Atomic level control of catalyst structure for clean fuel ... · Atomic Level Control of Catalyst...
Transcript of Atomic level control of catalyst structure for clean fuel ... · Atomic Level Control of Catalyst...
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Atomic Level Control of Catalyst Structure for Clean Fuel Production
Nuoya Yang Bent research group, Department of Chemical Engineering
GCEP symposium 11/2 ~ 11/3/2016
Bent Research Group
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Syngas conversion – convert carbon in waste to valuable chemical
Bent Research Group
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Atomic Layer Deposition (ALD)-- controllable modification of catalyst structure and composition
Data shown here are 5 cycles MnO
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MnO improves activity and C2+oxy selectivity
Bent Research Group
Rh/SiO2 Rh/MnO support
MnO/Rh overcoat
Rh-Mn co-IMP
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• MnO support didn’t change Rh size distribution
• co-IMP leads to smaller Rh size
ALD-MnO support maintains Rh nanoparticle size
Rh/MnO/SiO2 Rh-Mn (co-IMP) /SiO2
Rh/SiO2
Diameter (nm) Diameter (nm) Diameter (nm)
Cou
nt
Unpromoted MnO-support Rh-Mn co-IMP
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• XPS: MnO/Rh/SiO2 before and after CO adsorption
Mn/Rh atomic ratio: 1.95 before CO 1.15 after CO
• MnO not stable upon CO adsorption
ALD-MnO overlayer – unstable upon CO adsorption
Rh 3d Mn 3d
Bent Research Group
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Infrared spectra -- CO adsorption on Rh surface
• Rh-MnO interface sites weaken CO bond, increase activity.
• Some stepped/defect sites on Rh nanoparticles may be blocked by MnO during impregnation.
• Blocking stepped sites could decrease methane selectivity.
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DFT – MnO stabilizes key transition state Rh-MnO interface: • MnO stabilizes the transition state for C2+oxy synthesis, improves selectivity.
Transition state
CH2-H* (CH4 selectivity)
H-CH2CO* (C2+oxy selectivity)
Surface Rh(111) MnO*/Rh Rh(111) MnO*/Rh
Free Energy
(eV) 1.18 1.16 1.02 0.78
Bent Research Group DFT calculation by Jong Suk Yoo
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Summary
• By controlling the catalyst structure on atomic level, we identified
that Rh-MnO interface site is responsible for activity and selectivity
enhancement for C2+oxy production.
• MnO overlayer is not as effective, due to the instability upon CO
adsorption
• Similar strategy can be generalized to other heterogeneous catalyst
systems to understand the active sites
• Guide the rational design and enable highly controlled synthesis of
heterogeneous catalysts
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Prof. Stacey Bent Bent group Prof. Jens K. Nørskov Jong Suk Yoo, Julia Schumann, Pallavi Bothra
Acknowledgements
Thanks for your attention!