The development of cost-effective and highly efficient catalysts is of scientific importance and practical need in the conversion and utilization of clean energy. One of the strategies fulfilling that demand is to achieve high exposure of a catalytically functional noble metal to reactants to maximize its utilization efficiency. We report herein that the single-atom alloy (SAA) made of atomically dispersed Pt on the surface of Ni particles (Pt is surrounded by Ni atoms) exhibits improved catalytic activity on the hydrolytic dehydrogenation of ammonia−borane, a promising hydrogen storage method for onboard applications. Specifically, an addition of 160 ppm of Pt leads to ca. 3-fold activity improvement in comparison to that of pristine Ni/CNT catalyst. The turnover frequency based on the isolated Pt is 12000 mol H2 mol Pt −1 min −1 , which is about 21 times the value of the best Ptbased catalyst ever reported. Our simulation results indicate that the high activity achieved stems from the synergistic effect between Pt and Ni, where the negatively charged Pt (Pt δ-) and positively charged Ni (Ni δ+ ) in the Pt-Ni alloy are prone to interact with H and OH of H 2 O molecules, respectively, leading to an energetically favorable reaction pathway.

IntroductionA primary goal of molecular modeling is the prediction of structure, stability, and chemical reactivity of molecules that are difficult to investigate by experimental means. Today, there are many methods ranging from simple structure descriptions to molecular mechanics and quantum chemical approaches to fulfill this goal. Each of these models is based on simplifications and assumptions, which should facilitate the task of molecular modeling. Molecular modeling does provide new insights into the properties of molecules and molecular reactivity provided one considers appropriately the assumptions and simplifications made within the model used.Despite the enormous potential and possibilities of molecular modeling with the help of advanced quantum chemiAbstract The bond energy (BE) of a polyatomic molecule cannot be measured and, therefore, determination of BEs can only be done within a model using a set of assumptions. The bond strength is reflected by the intrinsic BE (IBE), which is related to the intrinsic atomization energy (IAE) and which represents the energy of dissociation under the provision that the degree of hybridization is maintained for all atoms of the molecule. IBE and BE differ in the case of CC and CH bonds by the promotion, the hybridization, and the charge reorganization energy of carbon. Since the latter terms differ from molecule to molecule, IBE and BE are not necessarily parallel and the use of BEs from thermochemical models can be misleading. The stretching force constant is a dynamical quantity and, therefore, it is related to the bond dissociation energy (BDE). Calculation and interpretation of stretching force constants for local internal coordinate modes are discussed and it is demonstrated that the best relationship between BDEs and stretching force constants is obtained within the model of adiabatic internal modes. The valence stretching force constants are less suitable since they are related to an artificial bond dissociation process with geometrical relaxation effects suppressed, which leads to an intrinsic BDE (IBDE). In the case of AX n molecules, symmetric coordinates can be used to get an appropriate stretching force constant that is related to the BE. However, in general stretching force constants determined for symmetry coordinates do not reflect the strength of a particular bond since the related dissociation processes are strongly influenced by the stability of the products formed.Keywords Bond energy (BE), Intrinsic bond energy (IBE), Bond dissociation energy (BDE), Force constants, Adiabatic internal mode cal methods, there is still a need to understand the properties and behavior of molecules on the basis of simple models that require no sophisticated calculations. One wants to connect the properties of a molecule with those of atoms, bonds, or small functional groups so that the knowledge of these group properties makes it possible to describe whatever molecule may be constructed from atoms, bonds (diatomic groups) or functional groups. Central to many of the...

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