Classification and Identification of Facet- and Edge-Specific γ-AlO Surface Sites from H/Al NMR Cross-Signatures and DFT Modeling.

γ-AlO is used as both a catalyst and a support for catalytic active phases. The properties of γ-AlO have been ascribed to specific surface sites, with varying Al coordination number, acidity, and basicity, depending on the morphology of the material. Here, we combine surface-specific Al{H} 2D high-field NMR (28.

Meeting the Industrial Challenges of CO Photocatalytic Reduction: Moving From Molybdenum Disulfides to Oxysulfides Based Materials?

Reducing CO emissions is one of the greatest challenges of the century. Among the means employed to tackle CO emissions, the photocatalytic conversion of CO is an appealing way to valorize CO since it uses the sun energy, which is abundant. However, nowadays, the best photocatalytic systems still report too low efficiencies, and use expensive materials, so they cannot be readily industrialized for use at large scale.

Tailoring the optoelectronic properties and dielectric profiles of few-layer S-doped MoO and O-doped MoS nanosheets: a first-principles study.

To gain insights into few layer (FL) van der Waals MoOS/MoSO heterostructures for photocatalytic applications, we analyze how the concentration () and location of anionic isovalent atom (S or O) substitutions impact their opto-electronic properties and high frequency dielectric constant profiles. By using density functional theory (DFT) calculations within the HSE06 functional, we show that the electronic band gap of FL MoOS decreases with increasing , while the dielectric constant profile and absorption coefficient in the UV-vis range increase. The stronger band gap reductions are obtained when S-atoms are located in the internal bulk region of FL MoOS and in interaction with O-atoms of the neighboring layer.

PtO Cl (OH) (H O) Complexes under Oxidative and Reductive Conditions: Impact of the Level of Theory on Thermodynamic Stabilities.

Platinum-based catalysts with Cl , OH , O and H O ligands, are involved in many industrial processes. Their final chemical properties are impacted by calcination and reduction applied during the preparation and activation steps. We investigate their stability under these reactive conditions with density functional theory (DFT).

Evaluating acid and metallic site proximity in Pt/γ-AlO-Cl bifunctional catalysts through an atomic scale geometrical model.

Quantifying the distances between metallic sites and acid sites is crucial for tuning the catalytic activity and selectivity of bifunctional catalysts involving sub-nanometric platinum (Pt) nano-particles (NP) highly dispersed on a chlorinated alumina support. Thanks to the quantitative use of high resolution scanning transmission electron microscopy in the high angle annular dark field mode, we first highlight the presence of few Pt NP together with Pt single atoms (SA) on γ-alumina supports exhibiting various morphologies (flat-like or egg-like), and chlorine (Cl) and Pt loadings. We demonstrate that increasing the Pt loading does not impact the NP sizes but only the Pt NP inter-distances, whereas the Cl loading influences the SA/NP proportion.

Electronic structures of the MoS/TiO (anatase) heterojunction: influence of physical and chemical modifications at the 2D- or 1D-interfaces.

To tackle the challenge of CO photoreduction, semiconducting layered transition metal dichalcogenides like MoS have attracted much attention due to their tunable 2D nano-structures. By using advanced periodic density functional theory calculations (HSE06 functional), we provide a systematic quantification of the optoelectronic properties of various interfacial heterostructures composed of 2H-MoS and anatase TiO. We systematically determine the band gaps, and conduction band (CB) and valence band (VB) positions to figure out the nature of the heterojunction.

2D MoOS/MoS van der Waals Assembly: A Tunable Heterojunction with Attractive Properties for Photocatalysis.

Two-dimensional (2D) van der Waals (vdW) heterostructures currently have attracted much attention in widespread research fields where semiconductor materials are key. With the aim of gaining insights into photocatalytic materials, we use density functional theory (DFT) calculations within the HSE06 functional to analyze the evolution of optoelectronic properties and high-frequency dielectric constant profiles of various 2D MoOS/MoS heterostructures modified by chemical and physical approaches. Although the MoO/MoS heterostructure is a type III heterojunction associated with a metallic character, we found that exchanging the terminal oxo atoms of the MoOS single layer (SL) with sulfur enables shifting its CB position above the VB position of the MoS SL.

Dynamic Features of Transition States for β-Scission Reactions of Alkenes over Acid Zeolites Revealed by AIMD Simulations.

Zeolite-catalyzed alkene cracking is key to optimize the size of hydrocarbons. The nature and stability of intermediates and transition states (TS) are, however, still debated. We combine transition path sampling and blue moon ensemble density functional theory simulations to unravel the behavior of C alkenes in CHA zeolite.

Atomic Description of the Interface between Silica and Alumina in Aluminosilicates through Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy and First-Principles Calculations.

Despite the widespread use of amorphous aluminosilicates (ASA) in various industrial catalysts, the nature of the interface between silica and alumina and the atomic structure of the catalytically active sites are still subject to debate. Here, by the use of dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) and density functional theory (DFT) calculations, we show that on silica and alumina surfaces, molecular aluminum and silicon precursors are, respectively, preferentially grafted on sites that enable the formation of Al(IV) and Si(IV) interfacial sites. We also link the genesis of Brønsted acidity to the surface coverage of aluminum and silicon on silica and alumina, respectively.

Tuning the metal-support interaction by structural recognition of cobalt-based catalyst precursors.

Controlling the nature and size of cobalt(II) polynuclear precursors on γ-alumina and silica-alumina supports represents a challenge for the synthesis of optimal cobalt-based heterogeneous catalysts. By density functional theory (DFT) calculations, we show how after drying the interaction of cobalt(II) precursor on γ-alumina is driven by a structural recognition phenomenon, leading to the formation of an epitaxial Co(OH)2 precipitate involving a Co-Al hydrotalcite-like interface. On a silica-alumina surface, this phenomenon is prevented due to the passivation effect of silica domains.

Tuning the properties of visible-light-responsive tantalum (oxy)nitride photocatalysts by non-stoichiometric compositions: a first-principles viewpoint.

Finding an ideal photocatalyst for achieving efficient overall water splitting still remains a great challenge. By applying accurate first-principles quantum calculations based on DFT with the screened non-local hybrid HSE06 functional, we bring rational insights at the atomic level into the influence of non-stoichiometric compositions on essential properties of tantalum (oxy)nitride compounds as visible-light-responsive photocatalysts for water splitting. Indeed, recent experiments show that such non-stoichiometry is inherent to the nitridation methods of tantalum oxide with unavoidable oxygen impurities.

Monitoring morphology and hydrogen coverage of nanometric Pt/γ-Al2 O3 particles by in situ HERFD-XANES and quantum simulations.

Platinum nanoclusters highly dispersed on γ-alumina are widely used as heterogeneous catalysts. To understand the chemical interplay between the Pt nanoparticles, the support, and the reductive atmosphere, we performed X-ray absorption near edge structure (XANES) in situ experiments recorded in high energy resolution fluorescence detection (HERFD) mode. Spectra are assigned by comparison with simulated XANES spectra on models obtained by molecular dynamics (DFT-MD).

Hydrogenation properties of KSi and NaSi Zintl phases.

The recently reported KSi-KSiH(3) system can store 4.3 wt% of hydrogen reversibly with slow kinetics of several hours for complete absorption at 373 K and complete desorption at 473 K. From the kinetics measured at different temperatures, the Arrhenius plots give activation energies (E(a)) of 56.

CO adsorption on amorphous silica-alumina: electrostatic or Brønsted acidity probe?

The adsorption of CO on amorphous silica-alumina (ASA) was calculated by DFT. CO appears as a probe of the electrostatic field induced by the whole surface, at the origin of a so-called vibrational Stark effect responsible for the CO frequency shifts. Brønsted acidity of the ASA sites does not directly correlate CO frequency shifts.

Potassium silanide (KSiH3): a reversible hydrogen storage material.

KSi silicide can absorb hydrogen to directly form the ternary KSiH(3) hydride. The full structure of α-KSiD(3), which has been solved by using neutron powder diffraction (NPD), shows an unusually short Si-D lengths of 1.47 Å.

Growth of boehmite particles in the presence of xylitol: morphology oriented by the nest effect of hydrogen bonding.

The ability to design nanoparticles size and shape through the addition of simple and commercially available organic molecules is of particular interest in the catalytic domain because huge amounts of very fine powders are needed. The origin of this effect is all the more difficult to elucidate because the involved interactions are weak. In this paper, we have investigated the shaping of boehmite AlO(OH) nanoparticles in the presence of polyols like xylitol (C(5) alditol) by a combined experimental and theoretical approach.

Topological Analysis of the Interactions between Organic Molecules and Co(Ni)MoS Catalytic Active Phases.

The adsorption modes of toluene, 2,3-dimethylbut-1-ene, and 2-methylthiophene on the edges of Co(Ni)MoS nanocrystallites has been investigated with the ELF topological approach of chemical bonding. The chemisorbed modes are characterized by the formation of bonding basins linking the substrate to the catalytic sites. The electronic rearrangements within the substrate are discussed.

Pseudo-bridging silanols as versatile Brønsted acid sites of amorphous aluminosilicate surfaces.

Amorphization tunes acidity: Pseudo-bridging silanols, suggested as versatile Brønsted acid groups by molecular modeling studies, are obtained by shifted hydrolysis of Si-O-Al bridges formed by the thermal treatment of silica deposited on gamma-Al(2)O(3) (100), and appear under given pretreatment conditions. Demixing of part of the silica from the aluminosilicate phase is predicted upon excess water adsorption.

Atomic scale insights on chlorinated gamma-alumina surfaces.

The thermochemistry of chlorinated gamma-alumina surfaces is explored by means of density functional calculations as a function of relevant reaction conditions used in experiments and in high-octane fuel production in the refining industry such as hydrocarbon isomerization and reforming. The role of chlorine as a dope of the Brønsted acidity of gamma-alumina surfaces is investigated at an atomic scale. Combining infrared spectroscopy and density functional theory calculations, the most favorable location of chlorine atoms on the (110), (100) and (111) surfaces of gamma-alumina is found to result either from direct adsorption or from the exchange of basic hydroxyl groups.

Quantum chemical and vibrational investigation of sodium exchanged gamma-alumina surfaces.

The sodium cation is well known as an efficient poison of gamma-alumina surface acidity. This poisoning effect has been revealed both by characterization methods and catalytic tests. In this work, we propose an accurate model of sodium exchanged gamma-alumina surfaces.

Influence of the hydroxylation of gamma-Al2O3 surfaces on the stability and diffusion of single Pd atoms: a DFT study.

Using recent well-defined models of gamma-Al2O3 surfaces, we study the interaction of single Pd atoms with gamma-Al2O3 surfaces corresponding to realistic pretreatment conditions by means of density functional theory periodic calculations. For relevant hydroxylation states of the surface, we determine potential energy surfaces (PES) that depict the relationship between structure and interaction at the metal-oxide interface. This approach enables the determination of the low-energy diffusion paths of the adsorbed Pd species.