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Inhibiting the dealkylation of basic arenes during n-alkane direct aromatization reactions and understanding the C6 ring closure mechanism

Jarvis, Jack, Harrhy, Jonathan H., Wang, Aiguo, Bere, Takudzwa, Morgan, David John, Carter, James H., Howe, Alexander G. R., He, Qian, Hutchings, Graham J. and Song, Hua 2020. Inhibiting the dealkylation of basic arenes during n-alkane direct aromatization reactions and understanding the C6 ring closure mechanism. ACS Catalysis 10 , pp. 8428-8443. 10.1021/acscatal.0c02361
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Abstract

Pt/KL is the widely accepted catalyst for aromatizing n-hexane by 1,6 ring closure but encounters deactivation issues when aromatizing higher carbon-number feeds; undergoing extensive dealkylation to give unwanted CH4 and unselective products, as well as over-aromatization to form coke. Here, we report the use of a non-acidic MFI zeolite support, containing excess K+ beyond ion exchange capacity, well dispersed Pt, and high Pt presence inside the pores, for maximising direct n-alkane aromatization selectivity. TGA, catalyst deactivation studies, and characterizations show that the smaller pore sizes and lack of large cages in the MFI support sterically inhibit coke formation inside the pores (0% compared to 4.9% over Pt/KL for n-octane aromatization), which also reduces dealkylation of ethylbenzene and o-xylene under mild conditions to give a more selective product distribution, 86% selectivity by weight towards C6 ring closure compared to 27% for Pt/KL. Additionally, using NH3-TPD, XPS,CO-DRIFTS, and STEM, we show the contribution of excess K+ as an inhibitor of strong acid sites, an indirect Pt electron promoter through improving metal support interaction, and Pt dispersant. This work highlights the alternative use of well-understood zeolitic supports for the highly selective aromatization of n-heptane and n-octane by 1,6 ring closure, increasing the number of potential streams that can undergo direct aromatization, and providing a suitable alternative to Pt/KL.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Cardiff Catalysis Institute (CCI)
Publisher: American Chemical Society
ISSN: 2155-5435
Date of First Compliant Deposit: 13 July 2020
Date of Acceptance: 6 July 2020
Last Modified: 11 Sep 2020 09:11
URI: http://orca.cf.ac.uk/id/eprint/133364

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