Transcript DFT study of Iridium nanocatalysis, R. Kato, et al, SOURCE, 2016

Computational modeling of the dehydrogenation of ethane catalyzed by iridium nanoclusters
*
Ge
Russell Kato, Hao Jiang, Prasuna Gummagatta, Yingbin
Department of Chemistry, Central Washington University, Ellensburg, WA 98926
Rate-Limiting Step
Introduction
Conclusions & Future Work
Ir8 + C2H6 → H−Ir8−CH2CH3
• Alkenes such as ethene and propene are used in our everyday lives
making things from water bottles to furniture.
• Iridium nanoclusters may significantly lower the energy barrier of
ethane/propane to ethene/propene conversion.
M=13
M=15
M=multiplicity
160
140
120
100
80
60
40
20
0
-20
-40
-60
Energy (kJ/mol)
• Petroleum industry uses vanadium oxide catalysts to lower the
energy barrier of alkane-to-alkene conversion to ~100 kJ/mol.
M=11
• Cubic structures of iridium nanoclusters exhibit thermal stability
(Davis et al., Chen et al.) and strong catalytic ability in an oxygen-a
and water-rich chemical environment.
• Catalytic ability: Ir18 > Ir12 > Ir8
• Catalytic ability: corner atom > edge atom > face-centered atom
• The ultimate goal is to design surface-supported long-life
nanocatalysts that convert alkanes to alkenes at low temperatures.
Ethane + ½ O2
Ir8+C2H6
Ir8···C2H6
TS
M=5
M=7
M=9
M=multiplicity
Energy (kJ/mol)
40
Ir12
Ir18
Ir18
M=11
60
0
-20
-40
-60
References
-100
-120
Ir12+C2H6
40
TS
H-Ir12-C2H5
M=3
M=5
• Chen M, Dixon DA (2013) Low-Lying Electronic States of Irn Clusters with n=2-8
Predicted at the DFT, CASSCF, and CCSD(T) Levels. J Phys Chem A 117:3676.
M=7
20
0
-20
Acknowledgments
-40
-60
• Y. Ge thanks CWU Faculty Research Program and School of Graduate Studies and
Research for their financial support.
-80
Ionization energy & electron affinity of Ir
Ionization energy & bond enthalpy of IrO
100
Energy Barrier (kJ/mol)
Mean Absolute Error (kJ/mol)
Ir18+C2H6
80
60
40
20
0
B3LYP
PBE
B98
B971
wB97xd
• Davis JBA, Shayeghi A, Horswell SL, Johnston RL (2015) The Birmingham parallel
genetic algorithm and its application to the direct DFT global optimisation of IrN
(N = 10-20) clusters. Nanoscale 7:14032.
M=multiplicity
Energy (kJ/mol)
• Basis sets (sets of mathematical functions to describe electrons):
• Smaller double-ζ basis sets for optimization and frequency
calculations
• Larger triple-ζ basis sets for single-point energy calculations
• Relativistic effect included in the pseudo-potential for the core
electrons of iridium atoms
Ir12···C2H6
Ir18 + C2H6 → H−Ir18−CH2CH3
• Density functional theory (DFT) methods are used to study iridium
nanocatalysis.
• The B3LYP DFT method accurately models both iridium compounds
and organic chemicals.
Anchoring surface
20
-80
Computational Methods
Ethene + H2O
H-Ir8-C2H5
Ir12 + C2H6 → H−Ir12−CH2CH3
Ir8
• The catalytic ability of an iridium cluster strongly depends on the size
of the cluster and the site where the catalysis occurs.
80
Ir8
Ir18···C2H6
TS
H-Ir18-C2H5
Energy Barrier
• The authors thank CWU Chemistry Department for their support.
71
64.5
60
Ir12
40
21.9
47.8
28.4
Ir18
20
2.6
0
Corner
Corner
Edge
Corner
• Y. Ge thanks CWU Information Services for granting access to their highperformance computers and thanks Bill Glessner for his technical assistance.
Edge
FaceCentered