Search

The process of hydrogen spillover on metal nanoparticle decorated carbon surfaces has been discussed for many years due to its importance for heterogeneous catalysis and hydrogen storage. The present density functional theory (DFT) study supports recent experimental observations of the hydrogen spillover process. By use of model systems of carbon-supported palladium nanoparticles, the details of hydrogen spillover are investigated and the effects of nitrogen doping on such processes are elucidated. It is found that graphitic nitrogen atoms and water molecules significantly facilitate the hydrogen spillover reaction and serve as anchoring sites for the spillover hydrogen atoms.

The noncovalent interaction of the formic acid dimer (FAD) with pyrene and single-walled carbon nanotubes (SWCNTs) is studied using both density functional theory with an empirical dispersion correction as well spin-component-scaled and F12 variants of second-order Møller–Plesset perturbation theory. For the FAD–pyrene model system, it is shown that the dispersion-corrected DFT methods provide similar accurate results for the noncovalent interaction of carboxylic acid dimers with large conjugated π-systems such as MP2 and SCS-MP2. The binding energy of FAD in SWCNTs is found to be sensitive to the radius of the nanotube. It amounts to ca. 22 kcal/mol in the armchair (6,6) SWCNT and decreases with increasing tube radius. In the armchair (8,8) SWCNT, the binding energy is already 25% smaller. To facilitate an experimental identification of FAD inside SWCNTs, we report results for the shifts of the vibrational frequency, where we could identify intense C–O, CO and O–H stretch modes as promising infrared signatures for an experimental detection of such complexes.

The oxidation of 2-propanol by titanium peroxo complexes is investigated in a combined synthetic, spectroscopic, and computational study. We find in quantum chemical calculations for the thermal reaction in protic solvents that the temporary protonation of the peroxo group activates the latter as electrophile. This transient species is amenable to a concerted transfer of two electrons and a proton from the secondary C atom of 2-propanol. Simultaneously, the carbonyl group is formed and the alcoholic proton is transferred to the solvent. In line with the results of the calculations, we find experimentally that the activity of the titanium peroxo complexes as oxidant depends on the pH value of the reaction medium.

The elementary steps of the methanol synthesis reaction at oxygen vacancies on the polar ZnO(0001̅) surface have been studied with density functional theory. We report results for reaction and activation energies for the most important elementary steps of the methanol synthesis reaction on this surface. At these oxygen vacancies the barriers for heterolytic cleavage of H2into protons, bound in surface OH groups, and hydrides, trapped in the vacancies, is low. The stabilized hydride facilitates the reduction of CO to formyl (stabilized in the vacancy) with a low barrier ≲100 kJ/mol. After a fast rearrangement to formaldehyde and hydroxymethylene species, a second reduction step leads probably to a surface-bound methoxide which at reducing conditions desorbs from the surface under regeneration of an oxygen vacancy. Beside formate, which appears as a side product, and formyl species, oxygen-bound hydroxymethylene might be another observable intermediate of the methanol synthesis reaction at oxygen vacancy sites on the ZnO(0001̅) surface.

Cobalt ferrite, CoFe2O4(CFO), nanocrystals are efficient and competitive anode materials in the field of electrochemical water splitting. Using density functional theory with on-site Hubbard Ucorrections (DFT+U), we have investigated the structural, electronic, and magnetic properties of CFO (001)/(100) surfaces, as well as their reactivities toward water adsorption. Special attention has been focused on the formation of oxygen vacancies (VO), due to their key role in the oxidation activity of metal oxides, often based on the Mars–van Krevelen mechanism. Our results show that vacancy formation is easiest at oxygen sites that are not bound to tetrahedrally coordinated Fe. Water adsorbs mainly in molecular form on the Co/Fe metal cations, whereas it dissociates at defects. In comparison to other spinels, CFO is similar to NiFe2O4, exhibiting relatively low energy cost of VOformation and a strong affinity of the vacancies toward water. These findings suggest that CFO may be a more promising oxidation catalyst than NiCo2O4and Co3O4.