The metal-cluster formation model for the vapor deposition of Pd atoms on MgO(100) surface has been theoretically established from B3LYP Density Functional Theory calculations by using an embedded cluster model. The results suggest that Pd atoms first nucleate at the oxygen vacancy. As the cluster grows in size, the difference in the binding energy of the cluster to the vacancy and on the flat surface decreases making it easier for the cluster to move out of the vacancy. The exposed vacancy becomes a new nucleation center again. This cluster formation model can explain the experimental observation of a uniform size distribution and island growth.

A molecular modeling study using density functional theory was carried out in order to get an insight of the thermodynamics and mechanisms for NH3 evolution during the reaction of hydrogen with nitrogen containing carbonaceous materials using pyridinic nitrogen species as a model. Both zigzag and armchair configurations were used to model the local structure of the carbonaceous materials. Based on thermodynamic argument, we propose reaction mechanisms that involve consecutive hydrogenation steps and rearrangements that lead to the formation of C–NH2 groups. Dissociation of the C–N bond releases NH2 radicals to the gas phase. NH3 can be produced either through homogeneous or heterogeneous hydrogen abstraction or recombination reactions. It was found that the first hydrogenation reaction is highly exothermic, further hydrogenations are endothermic. Several pathways for NH3 evolution were proposed, most of them are exothermic reactions. Rate constants for the NH2 desorption step were calculated using the transition state theory.

The electronic structures of Ni, Pd, Pt, Cu, and Zn atoms adsorbed on the perfect MgO(1 0 0) surface and on a surface oxygen vacancy have been studied at the DFT/B3LYP level of theory using both the bare cluster and embedded cluster models. Ni, Pd, Pt, and Cu atoms can form stable adsorption complexes on the regular O site of the perfect MgO(1 0 0) surface with the binding energies of 19.0, 25.2, 46.7, and 17.3 kcal/mol, respectively, despite very little electron transfer between the surface and the metal atoms. On the other hand, adsorptions of Ni, Pd, Pt, and Cu atoms show strong interaction with an oxygen vacancy on the MgO(1 0 0) surface by transferring a significant number of electron charges from the vacancy to the adsorbed metal atoms and thus forming ionic bonds with the vacancy site. These interactions on the vacancy site for Ni, Pd, Pt, and Cu atoms increase the binding energies by 25.8, 59.7, 85.2, and 19.1 kcal/mol, respectively, compared to those on the perfect surface. Zn atom interacts very weakly with the perfect surface as well as the surface oxygen vacancy. We observed that the interaction increases from Ni to Pt in the same group and decreases from Ni to Zn in the same transition metal period in both perfect and vacancy systems. These relationships correlate well with the degrees of electron transfer from the surface to the adsorbed metal atom. The changes in the ionization potentials of the surface also correlate with the adsorption energies or degrees of electron transfers. Madelung potential is found to have significant effects on the electronic properties of metal atom adsorptions on the MgO(1 0 0) surface as well as on an oxygen vacancy, though it is more so for the latter. Furthermore, the Madelung potential facilitates electron transfer from the surface to the adsorbed metal atoms but not in the other direction.

A systematic density functional theory (DFT) study of the hydrogen reactions with carbonaceous surfaces was carried out in order to provide molecular-level understanding on the mechanisms of chemical processes involved in carbon hydrogasification. It was found that hydrogen is dissociatively chemisorbed on the active sites of zigzag and armchair configurations of carbonaceous models. In addition, mechanisms for methane and ethane production during the carbon–H2 reaction were proposed suggesting that methane formation is exothermic and ethane formation is also possible but with a much lesser extent. These results agree with available experimental observations. Rate constants of the rate limiting steps were also calculated using the transition state theory. From both the thermodynamic and kinetic points of view, methane formation is much easier from zigzag edges rather than from armchair edges. The large activation energies for both pathways suggest that these reactions are favored at high temperatures.

We present an experimental and theoretical study to provide further insight into the mechanism of CO2 chemisorption on carbonaceous surfaces. The differential heat of CO2 adsorption at low and high coverages was determined in the temperature range 553–593 K. We found that the heat profile has two distinct energetic zones that suggest two different adsorption processes. In the low-coverage region, the heat of adsorption decreases rapidly from 75 to 24 kcal/mol, suggesting a broad spectrum of binding sites. In the high-coverage region, the heat becomes nearly independent of the loading, from 9 to 5 kcal/mol. A systematic molecular modeling study of CO2 chemisorption on carbonaceous surfaces was performed. Several of the carbon–oxygen complexes that have been proposed in the literature were identified and characterized. The calculated adsorption energies are within the experimental uncertainty of the heat of adsorption at low coverage. Pre-adsorbed oxygen groups decrease the exothermicity of CO2 adsorption. In the high-coverage region, our theoretical results suggest that CO2 molecules are likely to adsorb on surface oxygen complexes and on graphene planes.