Competitive hydrogenation and hydrodeoxygenation of oxygen-substituted aromatics over Rh/silica: catechol, resorcinol and hydroquinone

Kirkwood, K. and Jackson, S. D. (2021) Competitive hydrogenation and hydrodeoxygenation of oxygen-substituted aromatics over Rh/silica: catechol, resorcinol and hydroquinone. Topics in Catalysis, 64(17), pp. 934-944. (doi: 10.1007/s11244-021-01422-3)

Abstract

The competitive hydrogenation and hydrodeoxygenation (HDO) of dihydroxybenzene isomers, catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene) and hydroquinone (1,4-dihydroxybenzene), was studied in the liquid phase over a Rh/silica catalyst at 323 K and 3 barg hydrogen pressure. Under competitive hydrogenation conditions an order of reactivity of ortho > para > meta was observed. Catechol initially inhibited resorcinol and hydroquinone hydrogenation but not HDO suggesting separate sites for hydrogenation and HDO. When resorcinol and hydroquinone were reacted competitively, HDO became the favoured reaction. The data suggested that cyclohexane and cyclohexanone were primary products. At low dihydroxybenzene (DHB) conversion the ratio of HDO products was dependent upon DHB isomer. When all three DHB isomers were reacted together, initially 86% of the HDO yield came from catechol with the rest from hydroquinone. When resorcinol finally reacted, HDO products were produced first. Reaction of DHB isomers in pairs using deuterium instead of hydrogen revealed changes in kinetic isotope effect (KIE). The presence of competing reactants had a dramatic effect on the energetics of hydrogenation and HDO reactions of individual components, reinforcing the view that hydrogenation and HDO are mechanistically separate. This effect on reaction energetics observed when more than one substrate was present, highlights the limitations of studying one single model compound as a route to understanding the processes required for the upgrading of a true bio-oil feed.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Kirkwood, Miss Kathleen and Jackson, Professor David
• Authors: Kirkwood, K., and Jackson, S. D.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Topics in Catalysis
• Publisher: Springer
• ISSN: 1022-5528
• ISSN (Online): 1572-9028
• Published Online: 25 March 2021
• Copyright Holders: Copyright © 2021 The Authors
• First Published: First published in Topics in Catalysis 64(17): 934-944
• Publisher Policy: Reproduced under a Creative Commons license