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Ammonia (NH.sub.3) is pivotal to the fertilizer industry and one of the most commonly produced chemicals.sup.1. The direct use of atmospheric nitrogen (N.sub.2) had been challenging, owing to its large bond energy (945 kilojoules per mole).sup.2,3, until the development of the Haber-Bosch process. Subsequently, many strategies have been explored to reduce the activation barrier of the N[identical to]N bond and make the process more efficient. These include using alkali and alkaline earth metal oxides as promoters to boost the performance of traditional iron- and ruthenium-based catalysts.sup.4-6 via electron transfer from the promoters to the antibonding bonds of N.sub.2 through transition metals.sup.7,8. An electride support further lowers the activation barrier because its low work function and high electron density enhance electron transfer to transition metals.sup.9,10. This strategy has facilitated ammonia synthesis from N.sub.2 dissociation.sup.11 and enabled catalytic operation under mild conditions; however, it requires the use of ruthenium, which is expensive. Alternatively, it has been shown that nitrides containing surface nitrogen vacancies can activate N.sub.2 (refs. .sup.12-15). Here we report that nickel-loaded lanthanum nitride (LaN) enables stable and highly efficient ammonia synthesis, owing to a dual-site mechanism that avoids commonly encountered scaling relations. Kinetic and isotope-labelling experiments, as well as density functional theory calculations, confirm that nitrogen vacancies are generated on LaN with low formation energy, and efficiently bind and activate N.sub.2. In addition, the nickel metal loaded onto the nitride dissociates H.sub.2. The use of distinct sites for activating the two reactants, and the synergy between them, results in the nickel-loaded LaN catalyst exhibiting an activity that far exceeds that of more conventional cobalt- and nickel-based catalysts, and that is comparable to that of ruthenium-based catalysts. Our results illustrate the potential of using vacancy sites in reaction cycles, and introduce a design concept for catalysts for ammonia synthesis, using naturally abundant elements. Ammonia is synthesized using a dual-site approach, whereby nitrogen vacancies on LaN activate N.sub.2, which then reacts with hydrogen atoms produced over the Ni metal to give ammonia., Author(s): Tian-Nan Ye [sup.1] , Sang-Won Park [sup.1] , Yangfan Lu [sup.1] , Jiang Li [sup.1] , Masato Sasase [sup.1] , Masaaki Kitano [sup.1] [sup.2] , Tomofumi Tada [sup.1] , [...]

FeSb2 is known as a potential low-temperature thermoelectric material with the record-high power factor (PF) originating from the huge phonon drag thermopower (Sg). However, the Sg contribution to PF has been observed only at very low temperatures (T) < 40 K. In this paper, we found that the Sg persists at much higher T up to 240 K and enhances PF in FeSb2 thin films deposited on SrTiO3 single crystals. The FeSb2 films showed phonon drag Sg peak at T ∼ 60 K, and the Sg peak value was largely enhanced from 56 to 208 μV/K by varying film thicknesses from 10 to 100 nm. Due to thickness-dependent Sg contribution, the maximum PF = 31.3 μW/(cm K2) was obtained for a 37-nm thick film. In addition, the onset temperature, where Sg starts to appear, can be largely increased due presumably to the enhanced electron–phonon interaction by phonon leakage from the SrTiO3 substrate to the thin FeSb2 layer. Heterostructuring with an oxide would be an effective approach to enhance the phonon drag effect to increase PF in higher T regions for future thermoelectric cooling and energy conversion devices. [ABSTRACT FROM AUTHOR]

Nickel is a promising candidate as an alternative to ruthenium for an ammonia decomposition catalyst. However, the performance of Ni‐based catalysts for ammonia decomposition is still not sufficient to achieve a good hydrogen production rate under low‐temperature because the weak nitrogen affinity of Ni reduces the frequency of the ammonia decomposition reaction. Here, it is reported that Ni supported on barium titanium oxynitride (Ni/h‐BaTiO3−xNy) with a hexagonal structure acts as a highly active and water‐durable catalyst for ammonia decomposition. The operation temperature is reduced by over 140 °C when N3− ions are substituted onto the O2− sites of the BaTiO3 lattice, and the Ni/h‐BaTiO3−xNy catalyst significantly outperforms conventional oxide‐supported Ni catalysts for ammonia decomposition. Furthermore, the activity of Ni/h‐BaTiO3−xNy remains unchanged after exposure to water. The 15NH3 decomposition reaction and Fourier transform‐infrared spectroscopy (FT‐IR) measurements reveal that lattice nitrogen vacancy sites on h‐BaTiO3−xNy function as the active sites for ammonia decomposition. The ammonia decomposition activity of Ni/h‐BaTiO3−xNy is also higher than that of the Ni/h‐BaTiO3−xHy oxyhydride catalyst, making a contrast to the activity trend in ammonia synthesis. [ABSTRACT FROM AUTHOR]

The electronic structures of active sites fundamentally determine the catalytic performance in chemical reactions and are also crucial for obtaining a detailed understanding of charge transport and reaction mechanisms. In this study, the regulation of the electronic structure of active metal Pd can be achieved through a multi-step electron transfer process formed by a synergy of [Ca24Al28O64]4+(e−)4 (C12A7:e−) electride and conductive graphene (Gr). The composite catalytic system (Pd/Gr/C12A7:e−) significantly facilitates the transfer of electrons from electron-rich Pd active sites to aryl halides in Suzuki-coupling reactions, which enables superior catalytic performance with TOFs above 20 times higher than well-studied negatively charged Pd catalysts. No catalytic degradation was observed even after impregnating the catalyst in water because of the well-protected C12A7:e− electride by Gr. The present efficient catalyst can further trigger various carbon–carbon cross-coupling reactions with high activities. These results provide significant advantages for expanding the potential applications of electride materials, thereby allowing precise control of the electronic structure of the active sites and aiding in tuning the reaction conditions using a simple method. [ABSTRACT FROM AUTHOR]