7. berman - molecular
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MOLECULAR DYNAMICS &THEORETICAL CHEMISTRY17 March 2011
MICHAEL R. BERMANProgram Manager
AFOSR/RSA
Air Force Office of Scientific Research
AFOSR
Distribution A: Approved for public release; distribution is unlimited. 88ABW-2011-0801
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2011 AFOSR SPRING REVIEW2303E PORTFOLIO OVERVIEW
NAME: Michael Berman
BRIEF DESCRIPTION OF PORTFOLIO:Research on understanding and exploiting chemical reactivity andenergy flow in molecules to improve Air Force systems, processes,and materials.
Understanding and exploiting chemical reactivity and catalysis forimproved storage and utilization of energy
LIST SUB-AREAS IN PORTFOLIO:Molecular DynamicsTheoretical Chemistry
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Challenges in Chemical DynamicsMolecular Dynamics, Theoretical Chemistry, Nanoenergetics
Energetic Materials (Rocket propellants, explosives) Energetic ionic liquids CHNO limit; new approaches Energetic nanostructures Sensitivity, mechanisms Non-traditional concepts Safer, penetrating munitions
Atm/Space Chemistry (Signatures, surveillance) Upper atmosphere, space Hypersonic prop, gas/surf interact. Signatures & backgrounds Rates/mech. of ion-molecule procs. Ion & plasma processes Predictive codes, communication
Nanostructures/Sensors (Catalysis, Sensing)
Nanostructures for catalysis
Atomic scale imaging and control Surface-enhanced detection Size-dependent properties
Lasers and Diagnostics (Infrared lasers, missile defense) High-Power Gas Lasers Efficient pumping, energy transfer Novel analytical tools/methods Relaxation processes
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Scientific Challenges
Control and Imaging of Catalysis Understanding of mechanisms new dimensions in catalysis
Bringing together new developments in ability to:
Prepare
Probe
Predict
the properties, reactions, and interactions of nanostructures
Makes prohibitively slow processes practical
Catalysis is key to energy storage and fuel production
Important practical military and industrial impacts
Co-catalysts, promoters, substrates, new materials,
Plasmonics Exploit high local E fields; novel sensing
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Transformational Opportunities
Secure, sustainable energy supply
CO2 JP8
Endothermic Fuels for cooling high-speed vehicles
Mission enabled by catalysis
Dual mode propellants for satellites
Ionic liquids for main thrusters and station keeping
http://www.fairchild.af.mil/shared/media/photodb/photos/040816-F-4884R-002.jpghttp://www.google.com/imgres?imgurl=http://images.clipartof.com/small/14151-Wind-Turbines-On-A-Hill-Generating-Electricity-Poster-Art-Print.jpg&imgrefurl=http://www.clipartof.com/interior_wall_decor/details/Nuclear-Fossil-Fuel-Wind-Power-Photovoltaic-Cells-And-Hydro-Electric-Water-Power-Generation-Farms-Poster-Art-Print-40385&usg=__Z5cVVX2-1DCHVXbyX__PxTUGtPM=&h=356&w=450&sz=47&hl=en&start=6&zoom=1&um=1&itbs=1&tbnid=2pjYIfasuxROAM:&tbnh=100&tbnw=127&prev=/images%3Fq%3Dwind%2Bpower%2Bclip%2Bart%26um%3D1%26hl%3Den%26sa%3DX%26tbs%3Disch:1&ei=jkNKTa4GgfuXB-OQkPMP -
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Research Environment: Other Orgs.That Fund Related Work
NSF Covers all areas of chemistry Center on Powering the Planet (water splitting)
DoE Basic Energy Sciences Hub on Solar Fuels
From research to industrial production Transition mechanism Congressional line item
AFOSR research funds fundamental, underpinningwork on understanding catalytic mechanisms
Use tools of physical chemistry to probe catalytic mechanisms
Active sites, size-selected clusters, role of local environment
Ways to control catalysis: mixed metals, substitutes for rare matls
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Program Trends
Catalysis
Sustainable Energy
Small Molecule Activation
Ionic Liquid Propellants
Plasma / Ion Chemistry/Interfaces
Hybrid Chemical Lasers
Sensors for Trace Detection
Modeling of Material Properties
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Recent Transitions
Al-cluster based energetics(Bowen, Johns Hopkins; Castleman, Penn St.) Funding from DTRA, ONR
NSWC, Indian Head (Jim Lightstone)
First materials produced in apparatus
Atomic Layer Deposition / Molecular Layer Deposition(George, Colorado)
ALD gas diffusion barrier technology is beingdeveloped actively by DuPont
ALD on polymers of Copper-Indium-Gallium-Selenide(CIGS) for flexible solar photovoltaic cells
ALD of Al2O3 best deposition method for pinhole anddefect free coatings prevents O2/H2O penetration
(Al2O3 ALD coating of 10 nm provides barrier equal to glass)
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Carbon-Neutral Fuels: ConvertingCarbon Dioxide to Fuels
Objective:
Produce energy dense hydrocarbonsand alcohols using CO2 as a feedstock
Approach:
Develop new electrocatalysts toefficiently produce alcohols andcarbon-carbon bonded products fromCO2 and sunlight feedstocks
Identify key mechanisms anddynamics related to the necessarymultielectron processes.
Blue light (465nm) is used toconvert CO
2
toalcohols with asubstitutedpyradine catalystand a p-GaPelectrode
Prof. A. Bocarsly
Payoff: A secure and sustainable sourceof liquid fuels for aircraft use
A carbon neutral fuel CO2produced in combustion is offsetby using CO2 as a feedstock
Solar fuels store the energy from the sun in energy-
dense chemical bonds for use as transportation fuel.
Key intermediate in pyridiniumcatalysis of CO2reduction
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Isolation of Key Intermediate inCO2 Reduction Process
Photoelectrochemical conversion of CO2 to fuels using pyridine as a catalyst
Isolation of key carbamate radical anion intermediate in a supersonic expansion byreaction of pyridine and (CO2)nclusters
IR spectra confirms proposed mechanism involving the formation of a covalentbond between CO2 and pyridine
1000 1200 1400 1600 1800 2000 2200 2400
Predis
s.Yield
Photon Energy, cm-1
New C-N covalent
bond formation
Johnson and co-workers, Yale University
JACS Communication, 132, 15508 2010.
Transfer rxn components fromsolution to the gas phase usingnon-destructive ionization methods
Exploit recent advances incryogenic ion chemistry to quench
reaction intermediates into cold,stable complexes
Structurally characterized with highresolution infrared spectroscopy
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New Electrocatalytic Process forCO2 Reduction Observed by SHG
Wasted energy in CO2 reductiondue to large overpotential
Room-Temperature Ionic Liquid(RTIL) forms stable complex with
CO2-
on Pt surface and reversiblycatalyzes CO2 to CO conversion
Process observed with compactbroadband SFG spectrometerutilizing femtosecond IR pulses to
obtain spectra at electrode-electrolyte interfaces
Dlott, Masel, U Illinois Urbana-Champaign
Potential cyclesfrom 0.5 to -1.4 Vvs SHE showgradual buildup of
CO on surface
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Plasmon-Resonant Enhancement ofPhotocatalytic Water Splitting
Photodriven splitting of water toH2 and O2 on TiO2 substrates isgreatly enhanced (x66) by thepresence of Au nanoparticles.
Use highly catalytic TiO 2 with
highly plasmonically active Aunanoparticles
Local E-field enhancement nearthe TiO2 surface increaseselectron-hole pair generation at
the surface of the TiO2 Larger enhancement factors
possible if this mechanism canbe optimized.
Cronin, U Southern California
Nanoletters, 2011
Fuel Cooling Technologies Enable Hypersonic Systems
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New fuel-cooling technologies will increase reliability of hypersonic demonstrators, and arerequired for longer duration, higher Mach number hypersonic vision vehicles.
Fuel Cooling Technologies Enable Hypersonic Systems(from UTRC)
0
40
80
120
160
0 2 4 6 8 10
Mach Number
FlightDuration
-minutes
Accessto Space
Long-Range Strike(e,g, Falcon)
HighSpeedMissile
TBCCDemo
X-51ScramjetDemo
ExistingTechnologies
New TechnologiesRequired
cok
etolerancerequir
ement
0
-
fuel heat sink requirement
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14/2714Next Generation Endothermic Fuels Technology
Endothermic Fuel Cooling Challenges (from UTRC)
Fuel Exit Temperature
HeatSink,B
TU/lbm
TwallMaterialLimit
Wall Heat LoadDH = Qwall / Wfuel
Fuelin Fuel
Exit
Heat in fromcombustor
Section of Combustor Wall HEX
Fuel
Coke Deposit Heat
Heat Exchanger Wall
Fuel
Cooling Channel in HEX
Increase Coking Limit(~2 hr. run duration)
Initiate CrackingEarlier & IncreaseEndotherm
TfuelLimit
Endothermic Technology Goals:
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Cyclohexane Dehydrogenation:Cluster Size Affects Selectivity
Benzene is predominant product.Cyclohexene is predominant product.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
225oC
Pt MWNT
L
TOR(molecules/Ptato
m/s
C6H
12
C6H6
C6H
10
H2
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.70.8
0.9
1.0
225
o
C
Pt MWNT HNO3
hT
I L
H2
C6H
10
C6H
6
C6H
12
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.70.8
0.9
1.0
225
o
C
Pt MWNT HNO3
hT
I L
H2
C6H
10
C6H
6
C6H
12
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.70.8
0.9
1.0
225
o
C
Pt MWNT HNO3
hT
I L
H2
C6H
10
C6H
6
C6H
12
0.0
0.1
0.2
0.3
0.4
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0.70.8
0.9
1.0
225
o
C
Pt MWNT HNO3
hT
I L
H2
C6H
10
C6H
6
C6H
12
Large Pt Clusters ( 2.15 nm) Small Pt Clusters ( 1.32 nm)Untreated MWNT HNO3Treated MWT, Annealed
Synthesis: Lisa Pfefferle, Gary Haller et al(Yale)GISAXS expts shows particles dont change or sinter
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Si D d Bi di E i
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Size-Dependent Binding EnergiesCan Have a Big Impact on Catalysis
Volcanoplot
DecompositionHCO2H (formic acid)
M CO2H
Pt55
Pt201
1.32 nm
2.15 nm
Sh D d t P d t
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Shape-Dependent ProductFormation over (Au)-FeOx
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RG
ASignal(a.u.)
Time (s)
300
250
200
150
100
50
300
250
200
150
10050
Temperature(C
)
500 1000 1500 2000 2500 500 1000 1500 2000 2500
CO2
Pretreatment: 30 min. in 10% H2/He
4%O2/3840 ppm Cyclohexane/He,
70 mL/min., 0.043 g.s/mL
Cyclohexane dehydrogenation
Enhanced benzene productionfor octahedra vs cubes
Higher benzene selectivity forgold-containing catalysts
Good nanoparticle stability andstrong Au-O-Fe interactionseem to favor cyclohexanedehydrogenation over oxidation
78 amu
78 amu
44 amu
44 amu CO2
Fe3O4
Au-Fe3O4
1
0
1
0
Temp
erature(C)
RGASignal(a.u.)
Temperature Programmed Surface Reaction
Octahedra
Cubes
Octahedra
Cubes
M.B. Boucher, S. Goergen, N. Yi and M. Flytzani-Stephanopoulos, Phys. Chem. Chem. Phys.
C t l ti E h t f I iti
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Catalytic Enhancement of Ignitionof Combustion
Pd-based multi-centered nano-ignitors via catalytic heat release
Ignition of methane enhanced by in situgenerated Pd nanoparticlesShimizu et al. Combustion and Flame, 2010. (gas/surface model)Van Devener et al. Journal of Physical Chemistry C, 2009
Pd particles act as multi-centered nano-scale ignitors via catalytic heat release. Smaller particle size (1-5 nm) weakened Pd-O bond strengths; Lower O2
desorption energy .
Use support (TiO2, Al2O3 nps, etc.), other metals, to tune electron densityWang, USC (MURI)
T t C t ll d S l ti it
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Temperature-Controlled Selectivityin Catalytic Reactions of Methane
B
Landman, Ga Tech, Bernhardt, Ulm
Ang. Chem. Intl Ed, 2010J. Phys. Chem. C., 2011
T t C t ll d S l ti it
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High T LowT
Methane combustionEthylene production
T- selectivity
Temperature-Controlled Selectivityin Catalytic Reactions of Methane
G h G h O id d
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Graphene, Graphene Oxide, andClusters
Graphene sheets oxidize fromthe edges inward
Oxygen clusters at defects sites
Metal clusters can bind atdefect sites; distorts sheet
Fe13
Al13
Selloni, Car, Aksay, Princeton Univ.
Developing Theoretical Tools to
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Developing Theoretical Tools toApply to Catalysis
10
Binding Energy of d10Transition Metals to Alkenes byWave Function Theory and Density Functional Theory,
B. B. Averkiev, Y. Zhao, and Donald G. Truhlar,Journal of Molecular Catalysis A 324, 80-88 (2010).
2010 Nobel Prize for Pd-catalyzedcross couplings
Previous: DFT with existingfunctionals is qualitatively wrong forcoupling of an alkene to a Pt or Pd
center. Accomplishment: Developed new
hybrid functionals (M06) that arequalitatively correct and allow DFT tobe applied to this important Nobel-
Prize-winning class of reactions.
Truhlar, U Minnesota
M t l H d id F ti l I i
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11
600
Ignitionresponds[ms]
Ignitionresponds[ms]
Metal Hydride Functional IonicLiquid Fuels
Remarkable impact of cation structure on reactivity noticed in higher performingmetal hydride-base anions - could be a novel design tool!
So far, all hypergolic ILs are based on known anions
efforts move to design ofunprecedented anions incorporating highly reactive hydrazine functionalities
NN B
HH
H
CN
NN
Me
B
HH
H
CN
IDEA: Novel hydrazino tetrazolate anions SUCCESS: Novel hydrazino tetrazole precursors preparedNN
N
N
NHNH2
H
3
X-ray structureNN
N
N
NHNH2
H
n
NN
N
N
NHNH2
n
High energy density ILs for both electrospray and chemical propulsion- Dual Modepropulsive capabilities being realized (Collaboration: with Yu-Hui Chiu/AFRL/RV)
Stable electrospray emission
Isp ~ 5000 s ( electrospray/ion only mode)
Isp >> Hydrazine (chemical mode)
High Isp for station keeping, rephasing & deorbit
High thrust for rapid responseHawkins, Schneider, AFRL/RZ
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Ionic Liquids Ignition
First kinetics model to successfully describe ignitiondelay times and identify important reactions involvedin IL ignition with WFNA(AFRL/RZ and L. Catoire/thru EOARD)
First ion/pair-ion reactivity studies of vaporizedILs using selected-ion flow tube reactor:
A + + X-B+ A+X-B+
(AFRL/RZ and A. Viggiano/AFRL/RV)
D Identified new thermal decomposition pathways
for imidazolium based ILs reactions maycompete with oxidation (AFRL/RZ and LeoneGroup/UC Berkeley)
EMIM+NTf2- + NH4+
EMIM+
NTf2-
NH4+
HNCO + HNO3
Products
K = RateConstant
K
1/2K
2K
Discovered New Plasma Process:
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Discovered New Plasma Process:e- Catalyzed Mutual Neutralization
A+ + XY- + e- neutrals + e- Phys. Rev Lett. 106, 018302 (Jan. 2011)
Never mentioned in literature
Correlates with IR intensity
Requires new mechanism
involving motion-inducedtransitions
Robust, several Br2- sourcesyield the same result
rate constants vary from 10-19
to 10-17 cm6 s-1
6
5
4
3
2
1
0
2000150010005000
kECMN(x10-18
cm6s-1)
Low Frequency IR Intensity (km mol-1)
Br2-
Cl2-
SF6-
SF5-
SF4-
POCl3-
POCl2-
PSCl2-
PSCl-
COCl2-
Ar+ + XY- + e- neutrals + e-
5
6
7
8
91
2
3
GoodnessofFit
3x10-8 4 5 6 7 8
MN rate constant (cm3s
-1)
w/ ECMNw/o ECMN
Poor fit without ECMN
Impacts all negative ion plasmasreentry
plasma assisted combustion
Viggiano, AFRL/RV
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Summary
Catalysis can have transformational impacts on DoD systems
Catalysis greatly impacts energy storage and utilization
New dimensions in catalysis research are emerging
Knowledge of the molecular mechanism is key in developingand optimizing more efficient catalysts
AFOSR leading the way in applying new tools to understandcatalytic mechanisms
Many new areas of opportunity:
Bio-based fuel production
Atomic scale imaging and control of catalysis