LaNiO3 as a Pt catchment material in the ammonia oxidation process

Platinum is lost as gaseous PtO2 from the Pt-Rh (typically 95:5 wt%) catalyst used in the ammonia oxidation process. The most common technology utilized today for recovering PtO2 from the gas stream is to apply Pd-Ni (95:5 wt%) catchment gauzes. However, the technology suffers due to loss of Pd at the same time as a severe reconstruction of the alloy creates a large pressure drop during operation. In the search of alternative materials, LaNiO3 is considered as an interesting Pt catchment material. The evaluation is based on lab-scale Pt catchment experiments in a gas flow of dry air using a six-zone furnace with a Pt source placed at 1000 °C to create gaseous PtO2, and LaNiO3 pellets placed downstream at 700 – 900 °C. The duration of the experiments varied from 1 to 26 days, and scanning electron microscopy – energy dispersive X-ray analysis and powder X-ray diffraction were utilized to prove the catchment of Pt. The key finding is that LaNiO3 captures Pt and transforms via the non-stoichiometric rhombohedral LaNi1−xPtxO3 (x ≤ 0.075) and monoclinic La2Ni2−2xPt2xO6 (0.20 ≤ x < 0.50) perovskites into La2NiPtO6 (x = 0.50). Pt catchment is poor at 700 °C, but a substantial activity is documented at 800 and 900 °C. We furthermore demonstrate the recovery of Pt from the oxide by a wet chemical approach, and both LaNiO3 and La2NiPtO6 have been tested as potential catalysts for decomposition of NOx and N2O at relevant temperatures. LaNiO3 is not catalytically active in decomposition of NOx, the main ammonia oxidation products, while La2NiPtO6 has a minor catalytic activity toward NOx decomposition (1–2 %). However, both materials decompose the greenhouse gas N2O fully at 900 °C.