Chemistry of a catalyst surface during catalysis is crucial for a fundamental understanding of mechanism of a catalytic reaction performed on the catalyst in the gas or liquid phase. Due to the pressure- or molecular density-dependent entropy contribution of gas or liquid phase of the reactants and the potential formation of a catalyst surface during catalysis different from that observed in an ex situ condition, the characterization of the surface of a catalyst under reaction conditions and during catalysis can be significant and even necessary for understanding the catalytic mechanism at a molecular level. Electron-based analytical techniques are challenging for studying catalyst nanoparticles in the gas or liquid phase although they are necessary techniques to employ. Instrumentation and further development of these electron-based techniques have now made in situ/operando studies of catalysts possible. New insights into the chemistry and structure of catalyst nanoparticles have been uncovered over the last decades. Herein, the origin of the differences between ex situ and in situ/operando studies of catalysts, and the technical challenges faced as well as the corresponding instrumentation and innovations utilized for characterizing catalysts under reaction conditions and during catalysis, are discussed. The restructuring of catalyst surfaces driven by the pressure of reactant(s) around a catalyst, restructuring in reactant(s) driven by reaction temperature and restructuring during catalysis are also reviewed herein. The remaining challenges and possible solutions are briefly discussed.

Catalytic complete oxidation of CH4 at relatively low temperatures is significant for removing unburned CH4 from the exhaust of combustion engines fueled with natural gas or liquefied petroleum gas. Here a nanocomposite catalyst (NiO/CeO2) consisting of CeO2 nanorods and supported NiO nanoclusters was prepared by a two-step wet-chemistry method. This nanocomposite catalyst exhibits high catalytic activity for the complete oxidation of CH4 in the temperature range of 350–600 °C. A CH3-like intermediate bound to Ni cations was observed at a relatively low temperature by ambient pressure X-ray photoelectron spectroscopy under catalytic conditions. Parallel kinetic studies of NiO/SiO2, CeO2 and NiO/CeO2 catalysts show that the apparent barrier for complete oxidation of CH4 on NiO/CeO2 (69.4 ± 4 kJ/mol) is much lower than the 95.1 ± 5 kJ/mol of pure CeO2 and 98.4 ± 5 kJ/mol of NiO/SiO2, supported by the turnover frequency of NiO/CeO2 being significantly higher than NiO/SiO2 and CeO2. These differences indicate a synergistic effect between the CeO2 nanorods and the supported NiO nanoclusters. This synergistic effect occurs at the interface of NiO and CeO2, observed in TEM. The lattice oxygen atoms at the interface exhibit high activity based on the lower reduction temperature uncovered in studies of the temperature-programmed reduction of H2.

A pair of room-temperature-stable MnIII–alkylperoxo complexes were characterized and shown to oxidize PPh3. Thermal decomposition studies provide evidence of both homolysis and heterolysis of the MnIII–alkylperoxo O–O bond.

The enzymes manganese lipoxygenase (MnLOX) and manganese superoxide dismutase (MnSOD) utilize mononuclear Mn centers to effect their catalytic reactions. In the oxidized Mn III state, the active site of each enzyme contains a hydroxo ligand, and X-ray crystal structures imply a hydrogen bond between this hydroxo ligand and a cis carboxylate ligand. While hydrogen bonding is a common feature of enzyme active sites, the importance of this particular hydroxo-carboxylate interaction is relatively unexplored. In this present study, we examined a pair of Mn III -hydroxo complexes that differ by a single functional group. One of these complexes, [Mn III (OH)(PaPy 2 N)] + , contains a naphthyridinyl moiety capable of forming an intramolecular hydrogen bond with the hydroxo ligand. The second complex, [Mn III (OH)(PaPy 2 Q)] + , contains a quinolinyl moiety that does not permit any intramolecular hydrogen bonding. Spectroscopic characterization of these complexes supports a common structure, but with perturbations to [Mn III (OH)(PaPy 2 N)] + , consistent with a hydrogen bond. Kinetic studies using a variety of substrates with activated O−H bonds, revealed that [Mn III (OH)(PaPy 2 N)] + is far more reactive than [Mn III (OH)(PaPy 2 Q)] + , with rate enhancements of 15−100-fold. A detailed analysis of the thermodynamic contributions to these reactions using DFT computations reveals that the former complex is significantly more basic. This increased basicity counteracts the more negative reduction potential of this complex, leading to a stronger O−H BDFE in the [Mn II (OH 2 )(PaPy 2 N)] + product. Thus, the differences in reactivity between [Mn III (OH)(PaPy 2 Q)] + and [Mn III (OH)(PaPy 2 N)] + can be understood on the basis of thermodynamic considerations, which are strongly influenced by the ability of the latter complex to form an intramolecular hydrogen bond.