Issue 24, 2022

Aging of industrial Fe-zeolite based catalysts for nitrous oxide abatement in nitric acid production plants

Abstract

The influence of hydrothermal aging on the structural and catalytic properties of two commercial Fe-exchanged zeolite catalysts (Fe-FER and Fe-ZSM-5) in the extruded form employed for the removal of N2O from the exhaust of nitric acid production plants has been investigated. Catalytic experiments showed that N2O conversion was retained on Fe-FER while it was totally lost on Fe-ZSM-5, which promoted N2O formation under reaction conditions of selective catalytic reduction of NOx with NH3 (SCR). Combining data from several characterization techniques, we were able to identify a unique difference in the aging behaviour of the two catalysts. Irrespective of the catalyst, 27Al and 29Si-MAS NMR spectroscopy demonstrated significant loss of framework Al. NH3-TPD experiments corroborated the NMR results indicating a remarkable loss of NH3 storage capacity, especially at the expense of the Brønsted acidity. In contrast, UV-vis and X-ray absorption spectroscopy showed that the two catalysts experienced opposite behaviour with respect to the evolution of Fe species upon aging. Fe-ZSM-5 suffered from Fe agglomeration, while Fe species experienced re-dispersion in Fe-FER. These results indicate that the aging treatment of the Fe-exchanged zeolite catalysts does not inevitably lead to the agglomeration of isolated Fe sites. Hence, Fe-ZSM-5 develops into a less selective catalyst, promoting N2O formation through the undesired nonselective NH3 oxidation. Differently, this Fe-FER retains its catalytic activity and becomes less active towards NH3 oxidation. The results of our characterization and catalytic activity study could be of relevance for the selection of Fe-zeolite-based catalysts for this type of application. Furthermore, our investigation provides evidence that the fate of extra-framework Fe species under hydrothermal aging cannot be thoroughly described just by an agglomeration phenomenon.

Graphical abstract: Aging of industrial Fe-zeolite based catalysts for nitrous oxide abatement in nitric acid production plants

Article information

Article type
Paper
Submitted
22 avg 2022
Accepted
28 okt 2022
First published
31 okt 2022

Catal. Sci. Technol., 2022,12, 7308-7321

Aging of industrial Fe-zeolite based catalysts for nitrous oxide abatement in nitric acid production plants

F. Buttignol, D. Rentsch, I. Alxneit, A. Garbujo, P. Biasi, O. Kröcher and D. Ferri, Catal. Sci. Technol., 2022, 12, 7308 DOI: 10.1039/D2CY01486F

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