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Title: Structure and Reactivity of Rhodium Promoted Heteropolyacid Catalysts
Author: Newman, Andrew D.
ISNI:       0000 0001 3443 4155
Awarding Body: University of York
Current Institution: University of York
Date of Award: 2007
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Acetic acid is an industrially important chemical with a worldwide demand in the region of 8 million tonnes p.a, over 80 % of which is currently generated via homogeneous methanol carbonylation using Rh or Ir catalysts and MeIi . Recent workii has shown systems combining rhodium and heteropolyacids (HPAs) to be active in the vapour phase carbonylation of methanol or dimethyl ether without a requirement for iodide, and at much milder conditions than existing technologies. However the catalysts rapidly deactivate, and little is known about the structurereactivity correlations or interaction between Rh, HPA and Si02 support. This work investigates the fundamental molecular properties of supported and rhodium-doped phosphotungstic acid catalysts, encompassmg catalyst preparation, activity and deactivation of both bulk and silica-supported Rh/HPA systems. The goal is to understand the operation and characteristics of these catalysts, and to explain and exploit their surprising activity towards methanol carbonylation at low temperatures and pressures. A range of surface and bulk analysis techniques have been employed both insitu and in the study of fresh and deactivated catalysts. The evolution of heteropolyacid on silica with increasing loading has been studied, correlating acidity and XPS measurements with activity in both a-pinene isomerisation and methanol condensation, Above 6.2 wt% catalysts have equivalent acidity, whilst a monolayer of26-44 wt% was most effective in non-polar reactions. Characterisation of rhodium during thermal treatment in reactive and inert atmospheres has been followed, revealing important insights into the composition and nature of deactivation of Rh/HPA/Si02 catalysts. Monolayer HPA/Si02 with -1 wt% Rh was found to be most effective, with diminishing benefit of increasing rhodium content. After initial deactivation, low conversion was sustained; product distribution and spent catalyst characterisation revealed rhodium reduction and agglomeration to be the cause of deactivation - reactivity in acid-only catalysed reactions was unaffected.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available