Inelastic neutron scattering and heterogeneous catalysis:

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Inelastic neutron scattering and heterogeneous
catalysis methanol on ?-alumina.
David Lennon Department of Chemistry University
of Glasgow
Coeseners House, November 2008.
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1. Introduction

• Characterization of surface acidity for modified
  aluminas.
• Target reaction
• CH3OH CH3OH ? CH3OCH3 H2O
• Part of a wider programme seeking to develop
  structure/ activity relationships for a new
  generation of methyl chloride catalysts.

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TOSCA Pyridine on ?-alumina

• New information on surface Lewis acidity

Lundie et al, J.Phys.Chem.B, 2005
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Four-Site Model
adsorption site
Lundie et al, J.Phys.Chem.B, 2005
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?-Alumina/methanol - DRIFTS

• Unknown band at 2600 cm-1.

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?-Alumina/methanol - Transmission IR spectroscopy
Band actually present in literature spectra but
not assigned.
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?-Alumina/methanol DRIFTS - saturated overlayer
heated to 473 K for 15 mins.

• Unassigned feature clearly present.

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TOSCA. Methanol, chemisorbed overlayer, model
compound.

• Methyl rock now accessible. Methoxy?

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Energy minimised structure for methoxy on
?alumina (110).
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Experiment vs simulated INS spectra methoxy on
?alumina.
Reasonable correlation but simulations
compromised by complexity of surface.
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INS cell as a batch reactor (TOSCA)
INS capable of following molecular transformation.
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MARI. Ei 4034 cm-1

2600 cm-1 feature assigned to a combination of
methyl rock and methyl deformation mode
(117014602630cm-1).
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• INS Intensity-
• Q momentum transfer, ? energy of vibration, ?
  cross section, U? root mean square displacement
  of atoms in the mode, exponential term
  Debye-Waller factor, UT total root mean square
  displacement of all the atoms in all the modes.

• MARI - Scattered intensity as a function of
  collection angle determines momentum transfer.
  Potentially valuable tool for distinguishing
  fundamental modes.

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The more general form of S(Q,n?) is
n specifies nature of vibrational transition. By
differentiation, the maximum in S(Q,n?) ,occurs
when
thus providing a method to distinguish
fundamentals (n 1) from higher order (n ³ 2)
transitions such as overtones and combinations.
Parker et al, JACS, 2004.
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MARI ?-alumina/methanol mitre plot.

• Permits mapping of neutron scattering intensity
  with energy and momentum transfer.

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Chemisorbed methanol momentum transfer
dependence.

• Red ?(C-H) Blue ?(C-H) Purple 2630 cm-1.

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Al(OCH3)3 momentum transfer dependence.

• Red ?(C-H) Blue ?(C-H) Purple 2630 cm-1
  Green ?(C-H).

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McInroy et al, Langmuir, 2005
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Methanol Adsorption -DME TPD

• Minimisation of by-product formation by control
  of surface acidity.
• New catalyst now used in the industrial
  reactors.

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SUMMARY (1)

• DRIFTS of Al2O3/CH3OH revealed previously
  unreported feature. New surface species?
• INS increased dynamic range accessible for active
  catalyst.
• 2600 cm-1 feature assigned to combination of
  methyl rock and deformation modes. No new
  species.

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SUMMARY (2)

• Momentum transfer dependence (MARI) confirmed
  2600 cm-1 to be a non-fundamental mode.
• Mechanism developed for Al2O3/CH3OH system.
• Catalyst preparation modified to control DME
  production.
• Laboratory concept ? large-scale commercial
  operation.

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7. Acknowledgements

• David Lundie University of Glasgow
• Alastair McInroy University of Glasgow
• John Winfield University of Glasgow
• Stewart Parker ISIS Facility, RAL.
• Peter Jones INEOS Chlor Ltd.
• Chris Dudman INEOS Chlor Ltd.
• INEOS Chlor Ltd.
• EPSRC//Royal Society/SHEFC.
• ISIS Facility, Rutherford Appleton Laboratory.

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