Davies, G., Driver, J., Ward, A. et al. (2 more authors) (2021) Operando studies of aerosol-assisted sol-gel catalyst synthesis via combined optical trapping and Raman spectroscopy. Journal of Physical Chemistry C, 125 (41). pp. 22591-22602. ISSN 1932-7447
Abstract
New insights have been gained into chemical transformations occurring in the initial stages of aerosol-assisted sol–gel (AASG) synthesis of catalysts. This has been achieved through the combined application of optical trapping and Raman spectroscopy. AASG is an emerging technology in catalyst manufacturing that presents numerous advantages over conventional approaches, including the ability to access unique catalyst morphologies. However, the processes occurring during synthesis are largely inferred from bulk-phase analyses due to challenges in conducting in situ or operando measurements on moving aerosols within a flow tube. Herein, these obstacles are overcome through Raman spectroscopic interrogation of a single aerosol droplet constrained within an optical trap, which acts as a direct analogue for a particle moving along a flow tube. These studies represent the first operando investigations of AASG synthesis. The synthesis of Ni/Al2O3 catalysts has been studied, with spectroscopic interrogation conducted on each component of the precursor synthesis solution, where possible, up to and including a mixture containing all components necessary for catalyst synthesis. Raman spectroscopy confirms the formation of stable self-assembled macrostructures within the aerosol and provides direct insights into the reaction mechanisms. Crucially, evidence was obtained allowing alternative reaction pathways to be postulated within the confined environment of an aerosol droplet in comparison to bulk-phase syntheses. In aerosols where nickel was not present, but contained all other components, isothermal room-temperature studies showed the formation of stable but unreactive droplets of ∼1 μm, which were proposed to contain micelle-type structures. Upon heating, initial gelation transformations were seen to be achieved at temperatures higher than ∼56 °C. Notably, little loss of spectral intensity corresponding to the C–H stretch (ethanol) was observed from the heated aerosol, implying that evaporation is not a prerequisite for the reaction. When nickel is present in the synthesis solution reactive transformations occur at room temperature, proposed to result in a continuous Al–O–Ni–NO3 structure; a more rapid transformation takes place at elevated temperatures. These results provide the first direct evidence of the processes occurring within aerosols during AASG and shed new light on the mechanistic understanding of this technology. This therefore facilitates the design of new synthetic approaches and hence the production of catalysts and other materials with enhanced properties.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2021 American Chemical Society. This is an author-produced version of a paper subsequently published in Journal of Physical Chemistry C. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | Optical tweezers; heterogeneous catalysis; vibrational spectroscopy; sol-gel materials synthesis; aerosol |
Dates: |
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Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) > Department of Chemical and Biological Engineering (Sheffield) |
Funding Information: | Funder Grant number Science and Technology Facilities Council 15230014 McGregor Engineering and Physical Sciences Research Council 1952546; EP/R026815/1 |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 11 Oct 2021 11:23 |
Last Modified: | 13 Oct 2022 00:34 |
Status: | Published |
Publisher: | American Chemical Society |
Refereed: | Yes |
Identification Number: | 10.1021/acs.jpcc.1c07517 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:178719 |