Catalytic abatement of NO and N2O from nitric acid plants: A novel approach using noble metal-modified perovskites

A combined study was achieved to remove sequentially trace amounts of N 2 O and NO from nitric acid plants. Catalytic systems involving perovskite-type materials have been developed in which precious metals were incorporated in order to compensate deactivation processes for high-temperature N 2 O decomposition and to enhance the usual low-temperature activity in NO conversion. The high-temperature catalytic decomposition of N 2 O was studied in the temperature range 500–700 °C in realistic conditions with 1000 ppm N 2 O, 5000 ppm NO, 6 vol.% O 2, and 15% H 2 O. Starting from LaC 0.95 Pd 0.05 O 3 prepared by a sol gel route, it was found that appropriate sequential oxidative/reductive pre-activation thermal treatments can lead to the diffusion and the segregation of PdO x clusters in strong interaction with the perovskite structure. A sharp increase in intrinsic rates and an apparent compensation effect emphasize the importance of the PdO x -support interface where Pd at the vicinity of anionic oxygen species from the perovskite can facilitate the formation of anionic vacancies potentially active for N 2 O dissociation. Regarding the NO/H 2 reaction, Pt supported on LaFeO 3 shows remarkable activities below 100 °C depending on the temperature of the pre-reductive thermal treatment and the aging process at 500 °C in reaction conditions. Activity in NO reduction at 80 °C has been explained from the involvement of the Pt–LaFeO 3 interface supported by HRTEM observations relative to the growth of epitaxially orientated Pt particles and the correlation observed between calculated rates based on the length of the interfacial perimeter increasing with the particle size diameter. Such a trend persists at higher temperature ( T  = 255 °C) when d Pt  > 7.5 nm. On the other hand, for Pt particles with d Pt 2 reaction becomes more structure sensitive.