McCullagh, A. M., Gibson, E. K. , Parker, S. F., Refson, K. and Lennon, D. (2023) The adsorption of nitrobenzene over an alumina-supported palladium catalyst: an infrared spectroscopic study. Physical Chemistry Chemical Physics, 25(38), pp. 25993-26005. (doi: 10.1039/D3CP03028H) (PMID:37729436)
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Abstract
As part of an on-going programme of development of an aniline synthesis catalyst suitable for operation at elevated temperatures, the geometry of the adsorption complex for nitrobenzene on a 5 wt% Pd/Al₂O₃ catalyst is investigated by infrared (IR) spectroscopy. Via an appreciation of the reduced site symmetry resulting from adsorption, application of the metal surface selection rule, and observation of in-plane modes only, the adsorption complex (Pd–nitrobenzene) at 28 °C is assigned as occurring vertically or tilted with respect to the metal surface, adopting Cₛσᵥ(yz) symmetry. Moreover, adsorption occurs via a single Pd–O bond. Single molecule DFT calculations and simulated IR spectra assist vibrational assignments but indicate a parallel adsorption geometry to be energetically favourable. The contradiction between calculated and observed structures is attributed to the DFT calculations corresponding to an isolated molecule adsorption complex, while IR spectra relate to multi molecule adsorption that is encountered during sustained catalytic turnover. Residual hydrogen from the catalyst reduction stage leads to aniline formation on the Pd surface at low nitrobenzene coverages but, on increasing nitrobenzene exposure, the aniline is forced on to the alumina support. A reaction scheme is proposed whereby the nitrobenzene adsorption geometry is inherently linked to the high aniline selectivity observed for Pd/Al₂O₃ catalysts.
| Item Type: | Articles |
|---|---|
| Additional Information: | The EPSRC are thanked for the provision of a PhD studentship (ALMcC, EP/R513222/1 and EP/N509668/1) |
| Keywords: | Nitrobenzene adsorption, alumina-supported Pd, adsorption geometry, vibrational spectroscopy. |
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Lennon, Professor David and Gibson, Dr Emma and Parker, Dr Stewart and Mccullagh, Miss Annelouise |
| Authors: | McCullagh, A. M., Gibson, E. K., Parker, S. F., Refson, K., and Lennon, D. |
| College/School: | College of Science and Engineering > School of Chemistry |
| Journal Name: | Physical Chemistry Chemical Physics |
| Publisher: | Royal Society of Chemistry |
| ISSN: | 1463-9076 |
| ISSN (Online): | 1463-9084 |
| Copyright Holders: | Copyright © 2023 The Owner Societies |
| First Published: | First published in Physical Chemistry Chemical Physics 25(38):25993-26005 |
| Publisher Policy: | Reproduced under a Creative Commons License |
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