Molybdena on silica catalysts: selective catalytic oxidation of ammonia to nitrogen over MoO₃ on siO₂ catalysts

MoO₃ on SiO₂ catalysts are suitable for the selective oxidation of ammonia into nitrogen (N₂) and water. The catalysts were prepared by homogeneous deposition precipitation using electrochemically reduced precursors. The experiments were carried out at atmospheric pressure and at temperatures ranging from 200 to 400 °C. Nitrogen and water yields of up to 100% at temperatures over 375 °C were obtained when ammonia and excess oxygen in helium were passed over a MoO₃ on SiO₂ catalyst. Catalysts containing less than 15 wt.% MoO₃ gave rise to no conversion of ammonia. The presence of small amounts of lead in the catalyst appeared to influence the conversion of NH₃ in a positive way. However, the presence of nitric oxide in the feed did not influence either the conversion of ammonia or the selectivity to nitrogen. The nitric oxide concentration remained constant during the conversion of ammonia. The results indicate that species reducible by hydrogen at 540 °C are related to the activity of the catalysts.