We demonstrate that the selective hydrogenation of acetylene depends on energy profile of the partial and full hydrogenation routes and the thermodynamic stability of adsorbed C2H2 in comparison to C2H4.

Cubic molybdenum nitride (γ-Mo2N) exhibits Pt-like catalytic behavior in many chemical applications, most notably as a potent catalyst for conversion of harmful NO x gases into N2. Guided by experimental profiles from adsorption of 15NO on γ-Mo2 14N, we map out plausible mechanisms for the formation of the three isotopologues of dinitrogen (14N2, 15N2, and 14N15N) in addition to 14N15NO. By deploying cluster models for the γ-Mo2N­(100) and γ-Mo2N­(111) surfaces, we demonstrate facile dissociative adsorption of NO on γ-Mo2N surfaces. Surfaces of γ-Mo2N clearly activate adsorbed 15NO molecules, as evidenced by high binding energies and the noticeable elongation of the N–O bonds. 15NO molecule dissociates through modest reaction barriers of 24.1 and 28.1 kcal/mol over γ-Mo2N­(100) and γ-Mo2N­(111) clusters; respectively. Dissociative adsorption of a second 15NO molecule produces the experimentally observed Mo2O x N y phase. Over the 100 surface, subsequent uptake of 15NO continues to occur until the dissociated O and N atoms occupy all 4-fold hollow and top sites. We find that, the direct desorption of 15N2 from the Mo2O x N y -like phases phase requires a sizable energy barrier to precede. Considering a preoxygen surface covered cluster reduces this energy barrier only marginally. Desorption of 15N2 molecules takes place upon combination of two adjacent N atoms from top sites via a low-energy multistep Langmuir–Hinshelwood mechanism. Dissociative adsorption of gaseous 15NO molecules at surface Mo–N bonds weakens the Mo–N bonds and leads to formation of 14N15N molecules (where 14N denotes a nitrogen atom originated from surfaces of γ-Mo2N crystals). Liberation of 14N2 molecules occurs via surface diffusion of two surface N atoms on the (111) N-terminated surface. Formation of 14N15NO proceeds via direct abstraction of a surface 14N atom by a gaseous 15NO adduct.

Cerium oxide $\text{CeO}_2$, or ceria, has gained increasing interest owing to its excellent catalytic applications. Under the framework of density functional theory (DFT), this contribution demonstrates the effect that introducing the element nickel (Ni) into the ceria lattice has on its electronic, structural, and optical characteristics. Electronic density of states (DOSs) analysis shows that Ni integration leads to a shrinkage of Ce 4$f$ states and improvement of Ni 3$d$ states in the bottom of the conduction band. Furthermore, the calculated optical absorption spectra of an Ni-doped $\text{CeO}_2$ system shifts towards longer visible light and infrared regions. Results indicate that Ni-doping a $\text{CeO}_2$ system would result in a decrease of the band gap. Finally, Mulliken's charge transfer of the $\text{Ce}_{1-x}\text{Ni}_x\text{O}_2$ system exhibits an ionic bond between Ce or Ni and O, and covalent bonds between Ce and Ni atoms. The analysis of absorption spectra demonstrates that Ni-doped $\text{CeO}_2$ is a material with potential use in photocatalytic, photovoltaic, and solar panels.

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