Transcript Electrodes of aluminium oxides functionalized containing

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).
2
CO2
4
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Mass Spectrometer Signal (a.u.)
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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
Al
10% Pd/Al2O3
Pd
O
0
(Heyrovsky reaction)
2 MHads ↔ 2 M + H2
(Tafel reaction)
ECH of unsaturated organic compound:

Y=Z + A ↔ (Y=Z)adsA
(Y=Z)adsA + 2MHads ↔ (YH-ZH)adsA

(YH-ZH)adsA ↔YH-ZH + A
DRIFT spectra of the Pd/Al2O3 catalyst aliphatic
acids modified: (a) - acetic acid; (b) - propionic
acid; (c) - butyric acid
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.
M – Pd, Pt, Ni, Rh, etc.
Hads – adsorbed hydrogen
A – catalyst matrix
Y=Z – unsaturated molecule
YH-ZH – saturated molecule
Y=Z
Y=Z
YH-ZH
H
Y=Z
Pd
H
H
Y=Z
H
organic
H chains
Catalyst support
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0,05
Current intensity: 20 mA
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-1
Q ads (mol g )
-1
Q ads (mole g )
0,9
Solvent: H2O / H2O – MeOH;
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Working electrode: CVR 100 ppi;
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0,0
Catalyst: 200 mg 10%Pd/Al2O3;
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1,1
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Phenol Concentration (%)
Electrolyte: 0.5 M organic acid buffer (pH=5);
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1,0
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Ce (mole mL )
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2,0
2,5
3,0
3,5
700
Organic phase nature
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1,1
1,0
600
This new organic phase is stable for all temperature
below to 200 ºC.
TEM image of a ultra thin cut of 10% Pd-alumina
catalyst (TEM Mag = 200000 x; HV= 80 kV)
ECH results
500
Pd
Alumina
Experimental conditions for ECH
400
The presence of the aliphatic acids adsorbed as
carboxylate on alumina is confirmed by DRIFT
spectra.
YH-ZH
H
H
300
Thermal analysis - mass spectroscopic data for
Pd/Al2O3 butyric acid modified catalyst (under Ar)
1,0
80
0,9
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-1
H3O+ + MHads + e- ↔ M + H2 + H2O
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Temperature (°C)
Q ads (mol g )
(Volmer reaction)
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Micrographics of the secondary electrons (1) and cartography of the elements (2,3,4) for a ultra thin cut of 10% Pd/Al2O3
catalysts
Hydrogen generation:
H3O+ + e- + M ↔ MHads + H2O
H2
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0,0
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1,5
2,0
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-1
Ce ( mol mL )
Charge (C)
Charge (C)
1,0
Phenol concentration: 8.8510-3 M;
Adsorption isotherms of (▲) phenol and (■) acetic
acid (pH=5) in water using 10% Pd-alumina supports.
T = 298 K;
Adsorption isotherms of phenol on: (■) – Pd 63
μm and (●) – 10% Pd/Al2O3 in 0.5 M acetic buffer
solution (pH = 5);
ECH of phenol in aqueous medium 0.5 M acetic buffer
(pH = 5); catalyst: (■) – Pd submicron; (●) – 10% Pd/Al2O3;
Adsorption isotherms of phenol on 10% Pd/Al2O3 in
water: methanol solution (80:20v/v) in the presence of
different electrolytes: (●) - acetic acid; (■) - propionic
acid; (▲) - butyric acid;
Aliphatic carboxylic acid is more strongly adsorbed than phenol on catalyst (10% Pd/Al2O3).
Electrochemical dynamic cell
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;
lengthens, the adsorption is favoured.
 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.
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.
0,06
Phenol Concentration (%)
Q ads (mol g )
-1
« Modification of the surface adsorption properties
of alumina supported Pd catalysts for the
electrocatalytic hydrogenation of phenol »
Ciprian M. Cirtiu, Hicham Oudghiri Hassani, NicolasA. Bouchard, Paul A. Rowntree and Hugues Ménard,
accepted for publication in Langmuir
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Kelsey
Lévesque
(SEM
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analyses)
Charles Bertrand (TEM analyses)
NSERC ($$$) & FQRNT ($$$)
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Ce (mol mL )
Adsorption isotherms of phenol on 10% Pd/Al2O3 in 0.5
M acetic buffer solution (pH = 5) for different
concentrations of co-solvent: (♦) – 0 % MeOH; (●) – 5 %
MeOH; (■) – 20 % MeOH; (▲) – 50 % MeOH; T = 323 K;
ECH of phenol in water: methanol solution (80:20v/v)
using different support electrolyte: (■) - acetic acid;
(●) - propionic acid; (▲) - butyric acid;
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50
40
30
20
20
Ce= 0.1 µmole
10
0,00
Irène
70
Charge (C)
0,01
We would like to thank:
80
10
Concentration of co-solvent (MeOH)
0,05
Acknowledgements
90
The ECH efficiency increases with the length of the aliphatic chain (butyric acid > propionic acid > acetic acid).
 A direct correlation has been established between current efficiency and adsorption
phenomena for the phenol ECH, under our experimental conditions.
References
100
Phenol Concentration (%)
 A new concept is presented here: in situ functionalized materials for electrocatalytic
hydrogenation processes.
Efficiency (%)
Conclusions
as the chain
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350
Charge (C)
ECH of phenol using different concentrations of
MeOH as co-solvent: (♦) - 0 % MeOH; (●) - 20 %
MeOH; (■) - 50 % MeOH; (▲) - 60 % MeOH; T = 298 K;
Q= 100 C
mL-1
10
0
0,000
0,005
0,010
0,015
0,020
-1
0,025
0,030
This sequence is predicted if the
functionalized surface behave as a
reverse-phase chromatographic support
Q ads (mol g )
The ECH efficiency depends on the
adsorption of phenol onto functionalized
alumina catalyst surface