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Uranium-Based Catalyst

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U. S. DEPARTMENT OF ENERGY. Depleted Uranium (DU) as Catalysts ... U. S. DEPARTMENT OF ENERGY. Effect of Uranium Loading in TiO2 Based Mesoporous Catalysts ... – PowerPoint PPT presentation

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Title: Uranium-Based Catalyst


1
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
Presented to The 2004 American Nuclear Society
Winter Meeting Washington, D.C. November 1418,
2004
2
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 oxidationmethane 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

3
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

4
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

TEOS
(C16H33)N(CH3)3 Br NaOH / H2O
Silicate encapsulated micelles
Rodlike micelle
Surfactant extraction or calcination
Silica condensation
5
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 Membranes

Monolithic U-SiO2
6
Reactor Set-up for Catalytic Testing
Line to Bypass the Bubbler
Line to Bypass the Reactor
Bypass Flow
Bypass Flow
Mixing Point 140 ml/min
bypass
bypass
( 77 ml/min He 42 ml/min O2 )
vent
bypass
bypass
Adjusting Valve
bubbler
bubbler
Pressure Gauge
GC/MS
R
R
Heating Zone
Thermocouple
21 ml/min (He)
O2
He
To Mass Spec/ G.C
Flow Regulator
He O2 He
77
21
42
H2O Syringe Flow Meter
21.0
From O2 Tank
From He Tank
Bubbler and Ice Bath
Reactor (Temp. Controlled)
w/ quartz tube sample
He gas for bubbler
7
Photograph of Reactor Used in DU Project
8
Light-Off Curves to Compare ActivityU3O8
  • measure light-off curve to compare activity for
    toluene oxidation
  • Reactor conditions
  • 25 mg catalyst
  • He flow 150 cm3/min
  • O2 flow 40 cm3/min
  • toluene 500 ppm
  • GHSV 72000 hr-1
  • Mesoporous silica (MCM-41) without DU is inactive
  • U3O8 obtained by calcination of UO2(NO3)2
  • Pure U3O8 is active but low surface area (lt0.1
    m2/g )

9
U impregnated in Mesoporous Support
  • U-MAS-5
  • UO2 (NO3)2 impregnated into solid mesoporous
    silica
  • silica contains 5 Al
  • USi 110
  • improved light-off compared to pure U3O8

10
Catalysts Synthesized by Co-Synthesis Techniques
  • U-SiP123 catalysts
  • Uranium nitrate put into synthesis mixture
  • Pluronic P123 (EO-PO-EO triblock co-polymer)
  • Acid conditions
  • Vary USi ratio
  • 50 conversion above 450?C
  • Activity higher than U3O8 although lower U
    concentration
  • Gave poorly ordered mesopores
  • Broad BJH pore distribution
  • BET SA 225300 m2/g

11
TEM Characterization of DU Catalysts
  • Catalyst particle of U-MAS-5
  • Al3 doped silica mesoporous support impregnated
    with uranyl nitrate
  • Calcined 900ÂșC
  • High resolution TEM using HD-2000 at ORNL
  • Uranium oxide particles located within pores

12
STEM Micrograph of DU Catalyst
  • Catalyst U-SiF127
  • UO2 (NO3)2 mixed in with TEOS
  • Pluronic F127 (EO-PO-EO triblock co-polymer)
  • Acid conditions
  • U part of the Si walls
  • USi 120
  • Mesoporous structure shows as parallel walls
  • Pore spacing 10.3 nm
  • Uranium oxide particles are uniformly sized
  • lt1015 nm

13
X-ray Diffraction of DU Catalysts
  • XRD permits identification of phases present in
    catalyst before or after reaction
  • U-meso-8
  • USi 110
  • Poor activity
  • UO2 and U3O8 present
  • U-meso-6
  • USi 120
  • Good activity
  • Only U3O8 present
  • XRD shows that U3O8 is the most active phase
  • Cause of UO2 growth in U-meso-8 not clear

14
Promotion of Uranium CatalystsEffects of
Potassium Addition
  • Potassium is frequently used as promoter in many
    catalysts
  • Idea Promote Cl-C bond cleavage by K addition
  • Method 1 co-assembly including K salts
  • Br, Nitrate or oxalate salts
  • USi120
  • UK 11
  • Surface area and pore structure collapses
  • Surface area drops from 190 m2/g to 1-5 m2/g
  • loss of activity
  • Method 2 sequential impregnation of MCM-41 with
    uranyl nitrate and K salts
  • Surface area drops from 760 to 26 m2/g
  • loss of activity

15
Promotion of Uranium CatalystsEffects of K, Ca
Fe Oxide Additions
  • Try other components for urania catalysts
  • Co-assembly with FeNO3 and Mg acetate (Ca
    nitrate)
  • Surface area remains high
  • Pore structure good
  • But, no enhancement of activity

16
Effect of Uranium Loading in TiO2 Based
Mesoporous Catalysts
  • Get optimal activity at 5 mole U (UTi120)
  • Surface area (and activity) affected by
    calcination temperatures

Toluene oxidation
17
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

results of VOC combustion in absence of added
water
18
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 50C lower for U-mTiO2
    catalyst than for Pt catalyst

19
Effect of Water Addition
  • In most applications water is present (e.g. soil
    vapor extraction wells for groundwater clean-up)
  • Water does not interfereeven enhances activity
    for TCE oxidation
  • Water permits higher HClCl2 ratios of byproducts
    (good for most applications)
  • HCl by-product can be trapped

20
Conclusions
  • Many DU based catalysts have been prepared and
    tested
  • A catalyst formulation based upon a
    titania-uranium (Ti-U) oxide (TiU 120) 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.
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