Origins of solvent-induced enhancement in catalytic reactivity and product selectivity are discussed with computational methods to study them.

Of the three mechanisms for activation of methane on copper and copper oxide surfaces, the under-coordinated Cu–O site pair mediated mechanism on CuO surfaces has the lowest activation energy barriers.

The mechanism of glucose ring opening and isomerization to fructose, catalyzed by the Lewis acid catalyst CrCl3 in the presence of water, is investigated using Car-Parrinello molecular dynamics with metadynamics. Minimum energy pathways for the reactions are revealed and the corresponding free energy barriers are computed. Addition of glucose replaces two water molecules in the active [Cr(H2O)5OH](+2) complex, with two hydroxyl groups of glucose taking their place. Ring opening and isomerization reactions can only proceed if the first step involving the deprotonation of glucose is accompanied by the protonation of the OH(-) group in the partially hydrolyzed metal center ([Cr(C6H12O6)(H2O)3OH](+2) → [Cr(C6H11O6)(H2O)4](+2)). This provides further evidence that the partially hydrolyzed [Cr(H2O)5OH](+2) is the active species catalyzing ring opening and isomerization reactions and that unhydrolyzed Cr(+3) may not be able to catalyze the reactions. After the ring opening, the isomerization reaction proceeds via deprotonation, followed by hydride shift and the back donation of the proton from the metal complex to the sugar. Water molecules outside the first coordination sphere of the metal complex participate in the reaction for mediating the proton transfer. The hydride shift in the isomerization is the overall rate limiting step with a free energy barrier of 104 kJ mol(-1). The simulation computed barrier is in agreement with experiments.

Transition metal oxides are an important class of catalytic materials widely used in the chemical manufacturing and processing industry, owing to their low cost, high surface area, low toxicity, and easily tunable surface and structural properties. For these strongly correlated transition metal oxides, standard approximations in the density functional theory (DFT) exchange-correlation functional fail to describe the electron localization accurately due to the intrinsic errors arising from electron self-interactions. DFT+U method is a widely used extension of DFT, where the Hubbard U term is an onsite potential which puts a penalty on electron delocalization, successfully describing such systems at only slightly higher computational cost than standard DFT methods. The U-value is usually chosen based on its accuracy in reproducing bulk properties like lattice parameters and band structure. However, chemical reactions on transition metal oxide surfaces involve complex surface−adsorbate interactions, and using the bulk properties based U-values in a locally changing surface environment may not describe reaction energetics correctly. Hence, in the current DFT+U benchmarking work, using CuO as a model transition metal oxide, we perform DFT+U calculations to investigate the dissociative chemisorption of H 2 on it. It is observed that the U-value impacts computed adsorption enthalpies by over 100 kJ mol −1 . The DFT+U calculated adsorption enthalpy is compared with the experimental adsorption enthalpy, and equilibrium adsorption configurations are confirmed using infrared analysis. We reveal that the commonly used U-value of 7 eV (fitted against CuO bulk properties) overestimates the adsorption enthalpy by 20−40 kJ mol −1 . The U-value between 4.5 and 5.5 eV correctly predicts the adsorption of H 2 on CuO. The DFT+U benchmarking procedure elucidated in this article, encapsulates surface−adsorbate interactions, surface reactivity, and the dynamic surface reaction environment and, thus, provides an appropriate U-value to be used to model reactions on metal oxide surfaces.

Glycerol was oxidized selectively to oxalic and tartronic acids in 78% yield over a highly crystalline CuO catalyst prepared within a few minutes by a sonochemical synthesis.