The most widely used approach to predict catalytic activity is density functional theory, whose results however depend on the adopted exchange‐correlation functional. In this work, the role played by the functional in predicting the activity of single atom catalysts (SAC) in the hydrogen and oxygen evolution reactions (HER and OER) is studied. 16 transition metal (TM) atoms embedded in N‐doped graphene are simulated and the performance of the widely adopted Perdew–Burke–Ernzerhof (PBE) functional against the hybrid PBE0 functional is assessed. The PBE+U approach, a computationally less complex way to correct for the self‐interaction error in density functional theory, is also considered. The predictions obtained with PBE have a substantial deviation from PBE0 for first row TMs, i.e., 3d systems, while smaller deviations are found for the 4d and 5d series. The PBE+U results represent an improvement with respect to PBE, although some differences from PBE0 remain. This study underlines the importance of the choice of the DFT functional in screening new catalysts and in predicting catalytic activities. The use of PBE appears acceptable for 4d and 5d metals, while in the case of 3d systems PBE+U or PBE0 approaches are recommended, in particular for magnetic ground states.

In the present work, an Ir/CeO₂ catalyst was prepared by the deposition–precipitation method and tested in the decomposition of hydrazine hydrate to hydrogen, which is very important in the development of hydrogen storage materials for fuel cells. The catalyst was characterised using different techniques, i.e., X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with X-ray detector (EDX) and inductively coupled plasma—mass spectroscopy (ICP-MS). The effect of reaction conditions on the activity and selectivity of the material was evaluated in this study, modifying parameters such as temperature, the mass of the catalyst, stirring speed and concentration of base in order to find the optimal conditions of reaction, which allow performing the test in a kinetically limited regime.

CO₂ adsorption and activation on Cu single atom catalysts and Cu nanoclusters supported on the (110) surface of rutile and on the (101) surface of anatase TiO₂ have been investigated by means of first principles electronic structure calculations. The role of oxide reduction associated to the presence of oxygen vacancies has been considered. Five main messages emerge from this study. (1) CO₂ activation on Cu/TiO₂ nanostructures is surface sensitive, as the rutile and anatase surfaces can exhibit different behaviors; (2) the surface morphology is essential since CO₂ is activated only when the molecule can simultaneously bind to at least two active sites, such as a Cu atom on one side and an oxide ion on the other site; (3) Cu atoms on TiO₂ are in the +I oxidation state and can bind and activate CO₂ via charge transfer from the oxide; (4) on supported Cu clusters CO₂ activation occurs mostly at the metal/oxide interface; (5) the presence of O vacancy sites facilitates the spontaneous dissociation of CO₂ to CO, or increases the electron density of the metal catalyst, two effects that can influence the mechanism of CO₂ reduction to methanol or other chemicals.

Single Atom Alloys (SAAs) represent one of the most promising class of heterogenous catalysts. They are based on isolated transition metal (TM) atoms stabilized in a host metal matrix. Among others, SAAs are widely studied for processes involving hydrogen, such as water splitting or hydrogenation reactions. On a metal surface the H₂ molecule forms either weakly physisorbed species (H₂ ^phys) or dissociates with formation of chemisorbed H atoms (H*). In electrochemical processes, the adsorption free energy of the H* intermediate is normally used as a descriptor of the catalyst reactivity. Recently, it has been shown that on Single Atom Catalysts (SAC) embedded in carbon-based, sulfide, or oxide supports other species can form, where two H atoms are stably bound to the SAC, forming dihydrogen (H₂*) or dihydride (H*H*) surface species reminiscent of the classical Kubas’s transition metal complexes in coordination chemistry. In this work we show, based on density functional theory calculations, that dihydrogen and dihydride complexes can also form on SAAs and, depending on the nature of the host metal, can be even more stable than two separated chemisorbed H* species (2H*). These new stable intermediates have not been considered so far in the analysis of the mechanism and kinetics of the reaction. The work shows that the possible formation of dihydrogen and dihydride complexes is not limited to SACs but is also valid for SAAs and needs to be considered in the study of hydrogen-based reactions on these systems.