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

• Sequential approach for the catalytic removal of N2O and NOx using perovskite-type materials.
• Gain in activity toward N2O decomposition through perovskite reconstruction process.
• Redox thermal treatment of LaCo0.95Pd0.05O3 enhancing the stability of PdOx clusters at the surface.
• Importance of a pre-reductive thermal treatment on the nature of the Pt/LaFeO3 interface in the conversion of NO.
• Thermally stable growth of epitaxially oriented Pt particles providing synergistic effect on the activity.

A combined study was achieved to remove sequentially trace amounts of N2O 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 N2O decomposition and to enhance the usual low-temperature activity in NO conversion. The high-temperature catalytic decomposition of N2O was studied in the temperature range 500–700 °C in realistic conditions with 1000 ppm N2O, 5000 ppm NO, 6 vol.% O2, and 15% H2O. Starting from LaC0.95Pd0.05O3 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 PdOx clusters in strong interaction with the perovskite structure. A sharp increase in intrinsic rates and an apparent compensation effect emphasize the importance of the PdOx-support interface where Pd at the vicinity of anionic oxygen species from the perovskite can facilitate the formation of anionic vacancies potentially active for N2O dissociation. Regarding the NO/H2 reaction, Pt supported on LaFeO3 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–LaFeO3 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 dPt > 7.5 nm. On the other hand, for Pt particles with dPt < 7.5 nm, the NO/H2 reaction becomes more structure sensitive.

Figure optionsDownload high-quality image (70 K)Download as PowerPoint slide