Synthesis, characterisation and hydrogenation performance of ternary nitride catalysts

• Application of Co and Fe ternary nitride in the hydrogenation of aromatic compounds.
• Fe3Mo3N exhibits greater H2 uptake and nitroarene hydrogenation rate.
• Co3Mo3N promotes the hydrodechlorination of p-chloronitrobenzene.
• Temporal deactivation accompanied by changes in surface composition.

Synthesis of phase pure Co3Mo3N and Fe3Mo3N 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 m2 g−1). Pseudomorphic transformation of cobalt molybdate prepared using cobalt nitrate generated rod-shaped crystals while the use of iron chloride resulted in Fe3Mo3N 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; Co3Mo3N exhibited Mo2+ and Con+ (0 ≤ n ≤ 3) whereas Fe3Mo3N was characterised by higher oxidation states (Fe3+ and Mo3+). Temperature programmed reduction (TPR) to 823 K served to remove the passivation layer where subsequent H2 chemisorption and temperature programmed desorption (TPD) has demonstrated greater uptake on Fe3Mo3N relative to Co3Mo3N, resulting in a higher nitrobenzene hydrogenation rate (to aniline). Fe3Mo3N promoted selective reduction of –NO2 in p-chloronitrobenzene to generate p-chloroaniline as sole product whereas Co3Mo3N favoured C-Cl scission with the formation of nitrobenzene (in addition to p-chloroaniline). Hydrodechlorination properties were further established for Co3Mo3N in the conversion of chlorobenzene (to benzene) under conditions where Fe3Mo3N was inactive. A temporal deactivation of both nitrides is associated with Cl poisoning of Co3Mo3N and structural changes to Fe3Mo3N.

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