Synthesis, characterisation and hydrogenation performance of ternary nitride catalysts

Abstract Synthesis of phase pure Co 3 Mo 3 N and Fe 3 Mo 3 N by temperature programmed ammonolysis has been established by XRD and elemental analysis. The ternary nitrides are characterised by a η-6 structure and low surface area (4–9 m 2  g −1 ). Pseudomorphic transformation of cobalt molybdate prepared using cobalt nitrate generated rod-shaped crystals while the use of iron chloride resulted in Fe 3 Mo 3 N aggregates with irregular morphology and wide size distribution. XPS measurements have revealed surface N enrichment relative to the bulk where the passivated samples show a range of oxidation states; Co 3 Mo 3 N exhibited Mo 2+ and Co n + (0 ≤  n  ≤ 3) whereas Fe 3 Mo 3 N was characterised by higher oxidation states (Fe 3+ and Mo 3+ ). Temperature programmed reduction (TPR) to 823 K served to remove the passivation layer where subsequent H 2 chemisorption and temperature programmed desorption (TPD) has demonstrated greater uptake on Fe 3 Mo 3 N relative to Co 3 Mo 3 N, resulting in a higher nitrobenzene hydrogenation rate (to aniline). Fe 3 Mo 3 N promoted selective reduction of –NO 2 in p -chloronitrobenzene to generate p -chloroaniline as sole product whereas Co 3 Mo 3 N favoured C-Cl scission with the formation of nitrobenzene (in addition to p -chloroaniline). Hydrodechlorination properties were further established for Co 3 Mo 3 N in the conversion of chlorobenzene (to benzene) under conditions where Fe 3 Mo 3 N was inactive. A temporal deactivation of both nitrides is associated with Cl poisoning of Co 3 Mo 3 N and structural changes to Fe 3 Mo 3 N.