TiO2-Supported Re as a General and Chemoselective Heterogeneous Catalyst for Hydrogenation of Carboxylic Acids to Alcohols

TiO2-supported Re, Re/TiO2, was found to promote selective hydrogenation of carboxylic acids having aromatic and aliphatic moieties to the corresponding alcohols. Re/TiO2 showed superior results compared to other transition-metal-loaded TiO2 and supported Re catalysts for selective hydrogenation of 3-phenylpropionic acid. 3phenylpropanol was produced in 97% yield under mild conditions (5 MPa H-2 at 140 degrees C). Contrary to typical heterogeneous catalysts, Re/TiO2 does not lead to the formation of dearomatized byproducts. The catalyst is recyclable and shows a wide substrate scope in the synthesis of alcohols (22 examples; up to 97% isolated yield)

Factors determining surface oxygen vacancy formation energy in ternary spinel structure oxides with zinc

Spinel oxides are an important class of materials for heterogeneous catalysis including photocatalysis and electrocatalysis. The surface O vacancy formation energy (E-Ovac) is a critical quantity for catalyst performance because the surface of metal oxide catalysts often acts as a reaction site, for example, in the Mars-van Krevelen mechanism. However, experimental evaluation of E-Ovac is very challenging. We obtained the E-Ovac for (100), (110), and (111) surfaces of normal zinc-based spinel oxides ZnAl2O4, ZnGa2O4, ZnIn2O4, ZnV2O4, ZnCr2O4, ZnMn2O4, ZnFe2O4, and ZnCo2O4. The most stable surface is (100) for all compounds. The smallest E-Ovac for a surface is the largest in the (100) surface except for ZnCo2O4. For (100) and (110) surfaces, there is a good correlation, over all spinels, between the smallest E-Ovac for the surface and bulk formation energy, while the ionization potential correlates well in (111) surfaces. Machine learning over E-Ovac of all surface sites in all orientations and for all compounds to find the important factors, or descriptors, that decide the E-Ovac revealed that bulk and surface-dependent descriptors are the most important, namely the bulk formation energy, a Boolean descriptor of whether the surface is (111) or not, and the ionization potential, followed by geometrical descriptors that are different in each O site

Surface Oxygen Vacancy Formation Energy Calculations in 34 Orientations of beta-Ga2O3 and theta-Al2O3

Computational exploration of previously unknown reactive sites is a powerful strategy for the emergence of new catalytic reactions. Exotic surfaces can be theoretically investigated, but there are very few, if any, computational models of high-index orientations that consider the reconstruction of the surface. A workflow to efficiently obtain a set of accessible terminations by removing those that are metastable against macroscopic facet formation and by comparing cleaved surfaces and surfaces suggested by a genetic algorithm (GA) for promising orientations is proposed and demonstrated using 34 orientations of beta-Ga2O3 and theta-Al2O3. Seven and six terminations considered to be experimentally accessible are found for beta-Ga2O3 and theta-Al2O3, respectively, where the highest surface energy was roughly twice that of the lowest. The lowest surface 0 vacancy formation - energies (E-Ovac) among accessible surfaces are 3.04 and 5.46 eV in the (101) and (20 (1) over bar) terminations for beta-Ga2O3 and theta-Al2O3, respectively, where the decreases in E-Ovac, from the most stable surface are 1.32 and 1.11 eV, respectively. The E-Ovac in accessible surfaces showed a good correlation with the descriptors of the local coordination environment, suggesting that exploiting surface O in an unfavorable environment in an accessible termination would enhance O-vacancy-related catalyst performance even in materials that do not show reactivity on the most stable surface

Low-Mode Conformational Search Method with Semiempirical Quantum Mechanical Calculations: Application to Enantioselective Organocatalysis

A conformational search program for finding low-energy conformations of large noncovalent complexes has been developed. A quantitatively reliable semiempirical quantum mechanical PM6-DH+ method, which is able to accurately describe noncovalent interactions at a low computational cost, was employed in contrast to conventional conformational search programs in which molecular mechanical methods are usually adopted. Our approach is based on the low-mode method whereby an initial structure is perturbed along one of its low-mode eigenvectors to generate new conformations. This method was applied to determine the most stable conformation of transition state for enantioselective alkylation by the Maruoka and cinchona alkaloid catalysts and Hantzsch ester hydrogenation of imines by chiral phosphoric acid. Besides successfully reproducing the previously reported most stable DFT conformations, the conformational search with the semiempirical quantum mechanical calculations newly discovered a more stable conformation at a low computational cost

Linear Correlations between Adsorption Energies and HOMO Levels for the Adsorption of Small Molecules on TiO2 Surfaces

Adsorption is a fundamental step in catalysis on a solid surface, and therefore, its understanding is important for explaining its behavior. This work investigated the adsorption of various small molecules, including H-2, N-2, CO, CO2, CH4, NH3, H2O, H2S, dimethyl sulfoxide, alkanes, alkenes, alkynes, aromatic compounds, alcohols, aldehydes, ketones, nitriles, carboxylic acids, amides, and amines, on the anatase (101) and rutile (110) surfaces of TiO2, using periodic density functional theory calculations and statistical methods. Adsorption energies were computed at the same level of theory to obtain a clean and consistent data set. A linear relationship was observed between the adsorption energies of these molecules and their highest occupied molecular orbital (HOMO) levels, whereas no obvious correlation was evident for the lowest unoccupied molecular orbital levels. Improved correlations between the adsorption energies and HOMO levels were generated by dividing these, molecules into two subgroups: hydrocarbons and heteroatom- containing compounds. Interactions between frontier molecular orbitals and the surfaces were considered, to gain a better understanding of the significant correlations that were identified. The data show that these relationships can be primarily ascribed to the interactions between the HOMO of the small molecule and conduction state of the TiO2 surface. The statistical analysis using machine learning demonstrated that the HOMO and dipole moment are the first and second most important properties, respectively, in terms of rationalizing and predicting the adsorption energies

Enantioselective Alkylation by Binaphthyl Chiral Phase-Transfer Catalysts: A DFT-Based Conformational Analysis

A conformational search method based on the density functional theory (DFT) was successfully applied to explore a mechanism for the highly enantioselective alkylation by binaphthyl-modifed chiral phase-transfer catalysts. Key interactions that govern the enantioselectivity were analyzed. The computational results are encouraging for further application of the DFT-based conformational search toward the rational design of next-generation asymmetric phase transfer catalysts

Frontier Molecular Orbital Based Analysis of Solid-Adsorbate Interactions over Group 13 Metal Oxide Surfaces

Adsorption is an essential process that takes place in heterogeneous catalysis. In the current study, solid-adsorbate interactions occurring between a variety of small molecules and surfaces of group beta metal oxides, including beta-Ga2O3(100), beta-Ga2O3(001), theta-Al2O3 (100), theta-Al2O3 (001), theta-Al2O3 (010), In2O3(110), and In2O3(111), were investigated using density functional theory calculations and a machine learning (ML)-based statistical method. The adsorbates utilized for this purpose include CO, CO2, ND NH3, H2O, acetonitrile, acetone, acetamide, acetic acid, alkanes, alkenes, aromatic compounds, alcohols, and amines. The results show that the adsorption energies (E-ads) of each metal oxide surface correlate linearly with the highest occupied molecular orbital (HOMO) energies of the adsorbates and not with energies of the lowest unoccupied molecular orbital (LUMO) of the small molecules. Moreover, in these systems, contributions to molecular adsorption are dominated by interactions between the HOMOs of the adsorbates and the surface conduction band of the metal oxides. Furthermore, the surface energy was found to be an important parameter influencing E-ads values of different metal oxides. Finally, the results of statistical analysis using a ML approach confirmed that adsorbate HOMOs and surface energy of metal oxides are the most influential factors governing molecular adsorption, and also demonstrated that dipole moments of adsorbates contribute to controlling to adsorption