thermal and femtosecond laser-induced co2-surface
TRANSCRIPT
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
End of Chapters 1,2,3: Big Question
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)
End of Chapters 1,2,3: Big Question
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
What Have I Achieved, Thus Far? (2013-2018)
General Conclusions and Future Direction
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
What Have I Achieved, Thus Far? (2013-2018)
General Conclusions and Future Direction
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?
General Conclusions and Future Direction
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?
General Conclusions and Future Direction
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