The surface chemistry of nanocrystalline MgO catalysts for FAME production: an in situ XPS study of H2O, CH3OH and CH3OAc adsorption

J.M. Montero, M.A. Isaacs, A.F. Lee, J.M. Lynam, K. Wilson*

*Corresponding author for this work

Research output: Contribution to journalSpecial issue

Abstract

An in situ XPS study of water, methanol and methyl acetate adsorption over as-synthesised and calcined MgO nanocatalysts is reported with a view to gaining insight into the surface adsorption of key components relevant to fatty acid methyl esters (biodiesel) production during the transesterification of triglycerides with methanol. High temperature calcined NanoMgO-700 adsorbed all three species more readily than the parent material due to the higher density of electron-rich (111) and (110) facets exposed over the larger crystallites. Water and methanol chemisorb over the NanoMgO-700 through the conversion of surface O2 − sites to OH and coincident creation of Mg-OH or Mg-OCH3 moieties respectively. A model is proposed in which the dissociative chemisorption of methanol occurs preferentially over defect and edge sites of NanoMgO-700, with higher methanol coverages resulting in physisorption over weakly basic (100) facets. Methyl acetate undergoes more complex surface chemistry over NanoMgO-700, with C–H dissociation and ester cleavage forming surface hydroxyl and acetate species even at extremely low coverages, indicative of preferential adsorption at defects. Comparison of C 1s spectra with spent catalysts from tributyrin transesterification suggest that ester hydrolysis plays a key factor in the deactivation of MgO catalysts for biodiesel production.

Original languageEnglish
Pages (from-to)170-178
Number of pages9
JournalSurface science
Volume646
Early online date14 Jul 2015
DOIs
Publication statusPublished - Apr 2016

Bibliographical note

-© 2015, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/

Funding: EPSRC (EP/F063423/1; EP/K000616/1; and Leadership Fellowship EP/G007594/4); and Royal Society for an Industry Fellowship (IF100206).

Keywords

  • biodiesel synthesis
  • ester
  • in-situ XPS
  • methanol
  • nanoparticulate MgO
  • solid base

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