Functionalized Composite Electrodes for Electrocatalytic Hydrogenation

1
Functionalized Composite Electrodes for
Electrocatalytic Hydrogenation
C. M. Cirtiu, N.-A. Bouchard, H.
Oudghiri-Hassani, P. A. Rowntree and H.
Ménard Département de Chimie, Université de
Sherbrooke, Sherbrooke, (QC), Canada, J1K 2R1
Introduction
Design and characterization of the catalyst
The aim of our research is to develop
intelligent electrodes that are able to make
use of molecular recognition at interface to
facilitate electrocatalytic hydrogenation
(ECH). The present study demonstrates that the
efficiency of the ECH process is related to the
controllable adsorption phenomena. A
functionalized surface can be obtained by in situ
adsorption of aliphatic carboxylic acids on the
catalyst matrix, adsorption which is supported by
energy considerations. These organically
functionalized materials promote the adsorption
of the target molecules under our experimental
conditions, and may permit the development of
selective ECH electrodes.
Electrocatalytic hydrogenation
Micrographics of the secondary electrons (1) and
cartography of the elements (2,3,4) for a ultra
thin cut of 10 Pd/Al2O3 catalysts
Alumina is able to adsorb the aliphatic acids and
to generate an organic monolayer on the surface
of the matrix (functionalization). This
functionalization can be carried out in situ in
the electrolysis cell.
The presence of the aliphatic acids adsorbed as
carboxylate on alumina is confirmed by DRIFT
spectra. This new organic phase is stable for
all temperature below to 200 ºC.
ECH results
Catalyst support
Organic phase nature
Aliphatic carboxylic acid is more strongly
adsorbed than phenol on catalyst (10
Pd/Al2O3). Functionalized alumina supported Pd
catalysts adsorb significantly more phenol than
a Pd unsupported catalyst. As predicted, the
aliphatic chains adsorbed on alumina also
influence the adsorption of phenol as the chain
lengthens, the adsorption is favoured. The ECH
efficiency increases with the length of the
aliphatic chain (butyric acid gt propionic acid gt
acetic acid). The presence of a co-solvent (MeOH)
modifies the polarity of the medium and also
influences the adsorption of the target molecule
to the functionalized catalyst surface this too
is predicted by the comparison with the reverse
phase chromatography.
Conclusions

• A new concept is presented here in situ
  functionalized materials for electrocatalytic
  hydrogenation processes.
• These new materials are based on the strong
  controllable adsorption of aliphatic carboxylic
  acids onto the catalyst support.
• This surface modification plays a key role in
  the adsorption/desorption phenomena of the target
  molecule onto catalyst surface.
• A direct correlation has been established
  between current efficiency and adsorption
  phenomena for the phenol ECH, under our
  experimental conditions.

Concentration of co-solvent (MeOH)
References  Modification of the surface
adsorption properties of alumina supported Pd
catalysts for the electrocatalytic hydrogenation
of phenol  Ciprian M. Cirtiu, Hicham Oudghiri
Hassani, Nicolas-A. Bouchard, Paul A. Rowntree
and Hugues Ménard, accepted for publication in
Langmuir
Acknowledgements We would like to thank Irène
Kelsey Lévesque (SEM analyses) Charles Bertrand
(TEM analyses) NSERC () FQRNT ()
This sequence is predicted if the functionalized
surface behave as a reverse-phase chromatographic
support
Ce 0.1 µmole mL-1 Q 100 C
The ECH efficiency depends on the adsorption of
phenol onto functionalized alumina catalyst
surface