Synthesis of Molybdenum Nitrides
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hesis of Molybdenum Nitrides V. M. Orlova, *, R. N. Osaulenkob, and V. Ya. Kuznetsova aTananaev Institute of Chemistry and Technology of Rare Elements and Minerals (separate subdivision), Kola Scientific Center
(Federal Research Center), Russian Academy of Sciences, Apatity, Murmansk oblast, 184209 Russia b Petrozavodsk State University, Petrozavodsk, 185910 Karelia, Russia *e-mail: [email protected] Received December 30, 2019; revised July 2, 2020; accepted July 2, 2020
Abstract—We have studied the effect of precursors on the synthesis conditions and characteristics of molybdenum nitrides. Mo, MoO3, and MgMoO4 powders were nitrided in flowing ammonia at temperatures in the range 500–800°C. The use of molybdenum nanopowder as a precursor has made it possible to reduce the synthesis temperature and time. We have demonstrated the possibility of direct ammonolysis of the double oxide MgMoO4. Using this molybdate, we have obtained a material with a specific surface area up to 29 m2/g, which is a factor of 2 to 3 larger than that reached by nitriding MoO3. In all cases, the synthesis products consisted of the γ- and β-phases of Mo2N, with cubic and tetragonal lattices, respectively. Keywords: nitridation, molybdenum, molybdenum trioxide, magnesium molybdate, molybdenum nitride, ammonia DOI: 10.1134/S0020168520110102
INTRODUCTION Technological progress is impossible without using novel functional materials, for example, such as transition metal nitrides [1]. One of them is molybdenum nitride, Mo2N. It exists in two polymorphs: tetragonal (β) and face-centered cubic (γ) [2]. Mo2N is thought to be a promising catalyst for a variety of processes, including ammonia synthesis, hydrodesulfurization (HDS) of fuel, and oil hydrodenitrogenation (HDN) [3–5]. There are several ways of preparing molybdenum nitride powders. Verkhoglyadova et al. [6] examined the feasibility of preparing nitrides via nitrogenation of metallic molybdenum powder with an average particle size in the range 2–7 μm. An attempt to prepare nitrides in a nitrogen atmosphere at temperatures from 400 to 1000°C was unsuccessful. Nitrogenation in flowing ammonia for 4 h at a temperature of 700°C yielded the Mo2N nitride containing 6.8% nitrogen. There are several processes for Mo2N synthesis with the use of molybdenum pentachloride as a precursor [7–9]. O’Loughlin et al. [7] prepared γ-Mo2N by reacting MoCl5 with Ca3N2 at a pressure of 57 kbar. The addition of 3 mol NH4Cl to the starting mixture allowed a crystalline nitride to be obtained at normal pressure. Nanocrystalline γ-Mo2N with an average particle size of 30 nm was obtained by reacting metallic sodium with anhydrous MoCl5 and NH4Cl in an autoclave at a temperature of 550°C [8]. Choi and Kumta [9] synthesized MoNx nanoparticles via ammonolysis
of molybdenum pentachloride in dehydrated chloroform for 8 h. Next, the solvent was evaporated at a temperature of 100°C in flowing dry ammonia. The reaction product was heat-treated at temperatures from 600 to 800°C in an ammonia atmosphere for 10 h. As the heat trea
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