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CO and NO‐induced disintegration of Rh, Pd, and Pt nanoparticles on TiO2(110): ab initio thermodynamics study
Bryan R. Goldsmith, Evan. D. Sanderson, Runhai Ouyang, Wei‐Xue Li
University of California, Santa BarbaraDalian Institute of Chemical Physics
Alternative energyPollution control
Increasing catalyst durability and recyclability is important
Disintegration
Nanoparticle disintegration is a common phenomena
Reactants
Temperature
Pressure
Adatom‐complexes
McClure, S. M.; Lundwall, M. J.; Goodman, D. W. Proc. Natl. Acad. Sci. 2011, 108, 931
Nanoparticle disintegration can cause catalyst deactivation
Rh/SiO2
Changes particlesize distribution
Decreases activity!
Disintegration
Most active size
Or, Nanoparticle disintegration can redisperse agglomerated particles
Rh/SiO2
Disintegration
*
*
Area ratio of facet i
Surface energy of facet i
Metal nanoparticles have different exposed facets
meNP
3 γΔE =R
Surface energyof metal particle
What about the effect of reactants?
Average energy of particle per atom
Energetics of supported nanoparticles
Image courtesy of Michael Engel
meγ = γi ii
f
Nanoparticle
Reactant adsorption lowers particlesurface energy
γmeC=
O
Average energy of particle per atom
[ ]( , )i i ii
me f T P
In presence of gases
meNP
3ΔE =R
Change in surface energydue to reactant adsorption
Ouyang, R.; Liu, J.‐X.; Li, W.‐X. J. Am. Chem. Soc. 2013, 135, 1760
( , , )G R T p G G G disintegration adatom-complex reactant nanoparticle
Disintegration can be modeled by the Gibbs Free Energy
Free energy of disintegrationvia adatom complex formation
M
Ouyang, R.; Liu, J.‐X.; Li, W.‐X. J. Am. Chem. Soc. 2013, 135, 1760
0G disintegration
M
00
0
3( , , ) ( , ) xf x B
pG R T p E n T p k TLn TSR p
medisintegration
γ
Formation energy of adatom complex
Standard gas phase chemical potential
Configurational entropy of complexes
Nanoparticle energy
Ouyang, R.; Liu, J.‐X.; Li, W.‐X. J. Am. Chem. Soc. 2013, 135, 1760
0G disintegration
Disintegration can be modeled by the Gibbs Free Energy
Towards controlling nanoparticle disintegration
Disintegration RedispersionMonomersReactant
Particle Support
Between supported Rh, Pd and Pt catalysts, which one is more susceptible to the disintegration?
Among NO and CO, which one is more efficient for catalyst redispersion?
How sensitive do these results depend on the particle size, temperature and pressure?
Density Functional Theorymodeling using VASP
Projector Augmented Wave method RPBE Functional Plane wave kinetic energy cutoff = 400 eV Forces converged to 0.03 eV/Å
Vacuum layer thickness of 15 Å
(4x2) Rutile TiO2(110)
Periodic model
111 111( , ) [ ( , )] ( , )me i i i mei
meT P f T PT P
Rh Pt Pd
CO binding on (111) facet
CO chemical potential (eV)
Redu
ction in
surface en
ergy (e
V/Å2)
Temperature , Pressure , Coverage
Modeling reduction in surface energydue to reactant adsorption
CO and NO bind strongest to Rh metal compared to Pd and Pt metals
111 111( , ) [ ( , )] ( , )me i i i mei
meT P f T PT P
RhPt
Pd
NO binding on (111) facet
NO chemical potential (eV)
Redu
ction in
surface en
ergy (e
V/Å2)
Rh Pt Pd
CO binding on (111) facet
CO chemical potential (eV)
Redu
ction in
surface en
ergy (e
V/Å2)
Temperature , Pressure , Coverage
Effects of chemical potential and particle size on particle energy
NPE
LESS STABLE
MORE
STA
BLE
(111)NP
3 γΔE =
R
NPE
contours
In the presence of CO In the presence of NO
eV
eV
Adatom formation energies are large and endothermic
E E E adatom/support support bulkFormation energy
Formation energy = 2.88 eV 2.01 eV 3.12 eV
PdRh Pt
Reactant binding stabilizes formation of adatoms
Formation energy = 0.75 eV ‐1.35 eV
C O
Rh
Rh(CO)2Rh(CO)
Rh(CO)2 and Rh(NO)2 have more favorableformation energies than Rh(CO) and Rh(NO)
Formation energy = 0.75 eV ‐1.35 eV
‐0.02 eV ‐1.58 eV
C O
Rh
N
Rh(CO)2
Rh(NO)2
Rh(CO)
Rh(NO)
Formation energy
Rh Pd Pt
Metal(CO) 0.75 0.26 0.09Metal(CO)2 ‐1.35 ‐0.54 ‐0.69Metal(NO) ‐0.02 ‐0.05 ‐0.10Metal(NO)2 ‐1.58 ‐0.67 ‐0.68
Energies are in eV.
The interaction of CO and NO with Rh adatomis greater than for Pd and Pt adatoms
Exothermic formation energypromotes particle disintegration
Formation energy
Rh Pd Pt
Metal(CO) 0.75 0.26 0.09Metal(CO)2 ‐1.35 ‐0.54 ‐0.69Metal(NO) ‐0.02 ‐0.05 ‐0.10Metal(NO)2 ‐1.58 ‐0.67 ‐0.68
Energies are in eV.
Rh(CO)2 Rh(NO)2
The interaction of CO and NO with Rh adatomis greater than for Pd and Pt adatoms
Exothermic formation energypromotes particle disintegration
Pd(CO)2 Pt(CO)2 Pt(NO)2
Higher order complexes also preferred gas phase
These complexes not observed in experiments bound to support
May play a role in gas phase ripening
Gas phase metal complexesnot considered in disintegration analysis
diameter = 20 Å
In agreement with experiment,Rh(CO)2 predicted to form but not Rh(CO)
[1] Berkó, A.; Szökő, J.; Solymosi, F. Surf. Sci. 2004, 566, 337
Exp. Detected
300 K, 10‐1 mbar
notdetected
Pd and Pt not predictedto form adatom complexes
Rh(CO)2
In the presence of CO
CO chemical potential (eV)
Gibbs free energyof disintegration (eV)
Rh(NO)2Exp.Suggested
300 K, 10‐1 mbar
Also in agreement with experiment,Rh(NO)2 predicted to form but not Rh(NO)
Pd and Pt not predictedto form adatom complexes
(Under typical conditions)
In the presence of NO
Gibbs free energyof disintegration (eV)
NO chemical potential (eV)
Extreme conditions
diameter = 20 Å
[1] Berkó, A.; Szökő, J.; Solymosi, F. Surf. Sci. 2004, 566, 337
Experimentally[1] Rh(CO)2 , d < 60 ÅComputed Rh(CO)2 , d < 40 Å
[1] Berkó, A.; Szökő, J.; Solymosi, F. Surf. Sci. 2004, 566, 337
Rh/TiO2(110) more responsive to CO and NO‐induced disintegration than Pd or Pt
Diameter of nanoparticle (Å)
Rh(NO)2Rh(CO)2
Pt(NO)
Pt(CO)Pd(NO)
Pd(CO)
NO is a greater promoter thanCO for NP disintegration
Gibbs free energyof disintegration (eV)
Disintegration can be predictedusing ab initio thermodynamics
Include gas phase disintegration, adatom translation, and particle size‐dependent binding energies!
Goldsmith, B. R.; Sanderson, E. D.; Ouyang, R; Li, W. X. , Submitted
Rh(CO)2 / Rh(NO)2
Rh/TiO2(110) most susceptible to CO and NO‐induced disintegration
NO is a more efficient reactant for particle disintegration than CO
Future work
Acknowledgements
Evan D. SandersonDr. Runhai OuyangProf. Wei‐Xue LiProf. Baron Peters
The Peters group The Wei‐Xue Li group
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