CATALYTIC ETHANOL STEAM REFORMING Am. Chem. Soc., Div. Pet. Chem. 2008, 51 p.1&2 M. Scott B.Sc....
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Transcript of CATALYTIC ETHANOL STEAM REFORMING Am. Chem. Soc., Div. Pet. Chem. 2008, 51 p.1&2 M. Scott B.Sc....
CATALYTIC ETHANOL STEAM REFORMING
a
b
cO
CH2
CH3
O
CH2
CH3
O
CH2
CH3
a
b
cO
CH2
CH3
O
CH2
CH3
O
CH2
CH3
Am. Chem. Soc., Div. Pet. Chem. 2008, 51 p.1&2
M. Scott B.Sc. M.Sc.(hons)Department of ChemistryThe University of Auckland
Handbook of Green Chemistry, Wiley 2008
Topics in Catalysis, in press
Science, in press
Renewable energy cycle
Photosynthesis 2807 kJ/mol
C6H12O6 Glucose
H2 combustion-286 kJ/mol
Fermentation 15 kJ/mol
Steam reforming 173 kJ/mol
6CO2 + 12H2
+ O2
+ H2O
2CH3CH2OH + 2CO2
Ethanol
+ hν
6CO2 + 12H2O
∆
The catalyst
• Cerium dioxide nanoparticles as the supporting material.
• Rhodium metal dissociates sp3 C-H bond• Rh/CeO2 dissociates C-C bond of ethanol
• Palladium excels in hydrogenation and oxidation
Bimetallic Rh,Pd/CeO2 displays ideal properties
Steam ReformingAn activated process
298K; Ethanol on reduced Rh/CeO2
J. Catal. 208, 393-403 (2002)
CH3CH2O Ce
H2C
CH2OCe Rh
H2C
CH2OCe Rh
CH4 + CO + H2
CH3CH2O CeCH3CH2OH
CO
Catalyst manufacture
Ce3+(NO3)3.6H2O Ce4+(OH)4.xH2O
Precipitation
Deposition
CeO2 nano-particles
pH 9
Ce4+(OH)4.xH2O CeO2
RhCl3(aq) Rh3+
PdCl2(aq) Pd2+
773 K
Catalytic testing• 6:1 water to ethanol ratio shows
higher CH4 conversion than 3:1 ratio => higher H2 vol. %
• Effects of varying reaction temperature
• Effects of varying weight percentage loading noble metal
• Varying throughput (2.5, 5, 6.5 and 11.5 mL/hour)
0
10
20
30
40
50
60
70
80
90
100
Mol
ar S
elec
tivity
493 540 596 643 697 737 789 843
Temperature (K)
Selectivity vs Temperature (6:1)
CH3CH2OH → CH4 + CO + H2 ΔH0 = 50 kJ/mol
CO + H2O → CO2 + H2
ΔH0 = -41 kJ/mol CH4 + 2H2O → CO2 + 4H2
ΔH0 = 164 kJ/mol
Temperature dependence
Temperature Programmed Desorption
Water
CH3CH2-
Acetaldehyde
Acetaldehyde
CH3
CH4
CO
CH3CH2-
CeO2
500K & 773K
1%Pd,1%Rh/CeO2
375K & 525K
CO2
CO2
Effect of metal loading11.5 mL/hour, 6:1 and 773K
wt.% on ceria
Vol.%
H2
Vol.%
CO2
Vol.%
CH4
Vol.%
CO
Χ % max.
H2 yield
1%Pd 74 22 2 2 0.24 24
1%Rh 59 23 15 3 0.77 61
½%Rh, ½%Pd 63 24 11 2 1 84
½%Rh, 1%Pd 69 17 9 5 0.56 51
½%Rh, 2%Pd 75 18 5 2 0.12 12
Transmission Electron Microscopy
Pd,Rh alloy
Used catalyst Used catalyst
•Alloying of Rh and Pd
•Reduction of Rh2O3
•Restructuring of Support
•Origins at interface
•Lowering CN of Cerium
• Rh/CeO2 based catalyst
• Bimetallic catalyst very active
• Low metal loadings show best activity
• Active sites at Rh-Ce and Pd-Ce interface
• High temperature required for CH4 oxidation
• CH4 reforming and CO oxidation inadequate
• Dramatic restructuring occurring
• Activation of catalyst occurring
• No signs of deactivation
CH3CH2OH + 3H2O → 6H2 + 2CO2∆H=173 kJ/mol
Future research
• In situ FTIR• TPD studies• Further XPS studies• Near Edge X-ray Absorption Fine Structure • Further PAS and TEM• Maximise outflow• Doping• ⅓wt.%Rh,⅓wt.%Pd,⅓wt.%Ni/Ce0.75Zr0.25O2
Inverse Opal Ceria
20000x
100000x
Scanning Electron MicroscopyTransmission Electron
Chem. Mater. 2008, 20, 1183–1190
Microscopy
•3D macroporous structure
•Resistant to sintering to 1073K
•Allow gas low through pores
•High surface to volume ratio
Acknowledgments:Associate Professor Hicham IdrissSupervisor
Dr Geoffrey Waterhouse,Dr William Chiu, Dr Maria GoeffreyUniversity of Auckland Graduates
Alister Gardiner and Simon Arnold Industrial Research Limited, Christchurch
Professor Jordi Llorca (HRTEM)Universitat Politècnica de Catalunya, Barcelona, Spain
Dr Steven J. Pas (PAS) Commonwealth Scientific and Industrial Research Organisation (CSIRO) Manufacturing and Materials Technology, Victoria, Australia
Mark Blackford (TEM)Australia’s Nuclear Science and Technology Organisation, Lucas Heights, Sydney, Australia
XPS 1%Rh,1%Pd/CeO2 and PAS1 Ethanol + 3 water at 773 K, 3 hours at ca. 100 Torr
880890900910920
Binding Energy (eV)
Co
un
ts p
er s
eco
nd
(arb.
Un
its)
vo
v
v’
v’’v’’’u
u’u’’u’’’
XPS Ce3d5/2,3/2 Rh-Pd/CeO2
Ce3+
Fresh
Used
EB = hν – (φ + EK)
Voids in the bulk
PAS 2%Rh,2%Pd/CeO2
•Oxidation of CeO2
•Reduction of metal
•Homogenization
•Growth of voids