Presented to The 2004 American Nuclear Society Winter Meeting Washington, D.C. November 14–18, 2004 Uranium-Based Catalyst M. J. Haire Nuclear Science and Technology Division S. H. Overbury, C. K. Riahi-Nezhad, and S. Dai Chemical Sciences Division Oak Ridge National Laboratory
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Presented to The 2004 American Nuclear Society Winter Meeting Washington, D.C. November 14–18, 2004 Uranium-Based Catalyst M. J. Haire Nuclear Science.
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Presented toThe 2004 American Nuclear Society Winter Meeting
Washington, D.C.November 14–18, 2004
Uranium-Based Catalyst
M. J. HaireNuclear Science and Technology Division
S. H. Overbury, C. K. Riahi-Nezhad, and S. DaiChemical Sciences Division
Oak Ridge National Laboratory
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Depleted Uranium (DU) as Catalysts
DU has proven active for many catalytic reactions Volatile organic compounds (VOCs) and chlorinated VOC oxidation Selective oxidation and ammoxidation (patented mixed U-Sb oxide) Partial oxidation—methane to methanol (patented mixed U-Mo oxide) Oxidative coupling (C chain lengthening) Selective catalytic reduction (SCR) of NO
Many other catalytic applications are possible (but unproven)
These reactions are important for many environmental applications and chemical production
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
New Synthetic Approaches
New techniques to improve catalyst performance and handling nanoporous supports by templating techniques co-assembly of U into nanoporous supports complexing U onto Si cubes
Techniques lead to high surface areas higher catalytic activity more efficient use of uranium dilutes specific radioactivity (dpm per gm material)
Convenient solid form sol-gel approach leads to monoliths easier handling before and after application reduced risk of loss of powder blow-out stabilize catalyst
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Synthesis of Nanoporous Materials Micelles of variable sizes
used as template molecules
TEOS produces Si gel around template molecules. Dope with uranium nitrate
alignment (crystallization) of micelles leads to ordered arrays
surfactant “burned out” or removed by solvent extraction
approach can be used to make mesoporous SiO2 or
TiO2, or other oxides Surfactant extraction or calcination
Silica condensation
Rodlike micelle
Silicate encapsulated micelles
TEOS(C16H33)N(CH3)3 Br
+ NaOH / H2O
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Nonpowder Forms of DU Catalysts
High Surface Area 250 m2/g monolithic catalysts
simplifies handling
uranium oxide is not co-precipitated; it is on/in the pore walls
transparency, possible photochemical processes
Reactive MembranesWavelength (nm)
350 400 450 500 550
Ab
so
rba
nc
e0.2
0.3
0.4
0.5
0.6
0.7
0.8
Optical AbsorptionSpectrum
Monolithic U-SiO2
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Reactor Set-up for Catalytic Testing
77 21
vent
GC/MS
Reactor (Temp. Controlled)
w/ quartz tube & sample
To Mass Spec/ G.C
bypass bypass
bubbler bubbler
bypass bypass
R R
21.0
Thermocouple
Bubbler and Ice Bath
Heating Zone
42
He O2 He
He gas for bubbler
Flow Regulator
Fro
m O
2 T
ank
Fro
m H
e T
ank
21 ml/min (He)
H2O
Syringe
Flow
Meter
He O
2(
77 m
l/m
in H
e +
42
ml/
min
O2 )
Mixing Point 140 ml/min
Pressure Gauge
Adjusting Valve
Bypass Flow Bypass Flow
Line to Bypass the Bubbler Line to Bypass the Reactor
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Photograph of ReactorUsed in DU Project
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Light-Off Curves to Compare Activity:U3O8
measure light-off curve to compare activity for toluene oxidation Reactor conditions
OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Activity for Oxidation of Other VOCs Chlorinated VOCs are common
pollutants at industrial and DOE sites
Uranium loaded TiO2 catalysts were active for destruction of chlorinated VOCs such as chlorobenzene and trichloroethylene (TCE) TCE and Cl-benzene are more
difficult to destroy
By-products are CO2 and water
mostly – but small amounts of benzaldehyde from Cl-benzene
Cl products are both HCl and Cl2
0
20
40
60
80
100
100 200 300 400 500Temperature (C)
Con
vers
ion
(%
)
toluene
TCE
chlorobenzene
U-meso TiO2
results of VOC combustion in absence of added water
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Comparison with Commercial Pt Catalysts
Uranium oxide in mesoporous support outperforms a Pt catalyst (0.1 wt % Pt on alumina) for comparable reaction conditions
T50 for TCE is more than 50°C lower for U-mTiO2 catalyst than for Pt catalyst
0
20
40
60
80
100
100 200 300 400 500 600Temperature (C)
Con
vers
ion
(%)
toluene
TCE
chlorobenzene
0.1 wt% Pt / Al2O3
0
20
40
60
80
100
100 200 300 400 500 600Temperature (C)
Con
vers
ion
(%)
toluene
TCE
chlorobenzene
U-meso TiO2
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Effect of Water Addition
In most applications water is present (e.g. soil vapor extraction wells for groundwater clean-up) Water does not interfere—
even enhances activity for TCE oxidation
Water permits higher HCl:Cl2 ratios of byproducts (good for most applications)
HCl by-product can be trapped
0
20
40
60
80
100
250 350 450 550Temperature ( C)
TC
E C
onve
rsio
n (%
)
dry
7 %
9 %
15 %
TCE oxidation by U-mesoTiO2
[H2O]
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Conclusions
Many DU based catalysts have been prepared and tested
A catalyst formulation based upon a titania-uranium (Ti-U) oxide (Ti:U = 1:20) was found to be competitive with noble metal catalysts for the oxidation of VOCs and chlorinated VOCs, e.g., toluene, Cl-benzene, TCE
The catalyst is stable to deactivation by Cl
The catalyst operates effectively in the presence of large amounts of water
Catalyst is suitable for destruction of VOCs emitted from soil vapor extraction wells, etc.