work, ab initio molecular dynamics (AIMD) simulations in the framework of density functional theory (DFT) were employed to study the influence of the OSDA on the fluoride dynamics, comparing a total of eight alkylammonium OSDAs having either four alkyl chains of equal length (symmetric) or one short and three longer chains (asymmetric). In addition to time-averaged quantities, such as atomic root mean square displacements, the number of dynamic events in which fluoride ions “jump” from one Si atom to a neighboring one was analyzed. While the timescale accessible to the AIMD simulations was found to be too short to observe significant fluoride dynamic disorder at room temperature, it was clearly detectable when increasing the temperature to 373 K. For systems incorporating symmetric OSDAs, increasing the OSDA size correlated with decreasing freedom of motion of the framework atoms. In line with previous experimental findings, a drastic reduction of the fluoride dynamic disorder was observed for systems containing tributylammonium-based OSDAs having one short (methyl or ethyl) chain. Besides reproducing the experimental observations, the computational approach also helped to explain this suppression of the dynamic disorder on the basis of the size and shape of the OSDA.Wissenschaftlicher ArtikelBand:124Heft:1033 30