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AbstractWe report a nickel complex for catalytic oxidation of ammonia to dinitrogen under ambient conditions. Using the aryloxyl radical 2,4,6‐tri‐tert‐butylphenoxyl (tBu3ArO⋅) as a H atom acceptor to cleave the N−H bond of a coordinated NH3 ligand up to 56 equiv of N2 per Ni center can be generated. Employing the N‐oxyl radical 2,2,6,6‐(tetramethylpiperidin‐1‐yl)oxyl (TEMPO⋅) as the H‐atom acceptor, up to 15 equiv of N2 per Ni center are formed. A bridging Ni‐hydrazine product identified by isotopic nitrogen (15N) studies and supported by computational models indicates the N−N bond forming step occurs by bimetallic homocoupling of two paramagnetic [Ni]−NH2 fragments. Ni‐mediated hydrazine disproportionation to N2 and NH3 completes the catalytic cycle.

Abstract The configuration of a latent heat thermal energy storage (LHTES) is an important factor considered by manufacturers of heat storage systems. In this study, an applicable and low-cost way of improving melting behavior in a rectangular cavity was remarked. There was a preconceived idea that with a single conductive baffle, embedded on the upper wall of the cavity, the melting rate and the amount of heat storage could improve. Therefore, for different locations as well as lengths of a baffle, the heat transfer and melting characteristic of gallium as a phase change material (PCM) in a rectangular cavity were investigated numerically. The cavity has the insulated upper and bottom walls. The sidewalls are regarded to have constant temperatures one higher and another lower than the melting point of gallium. The phase change process is modeled with the fixed grid-based enthalpy-porosity method coupled with the semi-implicit method for pressure-linked equations (SIMPLE) algorithm. The isotherm lines and streamlines, as well as the liquid fraction and Nusselt number on the hot wall, are considered to present the results at a constant Rayleigh number equal to 106. The results show the baffle imposes noticeable improvement on the melting process of gallium in a rectangular cavity by influencing the feature of convective heat transfer. Investigating the different baffle’s locations (LX/L = 0.2 to 0.9) revealed that when the baffle located at the right half of the cavity, melting initiates from the left side, the more amount of PCM melts in comparison with the other cases. Ultimately, the dimensionless location of LX/L = 0.8 demonstrates the best melting characteristic and the most final liquid fraction. The more liquid-fraction, the more energy storing concluded. It also observed a dimensionless height of LY/L = 0.4 represents the most liquid-fraction compared to the heights of LY/L = 0.2, 0.3, and 0.4.