Title: Octane isomer dynamics in H-ZSM-5 as a function of Si/Al ratio: a quasi-elastic neutron scattering study

Authors (6): A. J. O'Malley, V. García-Sakai, N. Dimitratos, W. Jones, C. R. A. .Catlow, S. F. Parker

Themes: Circular Economy (2020)

DOI: 10.1098/rsta.2020.0063

Citations: 3

Pub type: article-journal

Publisher: The Royal Society

Issue: 2176

License: [{"URL"=>"https://royalsociety.org/-/media/journals/author/Licence-to-Publish-20062019-final.pdf", "start"=>{"date-parts"=>[[2020, 7, 6]], "date-time"=>"2020-07-06T00:00:00Z", "timestamp"=>1593993600000}, "delay-in-days"=>0, "content-version"=>"vor"}, {"URL"=>"https://royalsociety.org/journals/ethics-policies/data-sharing-mining/", "start"=>{"date-parts"=>[[2020, 7, 6]], "date-time"=>"2020-07-06T00:00:00Z", "timestamp"=>1593993600000}, "delay-in-days"=>0, "content-version"=>"tdm"}]

Publication date(s): 2020/07/24 (print) 2020/07/06 (online)

Pages: 20200063

Volume: 378 Issue: 2176

Journal: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences

Link: [{"URL"=>"https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2020.0063", "content-type"=>"application/pdf", "content-version"=>"vor", "intended-application"=>"text-mining"}, {"URL"=>"https://royalsocietypublishing.org/doi/full-xml/10.1098/rsta.2020.0063", "content-type"=>"application/xml", "content-version"=>"vor", "intended-application"=>"text-mining"}, {"URL"=>"https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2020.0063", "content-type"=>"unspecified", "content-version"=>"vor", "intended-application"=>"similarity-checking"}]

URL: http://dx.doi.org/10.1098/rsta.2020.0063

Dynamical behaviour of n- octane and 2,5-dimethylhexane in H-ZSM-5 zeolite catalysts of differing Si/Al ratios (15 and 140) was probed using quasi-elastic neutron scattering, to understand molecular shape and Brønsted acid site density effects on the behaviour of common species in the fluid catalytic cracking (FCC) process, where H-ZSM-5 is an additive catalyst. Between 300 and 400 K, n -octane displayed uniaxial rotation around its long axis. However, the population of mobile molecules was larger in H-ZSM-5(140), suggesting that the lower acid site concentration allows for more molecules to undergo rotation. The rotational diffusion coefficients were higher in H-ZSM-5(140), reflecting this increase in freedom. 2,5-dimethylhexane showed qualitative differences in behaviour to n -octane, with no full molecule rotation, probably due to steric hindrance in the constrictive channels. However, methyl group rotation in the static 2,5-dimethylhexane molecules was observed, with lower mobile fractions in H-ZSM-5(15), suggesting that this rotation is less hindered when fewer Brønsted sites are present. This was further illustrated by the lower activation barrier calculated for methyl rotation in H-ZSM-5(140). We highlight the significant immobilizing effect of isomeric branching in this important industrial catalyst and show how compositional changes of the zeolite can affect a range of dynamical behaviours of common FCC species upon adsorption. This article is part of a discussion meeting issue ‘Science to enable the circular economy’.

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