The chemical state of ruthenium in the Ru/MgO and Ru−Cs+/MgO catalysts prepared by the incipient wetness technique with the use of Ru(OH)Cl3 and Cs2CO3 as the catalyst and promoter precursors, respectively, is characterized by X-ray photoelectron spectroscopy (XPS). The influence of the final state effects (the differential charging and variations of the relaxation energy) on the binding energy of Ru 3d5/2 core level measured for supported Ru nanoparticles is estimated by comparison of the Fermi levels and the modified Auger parameters determined for the Ru/MgO and Ru−Cs+/MgO catalysts with the corresponding characteristics of polycrystalline Ru foil. High-resolution transmission electron microscopy (HRTEM) in combination with energy dispersive X-ray (EDX) microanalysis reveals that Ru particles in the Ru−Cs+/MgO catalyst are covered with an amorphous layer containing cesium. XPS data show that the layer subjected to the prolonged treatment with H2 at 450 °C consists of cesium suboxide Cs2+ X O. The shift of the Ru 3d5/2 binding energy toward lower values is found for the Ru−Cs+/MgO catalyst (279.7 eV) with respect to metallic Ru (280.2 eV) and the Ru/MgO catalyst (280.5 eV). It is assumed that the shift results from a decrease in the work function of ruthenium under the action of Cs+ cations located on the Ru surface. The data obtained are used to explain the sharp difference in the activities of the Ru/MgO and Ru−Cs+/MgO catalysts for ammonia synthesis at 250−400 °C.

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A nontraditional approach to the development of catalysts for low-temperature ammonia synthesis is considered. The approach is characterized by application of catalysts representing heterogeneous analogs of the known homogeneous nitrogen-fixing systems based on transition metal compounds and strong electron donors. The use of this approach led to the development of catalysts that considerably surpass in their activity (at atmospheric pressure) the industrial catalyst for the ammonia synthesis. Some of the developed catalysts are active in the formation of ammonia from dinitrogen and dihidrogen even at 110--150 ~ The mechanisms of activation and hydrogenation of dinitrogen over these new catalysts are discussed.

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