Thermal and Femtosecond Laser-Induced CO2-Surface

Thermal and Femtosecond Laser-Induced CO2-Surface Chemistry on Supported Iron-Oxide Based Nanoparticle Surfaces Under

UHV

Anupam Bera

Advisor: Dr. Atanu Bhattacharya 1

1. Meinshausen et al., Nature, 2009, 458, 11582. Arakawa et al., Chem. Rev. 2001, 101, 953–996

Introduction

CO2 Capture by Adsorption at the Room Temperature

The Problem: CO2 greenhouse gas contributes to global warming(~60%)

2

The Solution: Capture CO2

(1) at the room temperature(2) by earth abundant materials

< 2°C ‘safe level’

Thermodynamically Stable

∆Hf = −393.5 kJ/mole

~300 K Capture of CO2 is a challenging task

Solymosi J. Mol. Catal. 1991, 65, 337−358; Suib, New and Future Developments in Catalysis: Activation of Carbon Dioxide. Ed. Elsevier B.V., 2013, 27–47; Lin et al. J. Phys. Chem. C 2012, 116,26322–26334; Kadossov et al. J. Phys. Chem. C 2008, 112, 7390–7400.

A few important facts: CO2 Adsorption (a) Metal surfaces (Rh, Pd, Pt, Fe, Cu, Re) bind CO2 < 100 K

(b) Metal oxide surfaces physisorption on TiO2 surface chemisorprtion (carbonate formation) on CaO surface

3

Introduction

CO2 Capture at the Room Temperature (~300 K)

~300 K Adsorption of CO2

Adsorption on Metal oxide surfaces

4

Introduction

in particular, on surfaces based on earth abundant mineral iron oxide

Earth’s Abundant minerals are preferred to make the process cost-effective

~300 K Capture of CO2 on Iron Oxide Based Surfaces:

Role of Nanocatalysis

5

Introduction

two catalytic reactions

Ultimate Demand:Not Only Capture but also chemical conversion to fuel

2 2 2CO +H CO+H O Reverse water gas shift reaction

2 2 2 2(2 1)H C H + H On nn nCO n Fischer-Tropsch reaction

Iron Oxide Based Nanocatalysts Used

G. S. Parkinson, Iron Oxide Surfaces, Surf. Sci. Rep. 2016, 71, 272–365

6

1. to Explore Thermally Activated CO2-Surface Chemistry on Iron Oxide-Based Nanoparticle Surfaces

2. to Explore Femtosecond Pulse-Induced CO2 Surface Chemistry on Iron Oxide-Based Surfaces

Aim of the Thesis

Use Surface Science-Based Methodologyunder Ultra-High Vacuum Conditions

A. Bera, A Bhattacharya and co-wrokers Surface Science 2018, 669, 145–153

Surface Science Study of Room Temperature CO2 Adsorptionon Iron Oxide Nanoparticle Surfaces

7

Chapter 1

Objectives:

(1) Synthesis of 2D arrays of Iron Oxide Nanoparticles(2) Structural Elucidation of the Particles(3) Exploration of CO2 surface Chemistry

8

Chapter 1

Surface Science Study of Room Temperature CO2 Adsorptionon Iron Oxide Nanoparticle Surfaces

Metal SaltsSpin Coating

Oxygen Plasma

cleaning

Toluene 0.5 wt % (CMC)

Reverse MicellePrecursor Loaded Reverse Micelle

2D arrays of NPs

4000 rpm

Coated On Si-wafer

Poly-2 vinyl pyridinePolystyrene

25 mTorr O2, 20W,1 Min

(PS)34000-b-(P2VP)18000

10

M/L=0.5,0.75

Chapter 1

Preparation of Model Surfaces: Our Approach Micelle Nanolithography

Chapter 1

2D Arrays of Iron Oxide NPs under SEM

After Spin Coating After Plasma Processing After Annealing

50 nm50 nm 50 nm

24±3.2nm 18±2.5nm 14±2.1nm

at 6000C

16 18 20 22 24 26 28 30 320

5

10

15

20

Fre

qu

en

cy

Diameter (nm)12 14 16 18 20 22 24

0

5

10

15

20

Fre

qu

en

cy

Diameter(nm)

8 10 12 14 16 18 200

5

10

15

20

25

30

Fre

quen

cy

Diameter(nm)

Size:

Secondary Electrons, 3KV, Working Distance 4.0 mm

Magnification: 200-300kX , CeNSE, IISc

Sample

Electron BeamSE (nm range)

Detection:

11

12

Chapter 1

2D Arrays of Iron oxide NPs under XPS

After Plasma Processing After Annealing(6000C)

Fe NPs are Fe+3-oxide NPs Fe+3 stable after high temperature annealing (no reduction)

Al Kα=1486.6 eV 350 W

and a flood gun,45° angle, CeNSE, IISc

Sample

X-rayElectronanalyzer

B.E= hν-K.E-ɸsp

+3

1/2Fe 2p

+3

3/2Fe 2p 711.6 eV

725.1 eV

HRTEM can not be performed on any user-elected flat surfaces

NPs supported on (natively oxidized Si(100), TiO2(110)

GIXRD insensitive: very low particle Density (~ 600 particles/μm2)

Grazing angle X-ray diffraction (GIXRD): Suitable for thin film

Techniques:

GIXRD plot

13

Chapter 1

Cu K𝛼 X-ray radiation ( 𝜆 = 1.54 Å)

At low grazing angle (0.5°) to the sample

Characterization of the NP Structure: The Problem

ki

kf 2θ

αi

14

Element specific All elements (except hydrogen)

But Local orders only (maximum 10Å) with 0.01 Å or better resolution

Chapter 1

Characterization of the NP Structure: The Solution

where I<I0

Beer’s law

Occupied levels

1s1/2K

EFermi

Unoccupied levels

Quasi bound state

Ionization threshold (E0)

Continuum

Edge Energy(E0)

[oxidation state]

Pre edgeX-ray absorption near edge structure (XANES)

edge

7050 7100 7150 7200 7250 7300

2.4

3.2

4.0

4.8

5.6

Energy (eV)

K edge of Fe

Pre-edge(0-50 eV)

EXAFS>50 eV

XANES

electronic structure, oxidation state, chemical environment

(EXAFS)Extended X-ray absorption fine structure

@ Indus-2, RRCAT, Indore

(free electron)

0

( )fI

EI

15

Chapter 1

X-ray Absorption Spectroscopy

2.5 GeV Rotating crystals select the particular energy . Energy range (3-25 KeV)

Dynamical Bending crystals to achieve focusssing, to maintain beam offset zero.

Used For focusing the beam vertically collimation of beam

Used For focusing the beam vertically at sample position

2d = 6.2709Å

Instrumentation

http://www.rrcat.gov.in/technology/accel/srul/beamlines/exafsscan.html

Indus-2 Synchrotron Beamline, RRCAT, Indore

16

Chapter 1

0

( )fI

EI

If

EXAFS: An interference effect

Photoelectron waves either constructively or destructively interfere, giving to oscillation in the amplitude

EXAFS in Practice: measurement of oscillation due to neighboring atoms

0

0

( ) ( )( )

( )

E EE

E

6900 7000 7100 7200 7300 7400 75000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Energy (eV)

0 ( )E0 ( )E

0 ( )E : bare atom background

( )E

17

Chapter 1

EXAFS: in k space

Photo-electron described by a spherical wave with wavenumber : k 0

2

2 ( )m E Ek

In k space, EXAFS represented as , it often weighted with or to amplify the signal at high k

( )k2k 3k

0 4 8 12 16 20-6

-4

-2

0

2

4

6

8

Å-2 )

Å-1)

Fourier Transformation (R space)

0 4 8 12 16 20

-0.1

0.0

0.1

0.2

Å-1)

max

min

21( ) ( )

2

k

n i kR

k

R k k e dk

18

Chapter 1

EXAFS Data Fitting

Average bond length,iR

EXAFS Finally Renders:

( )i k Mean-square disorder of neighboring atoms ( )

iN C.N and type of neighboring atoms ( )

using FEFF code and IFEFFIT program to fit with Expt. EXAFS data

2 2

2 2

[Im( ( ) ( )] [Re( ( ) ( )]

[Im( ( )] [Re( ( )]

dat i th i dat i th ifactor

dat i dat i

r r r rR

r r

R factor < 0.02 : goodness of the fitting

19

Chapter 1

X-ray Absorption Near Edge Structure (XANES)

Fe+3 oxidation state after annealing: consistent with XPS

20

What kind of Fe(III)-oxides are they?(α-Fe2O3, γ-Fe2O3, FeO(OH), Fe3O4 )

1st derivative maxima locates the K-edge position

Chapter 1

Characterization of the Iron-oxides NP Structure

NPs on Si(100)

3 4 5 6 7 8

-2

0

2

4

(k

).k2 (

Å-2

)

k(Å-1)

Expt Data

Fit with -Fe

2O

3

0 1 2 3 40

4

8

12

16

Radial Distance (Å)

Expt. Data

Fit with Fe2O

3

(R

)| (

Å-3

)

Rfactor= 0.02

EXAFS analysis

EXAFS fitting confirms the α-Fe2O3 local structure

α-Fe2O3

Path C.N σ2 R(Å) │(R-Rfeff)│(Å)

Fe-O1 3 0.0033 1.83 0.117

Fe-O2 3 0.0022 2.09 0.018

Fe-Fe2 3 0.0029 2.77 0.198

Fe-Fe3 3 0.0078 3.42 0.055

21

Chapter 1

fitting with γ-Fe2O3, FeO(OH) and Fe3O4 structures (Rfactor= 0.077 to 0.54 )

* Not Fitting *

22

EXAFS analysis

Conclusion: NP Structures CloselyResemble the α-Fe2O3 Local Structure

Chapter 1

CO2 Adsorption on TiO2(110)-Supported α-Fe2O3 NPs: Surface Science Study

Base pressure ~5X10-10 Torr (UHV): Maintains atomically

clean surface during the experiment (>2 hours for 1

full atomic layer)

Inside the UHV Chamber

23

Chapter 1

AESTurbo andIon-Pump

Manipulator

GasDoser

CO2 Adsorption on TiO2(110)-Supported α-Fe2O3 NPs: Surface Science Study

Base pressure ~5X10-10 Torr (UHV): maintains atomically

clean surface during the experiment (>2 hours for 1

full atomic layer)

Inside the UHV Chamber

24

Chapter 1

Before Deposition of NPsClean TiO2 (110)

1. Clean TiO2 single crystal (10x10x1 mm3)(removes surface contaminants C, K) Ion Sputtering(1.5 keV Ar+, 40 Min) High Temperature Oxidation(900 K, 10-5 Torr O2)

2. Take Out TiO2(110) - Deposit NPs by Spin Coating3. Place the sample back to UHV system4. Dose CO2 at 300 K surface temperature

Temperature Programmed Desorption (TPD)

K-type Thermocouple

Gas doser

Data Acquisition

25

0 15 30 45 60 75 90 105 120

300

400

500

600

700

800

900

1000

1100

Tem

pera

ture

(K

)Time (s)

Heating Rate= 4.4K/s

CO2 Adsorption on TiO2(110)-Supported α-Fe2O3 NPs

Chapter 1

300 400 500 600 700 800 900

-800

0

800

1600

2400

3200

CO2 TPD from -Fe

2O

3 NPs

Inte

nsi

ty (

Arb

. U

nit)

Temperature (K)300 400 500 600 700 800 900

-500

0

500

1000

1500

2000

2500

3000

3500

In

ten

sity

(A

rb. U

nit)

Temperature (K)

CO2 TPD from TiO

2 (110)

1. CO2 Dosed at 300 K (room temperature) 2. The CO2 intensity from α-Fe2O3 NPs similar to

background from TiO2(110)

26

CO2 TPD from TiO2(110)-Supported α-Fe2O3 NPs

Chapter 1

CO2 NOT Adsorbed on α-Fe2O3 NPs/TiO2(110) at Room Temperature

Yates et al., J. Phys. Chem. B, 2003, 107, 11700

27

CO2 NOT Adsorbed on TiO2(110) at Room Temperature

Chapter 1

Fully oxidized TiO2(110) surface TiO2(110) surface with O-defects

900 K UHV Annealing

Our results consistent with previous observation on TiO2(110) What Happens on α-Fe2O3 NPs?

Room Temperature

28

In contradiction with our results

not a surface science (UHV) study (not atomically clean)

polycrystalline α-Fe2O3 materials: size of 125–250 µm

polyvinyl alcohol (PVA) method used for preparation

(DRIFT): 1290 cm-1 (νas(COO)), 1560 cm-1 (ν(C=O))

Chemisorption occurs only on the O vacant position

as a carbonate species implying a C2V symmetry

Kureti et al., Phys. Chem. Chem. Phys., 2015, 17, 27011--27018

CO2 Adsorption on α-Fe2O3 particles at Room Temperature

Chapter 1

Above Room Temperature

Argument 1: Atomic Cleanliness of the NP surfaces (Carbon Contaminant ?)

Auger Electron Spectra(AES) confirm the NPs are atomically clean,

cleaned under UHV

29

Argument 2: Sensitivity of the Quadrupole Mass Spectrometric Detection

If O-defects responsible for room temperature CO2-adsorption on α-Fe2O3 NPs,O-defect density must be < 107 defects/cm2

No CO2 Adsorbed on α-Fe2O3 particles at Room Temperature: Rationalizing Observation

Chapter 1

Only One Study: CO2 TPD from Fe3O4(001)

No Study on α-Fe2O3 Single Crystal Surface

30

Surface Science Study of CO2 Adsorption Iron Oxide SingleCrystal Surfaces: Literature is of No Help

Chapter 1

Parkinson et al., J. Chem. Phys., 2017, 146, 014701

1. 2D array by reverse micelle nanolithography on Flat Surfaces2. Stable at high temperature (~900 – 1000 K)3. XANES and XPS revealed Fe+3-oxide 4. EXAFS confirmed hematite (α-Fe2O3 ) NPs

50 nm

31

Hematite (α-Fe2O3 ) NPs

Room Temperature CO2 surface Chemistry from α-Fe2O3 NPs

α-Fe2O3 NPs are not active (despite recent report)

(O-defect density must be < 107 defects/cm2)

Chapter 1

Conclusions

32

End of Chapter 1: Big Question

What Chemical Modification of Iron Oxide NPs Necessary for Room Temperature CO2 adsorption?

33

Objectives:(1) Synthesis of 2D arrays of Pd-Iron Oxide Nanoparticles

(2) Structural Elucidation of the Particles(3) Exploration of CO2 surface Chemistry

Chapter 2

Surface Science Study of Room Temperature CO2 Adsorptionon Pd-Iron Oxide Nanoparticle Surfaces

A Bera, S. Banerjee and A. Bhattacharya and Co-workers Journal Physical Chemistry C 2018, 122, 26528-26542.

34

Chapter 2

2D Arrays of Fe-Pd NPs using Micelle Nanolithography

35

After Spin Coating After Plasma Processing After Annealing(600°C)

50 nm50 nm50 nm

26±3.2nm 12±2.1nm 10±2.0nm

2D Arrays of Fe-Pd NPs (0.5+0.5) under SEM

Size:

6 8 10 12 14 16 180

5

10

15

20

Fre

qu

en

cy

Diamater(nm)4 6 8 10 12 14 16 18

0

5

10

15

20

25

Fre

quency

Diameter(nm)20 22 24 26 28 30 32 34

0

5

10

15

20

Fre

quen

cy

Diameter(nm)

Chapter 2

After O2 PlasmaEtch

After Annealing@6000C, N2 atm.

Reduction of the palladium oxides at high temperature

Multicomponent Fe and Pd systems after high temperature annealing: Fe/Pd=0.81 and Fe+3/Pd+2=2.38

Pd0=66%, Pd+2=34%

Pd+2=100%Fe+3=100%

Fe+3=100%

36

Chapter 2

2D Arrays of Fe-Pd NPs (0.5+0.5) NPs under XPS

Fe+3 even after high temperature annealing inside UHV UHV provides the best environment for inert annealing and results in better

reduction of Pd+2 (23% only), Fe/Pd=0.84 and Fe+3/Pd+2=3.65

77% Pd0 and 23% Pd+2

100% Fe+3

38

2D Arrays of Fe-Pd NPs (0.75+0.5) under SEM and XPS

Chapter 2

Pd+2 doped α-Fe2O3 structure 39

Structure of Fe-Pd NPs: XANES and EXAFS

Chapter 2

0 5 10 15 20 25 30 35 40 45 50600

1200

1800

2400

3000

3600

4200

Inte

nsi

ty (

Arb

. U

nit)

Pd0 3d

Pd+23d

Sputering time (s)

0 5 10 15 20 25 30 35 40 45 50

3200

3400

3600

3800

4000

Inte

nsi

ty (

Arb

. U

nit)

Sputering time (s)

Fe 2p

Core shell structure

Collect XPS spectra

Pd+2-doped α-Fe2O3

Metallic Pd

Sputter the Sample

40

Etching Rate ~ 0.04 nm s -1

Further Structure Analysis of Fe-Pd NPs: XPS Depth Profiling

Chapter 2

41

Chapter 2

Steps before performing CO2 surface study on PdFe-oxide (Shell)@Pd(core) under UHV

1. Clean TiO2 single crystal (10x10x1 mm3)(removes surface contaminants C, K) Ion Sputtering(1.5 keV Ar+, 40 Min) High Temperature Oxidation(900 K, 10-5 Torr O2)

2. Take Out TiO2(110) - Deposit NPs by Spin Coating3. Place the sample back to UHV system and cleaning of NPs4. Dose CO2 at 300 K surface temperature

1s1/2

2s1/2

2p3/2

2p1/2

K I

L

I

II

III

E vac

Measure Kinetic Energy

Ejected electron

EKL1L2,3 = Ek-EL1-EL2

High energy electronbeam

Characterization of Fe-Pd NPs by AES Spectra under UHV

Auger Electron Spectroscopy (AES) element specific and Surface sensitive

(escape depth 5-10 nm)(associated core level B.E)

42

Chapter 2

43

Clean TiO2(110) Fe-Pd Loaded Micelle on TiO2(110)

KLLKLLLMM

MNN

KLL

Atomically Clean TiO2(110)

Obtained by Ar+ sputtering

followed by high temperature

annealing (900 K, 10-5 Torr O2)

Characterization of Fe-Pd NPs by AES Spectra

Chapter 2

Fe-Pd loaded micelle,

Note Large CKLL signal

44

272 eV CKLL feature overlaps with a secondary PdMNN feature at 279 eV

Characterization by AES Spectra

Atomically clean Fe-Pd NPs surface

330 272 279 3.6I I a UHV-clean single crystal Pd(100)

330 272 279 3.45 0.45I I Fe-Pd NPs

Ti

O

Pd FeMNN

PdPdMNN

Clean Pd(100)Clean Fe-Pd NPs/TiO2

LMM

Characterization of Fe-Pd NPs by AES Spectra: Cleanliness

Chapter 2

300 400 500 600 700 8000

1000

2000

3000

4000

5000

6000

sat.

0.69sat.

0.35sat.

0.13sat.

CO

2 I

nte

nsity (

Arb

. U

nit)

Temperature (K)

380K

565K

45

Room Temperature CO2 Adsorption on TiO2(110)-Supported PdFe-Oxide(shell)@Pd(core) NPs

Chapter 2

PdFe-oxide (Shell)@Pd(core) Structure Active for Room Temperature CO2

adsorption

300 400 500 600 700 800 900

0

1000

2000

3000

4000

5000

TPD303K

TPD350K

TPD400K

TPD450K

CO

2 Inte

nsity (

Arb

. U

nit)

Temeprature (K)

PdFe-oxide (Shell)@Pd(core) active upto 450K46

CO2 uptake decreases linearly with increasing temperature

Room Temperature CO2 Adsorption on TiO2(110)-Supported PdFe-Oxide(shell)@Pd(core) NPs

Chapter 2

47

Room Temperature CO2 Adsorption on PdFe-Oxide(shell)@Pd(core) NPs: Role of Bimetallization

Chapter 2

Corresponding Single Component NPs NOT

Active

48

Room Temperature CO2 Adsorption on PdFe-Oxide(shell)@Pd(core) NPs: Role of Bimetallization

Chapter 2

87% metallic Pd0 species and 13% oxidized Pd+2 species

TiO2(110)-Supported Pd NPsTiO2(110)-Supported α-Fe2O3 NPs

Destiny of Single Component NPs:Fe+3 remains Fe+3 but Pd+2 reduced to Pd0

Redhead Method: 1 max

max

ln 3.64dE AT

RT

maxT max. peak temperature, 14.4sdTKs

dt

13 1

1 1 10A s

n = 1, Ed = 1.52 eV

300 400 500 600 700 8000

1000

2000

3000

4000

5000

6000

sat.

0.69sat.

0.35sat.

0.13sat.

CO

2 Inte

nsity (

Arb

. U

nit)

Temperature (K)

380K

565Kmax 565T K

max 380T K

n = 1, Ed = 1.01 eV

P.A. Redhead, Vacuum 12 (1963) 203

expnn dEd

dT RT

49

Room Temperature CO2 Adsorption on PdFe-Oxide(shell)@Pd(core) NPs: Activation Energy

Chapter 2

1. 2D array of multicomponent NPs by micelle nanolithography2. Stable at high temperature (~900 – 1000 K)3. XANES and XPS reveals presence of Fe+3, Pd+2 and Pd0

4. EXAFS confirmed Pd doped hematite (Pd-α-Fe2O3 ) NPs

51

Pd+2-doped α-Fe2O3

(shell)@Pd(core) NPs

Room Temperature CO2 Surface Chemistry

Pd+2-doped α-Fe2O3 (shell)@Pd(core) NPs are active,

but not single component NPs, Two Activation Energies:

1.52 and 1.01 eV

Chapter 2

Conclusions

52

End of Chapter 2: Big Questions

(1) Why Pd+2-doped α-Fe2O3 shell Structure Active for Room Temperature CO2 adsorption?

(2) Meaning of Adsorption Energies, 1.52 and 1.01 eV

53

Objectives:(1) Role of O-Defects in CO2 Adsorption

(2) Role of Pd+2-Doping in Creating O-Defects(3) Theoretically Explore CO2 Adsorption Energies and Configurations

Chapter 3

Periodic Density Functional Theory Study: Adsorption of CO2 Model α-

Fe2O3(0001) and Pd+2-doped α-Fe2O3 (0001) surfaces

A Bera, S. Banerjee and A. Bhattacharya and Co-workers, submitted to Journal of Physical Chemistry A (2018)

54

Chapter 3

Computational Surface Science: Periodic Density Functional Theory

Calculations of Model Surfaces

Using Vienna Ab initio Simulation Package (VASP)

PBE functional + generalized gradient approximation + a plane wave basis set with the energy cutoff of 650 eV, PAW pseudopotential, a vacuum region of 20 Å between the slabs.

α-Fe2O3(0001)

CO2 on Pristine α-Fe2O3(0001) Surface: Very Weak Interaction

− 0.23 eV Eads -0.05 eV -0.11 eV55

Chapter 3

Eads -0.71 eV -1.03 eV56

Chapter 3

CO2 on α-Fe2O3(0001) Surface: Moderately Strong Interaction

Pd+2-doped α-Fe2O3(0001)

Two Fe+3 replaced by two Pd+2 ions: Rendering one O Vacancy

∆E=0 eV

57

Chapter 3

∆E=1.15 eV ∆E=0.30 eV

Eads-1.51 eV -1.71 eV -0.78 eV

58

Chapter 3

CO2 on Pd+2-doped α-Fe2O3(0001): Very Strong Interaction

Conclusions

59

Chapter 3

DFT Prediction:CO2 Desorption Energy from Pd+2-doped α-Fe2O3(0001)

In the range 1.5-1.7 eV

TPD Experimental Estimation:CO2 Desorption Energy from Pd+2-doped α-Fe2O3 NPs

~1.5 eV

60

End of Chapters 1,2,3: Big Question

Is There Any Other (Novel) Way to Look at Catalytic Room Temperature Adsorption Problem of CO2

Fundamentally ?

Well-known Way of Looking at Catalysis Problem(blind man seeing an elephant)

Surface

Adsorbates

Activation Energy Perspective:

/~ aE RT

k Ae

Arrhenius Equation (1889)

Strong Binding: HighWeak Binding: Low aE

/aE RTmd Ae

dT

Polanyi-Wigner Equation


CO2 on Pd+2-doped α-Fe2O3

(shell)@Pd(core): 1.52 and 1.01 eV

Surface

Adsorbates

Time-domain Perspective:

Strong Binding: LowWeak Binding: High

Energy Exchange Time-Scale

Strongly bound species exchanges energy faster than

weakly bound species

aECounter-intuitive if consider

Novel (Our) Way of Looking at Catalysis Problem(blind man seeing an elephant)


Chemists have mostly neglected this perspective, thus far.

Understanding Femtochemistry of Nanocatalysis:

An Attempt with TiO2(110)-supported CO2/Pd+2-doped α-

Fe2O3-(shell)@Pd(core) NPs

63

Chapter 4

Schematic Layout of Experimental Set-up

64

Chapter 4

65

1

( , )exp ( ) / 1B

f Tk T

Fermi-Dirac Distribution

Generation of hot electrons: wavelength independent butFluence (energy/cm2) dependent for metals

Two Temperature Model (2TM)

Surface Femtochemistry: Underlying Mechanisms

Understood So Far

Chapter 4

300 400 500 600 700 8000

1000

2000

3000

4000

5000

6000

7000

8000

Post-Irradiation

Pre-Irradiation

CO

2 Y

ield

(A

rb. U

nit)

Temperature (K)

807 nm, 40 fs Pulse Induced Chemistry:Pre- and Post-Radiation CO2 TPDs on FePd Multicomponent NPs

No Change: No Femtosecond Pulse Induced Chemistry

66

Chapter 4

absorbed fluence 3.13 mJ/cm2

Pd(100) Example: Oadsorbed + Oadsorbed = O2,gas

absorbed fluence 2.86 mJ/cm2.

67S. Banerjee, A. Bera, A Bhattacharya, J. Phys. Chem. C 2018, 122( 45) 26039-26046

807 nm, 40 fs Pulse Induced Chemistry:Pre- and Post-Radiation TPDs: Rationalizing Observation

Above Observation Consolidates Our CO2-Hypothesis

Chapter 4

68

Pd+2-Doped α-Fe2O3 (shell)@Pd(core) NPs has a Semiconducting Shell and

Metallic Core

Chapter 4

807 nm, 40 fs Pulse Induced Chemistry:Pre- and Post-Radiation CO2 TPDs: Rationalizing Observation

400 450 500 550 600 6500.0

0.1

0.2

0.3

0.4 -Fe

2O

3 NPs

No

rmaliz

ed A

bsorp

tio

n

wavelength (nm)

PdFe NPs NPs

563 nm

700 725 750 775 800 825 850 875 900

0

1000

2000

3000

4000

5000

centre

=807.6 nm

FWHM=34.5 nm

Spectrum

Fit

Inte

nsity (

Arb

. U

nit)

Wavelength (nm)

807 nm, 40 fs

69

Can CO2 Femtochemistry be initiated with higher fluence (greater

than 3.13 mJ/cm-2) ?

Chapters 4: Big Question

807 nm cannot Excite “Shell”

but can easily excite “Metallic Core (Pd)”

70

Chapter 4

807 nm, 40 fs Pulse with higher Fluence in Pulse counting mode

F= 30 mJ/cm-2

CO2 and CO deosrption yield at various position of the sample by higher fluence

a highly nonlinear fluence dependent desorption yield

71

Conclusions

Chapter 4

1. Femtosecond Pulse-Induced Chemistry of CO2 can be Observed at 807 nm only with higher fluence (greater than

3.13 mJ/cm-2)

2. A highly nonlinear fluence dependence CO2 desorption yield observed

72

What Have I Achieved, Thus Far? (2013-2018)

General Conclusions and Future Direction

1. Obtained General Strategy for Preparation of 2D Arrays of NPsFirst Step to Study Nanocatalysis Fundamentally

2. Obtained General Strategy for Structurally Characterize Single

and Multicomponent NPs:First Step to Find Structure-

Reactivity Correlation

73



3. Found Iron Oxide-Based Surfaces Which are Active for Room

Temperature CO2 Adsorption:First Step to Explore CO2-Surface

Chemical Dynamics

4. Found Microscopic Detailsof Role of Pd+2-Doping in

CO2 Adsorption on α-Fe2O3

First Step to UnderstandMechanism of Femtochemisty

74



5. Finally, found Response of Femtosecond Pulses-Induced CO2-Surface Chemistry at 807 nm with higher Fluence:

First Step to ExploreCO2-Surface Femtochemisty

75

Questions Which are Left Answered and Unaddressed, Thus Far?


Pd+2-Doped α-Fe2O3 (shell)@Pd(core)

400 450 500 550 600 6500.0

0.1

0.2

0.3

0.4 -Fe

2O

3 NPs

No

rmaliz

ed A

bsorp

tio

n

wavelength (nm)

PdFe NPs NPs

563 nm

Future Direction 1: Excited with 563 nm Femtosecond Pulses

2: Exploration of fs 2 pulse correlation spectroscopy to find out the ultrafast desorption dynamics

76

Questions Which are Left Answered and Unaddressed, Thus Far?


2 2 2CO +H CO+H O Reverse water gas shift reaction

2 2 2 2(2 1)H C H + H On nn nCO n Fischer-Tropsch reaction

Pd+2-Doped α-Fe2O3 (shell)@Pd(core) is active for Room Temperature CO2

Adsorption

Future Direction 2: Are they Active For H2 and CO as well ?

77

Department of Inorganic and Physical Chemistry, IISc:

Dr. Atanu Bhattacharya (Advisor)

Sourav Banerjee (Surface Science Experiments)

Dr. Nawirit Karmodak (Prof. Jemmis Group, DFT)

Sankhabrata Chandra (Femtosecond Laser)

Jayanta Ghosh (AIMS, Molpro)

Sampad Bag

Prof. S. Sampath (initial phase synthesis)

Dr. Sai G. Ramesh (IPC Cluster)

CeNSE, IISc

XPS, SEM and AFM

SSCU, IISc

Prof. T. N. Guru Row (GIXRD)

Indus-2 Synchrotron, RRCAT, Indore

Dr. D. Bhattacharyya and S. N. Jha (XAS)

Financial Support

DST Nano Mission, NET-CSIR, GARP

Acknowledgement

7878

Thank You For Your Attention

Thermal and Femtosecond Laser-Induced CO2-Surface Chemistry on Supported Iron-Oxide Based

Nanoparticle Surfaces Under UHV

Documents

Thermal and Femtosecond Laser-Induced CO2-Surface