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FROM EXPLORATION TO RATIONAL DESIGN OF SELECTIVE PROPANE DEHYDROGENATION CATALYSTS
Title
FROM EXPLORATION TO RATIONAL DESIGN OF SELECTIVE PROPANE DEHYDROGENATION CATALYSTS
Creator
Hu, Bo
Date
2015, 2015-12
Description
Light olefins, e.g., ethene and propene, are important building blocks of chemical industry for the production of fuels, polymers, lubricants...
Show moreLight olefins, e.g., ethene and propene, are important building blocks of chemical industry for the production of fuels, polymers, lubricants and other fine chemicals. Due to the rapidly increasing production of shale gas, conversion of small alkanes in the shale gas, e.g., ethane and propane, to their corresponding olefins via alkane dehydrogenation could be an important industrial process. This thesis has focused on exploring the novel single site heterogeneous catalysts for selective alkane dehydrogenation and investigating the general principles of rational catalyst design to achieve a better performing (e.g., more active, more stable, highly selective) dehydrogenation catalyst. Based on the observed reactivity of ZnO for olefin hydrogenation and activity of Zn-ZSM-5 catalysts for alkane activation, catalytic properties of isolated Zn2+ were first explored for propane dehydrogenation. The 3-coordinate Zn in single site Zn/SiO2 catalyst was demonstrated to be the catalytically active species that was highly selective for the generation of propene by propane dehydrogenation. DFT calculations revealed that slow β-hydride elimination of alkyl intermediates limited the overall activity of single site Zn/SiO2 catalyst. Thus, single site Co/SiO2 was also prepared in order to take the advantage of fast β-hydride elimination. The higher activity of single site Co/SiO2 emphasized the potential of transition metals for alkane dehydrogenation, and propane dehydrogenation reactivity of transition metals was further explored by investigating single site Fe/SiO2 catalyst. By comparing with metallic Fe nanoparticles and bulk phase Fe oxides catalysts, the 3-coordinate single site Fe2+ was also suggested to be the catalytically active species for selective propane dehydrogenation. However, the catalytic activity of single site Fe/SiO2 catalyst was lower than that of Zn/SiO2. Such result suggested heterolytic cleavage of C-H bonds was slow for transition metals, e.g., Co and Fe, due to their weak Lewis acidity, and it may mitigate the advantages gained in rapid β-hydride elimination. An exploration of ligand effects for improving heterolytic cleavage over single site heterogeneous catalysts was performed. The strength of metal oxygen bond governed by ligand electron donating effects and ligand basicity were found to be the critical chemical descriptors for a facile heterolytic cleavage. Those observed principles of ligand effects would lead to a new strategy of rational catalyst design for a superior dehydrogenation catalyst.
Ph.D. in Chemistry, December 2015
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In situ EXAFS studies of novel Palladium-based anode catalysts for direct ethanol and formic acid fuel cells
Title
In situ EXAFS studies of novel Palladium-based anode catalysts for direct ethanol and formic acid fuel cells
Creator
Su, Ning
Date
2024
Description
In this work we made nanoscale uniform deposition of Pd based anode catalyst on the transition metal Au (with atomic ratio Pd:Au=1:10) support...
Show moreIn this work we made nanoscale uniform deposition of Pd based anode catalyst on the transition metal Au (with atomic ratio Pd:Au=1:10) support of direct liquid ethanol fuel cells (DLEFCs) and direct liquid formic acid fuel cells (DLFAFCs). Synthesizing with uniform dispersion and catalyst nanoparticle dimensions understand the role of Pd reaction on its support in the direct EOR (ethanol oxidation reaction) and FOR (formic acid reaction) pathways, we performed in situ Pd K-edge X-ray absorption spectroscopy measurements as a function of potential using a custom-designed flow cell with the catalyst deposited on the glassy carbon window. We did in-situ EXAFS to better understand the reaction mechanism of Pd1@Au10 anode catalyst with EOR and AOR in nanoscale. Compared EOR with FOR electrochemical performance showed Pd@Au&C played better in ethanol than HCOOH and more stable which the the current density can reach up to 1216.25 mA·mg-1 Pd of EOR with Pd1@Au10&C in 1M KOH+1M EtOH (CH3CH2OH) on the ethanol fuel cells (DLEFCs), and 3.56 times higher of the EOR current compared with commercial Pd@C
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In situ EXAFS studies of novel Palladium-based anode catalysts for direct ethanol and formic acid fuel cells
Title
In situ EXAFS studies of novel Palladium-based anode catalysts for direct ethanol and formic acid fuel cells
Creator
Su, Ning
Date
2024
Description
In this work we made nanoscale uniform deposition of Pd based anode catalyst on the transition metal Au (with atomic ratio Pd:Au=1:10) support...
Show moreIn this work we made nanoscale uniform deposition of Pd based anode catalyst on the transition metal Au (with atomic ratio Pd:Au=1:10) support of direct liquid ethanol fuel cells (DLEFCs) and direct liquid formic acid fuel cells (DLFAFCs). Synthesizing with uniform dispersion and catalyst nanoparticle dimensions understand the role of Pd reaction on its support in the direct EOR (ethanol oxidation reaction) and FOR (formic acid reaction) pathways, we performed in situ Pd K-edge X-ray absorption spectroscopy measurements as a function of potential using a custom-designed flow cell with the catalyst deposited on the glassy carbon window. We did in-situ EXAFS to better understand the reaction mechanism of Pd1@Au10 anode catalyst with EOR and AOR in nanoscale. Compared EOR with FOR electrochemical performance showed Pd@Au&C played better in ethanol than HCOOH and more stable which the the current density can reach up to 1216.25 mA·mg-1 Pd of EOR with Pd1@Au10&C in 1M KOH+1M EtOH (CH3CH2OH) on the ethanol fuel cells (DLEFCs), and 3.56 times higher of the EOR current compared with commercial Pd@C
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