Alkali metal doping of binary and ternary molybdenum nitrides for ammonia synthesis Rachel Young , Justin. S.J. Hargreaves University of Glasgow, UK Ammonia is a highly important feedstock due its use in synthetic fertilisers and potential as a fuel source. Despite the success of the Haber-Bosch process, the harsh conditions required (400-500 °C, 150 atm), requirement for steam reforming of methane to generate the hydrogen feedstock, and large industrial scale mean that the synthesis of ammonia consumes around 2 % of annual global energy demand. 1 In the search for a stable catalyst that is active under milder conditions, some great potential has been found in metal nitride catalysts, in particular, promoted ternary systems containing molybdenum. 2 Ternary materials are found to exhibit greater activity than their binary counterparts due to a scaling relationship, where one metal binds nitrogen very strongly and the other weakly, giving an intermediate binding strength which is more optimal for nitrogen adsorption. 3 The present work describes the preparation of the ternary nitrides Ni 2 Mo 3 N, Co3 Mo 3 N, and Fe 3 Mo 3 N via a sol-gel method. These materials, along with the binary β-Mo 2 N 0.78 species, have been tested for ammonia synthesis activity and the effects of promotion have been investigated via doping with alkali metal nitrates (KNO 3 or CsNO 3 ) between 0.2-5 wt% loading. The catalysts have also been tested for their lattice nitrogen reactivity, to investigate the possibility of a Mars-van Krevelen type mechanism occurring. References 1. The Royal Society. Ammonia: zero-carbon fertiliser, fuel and energy store. (2020). 2. Kojima, R. &; Aika, K. I. Cobalt molybdenum bimetallic nitride catalysts for ammonia synthesis: Part 1. Preparation and characterization. Applied Catalysis A: General 215, (2001). 3. Jacobsen, C. J. H. et al. Catalyst design by interpolation in the periodic table: Bimetallic ammonia synthesis catalysts [2]. Journal of the American Chemical Society vol. 123 (2001).
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