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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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    13/2713Next Generation Endothermic Fuels Technology

    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

    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

    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

    18

    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