Periodic DFT Calculations for the Investigation of Carbon-Carbon Bond Cleavage Reactions of Ethene, Ethenol, Propene, and Propenol Over Rh(211) Stepped Versus Rh(111) Planar Lattice Structures

Bethany Therese Cook

Abstract


As the need for fossil fuels increase, there is greater urgency for a more sustainable fuel source to generate energy.  Fuel cells use oxygen and hydrogens gas as fuel to form water and electricity at high efficiency.  However, hydrogen gas is not a naturally occurring compound and is typically generated from other hydrogen-containing molecules such as hydrocarbons.  Plant-derived alcohols and carbohydrates have the potential to be a more sustainable hydrogen source via C-C, C-H and O-H bond cleavage reactions facilitated by a metal catalyst, typically as nanoparticles containing flat planes, stepped edges, and other defects in the surface structure. A fundamental understanding of catalytic reaction mechanisms at these different surfaces are needed for optimal catalyst design and periodic density functional theory (PDFT) calculations can be used to investigate energetic, structural, and electronic effects for elementary steps of the reaction mechanism over extended catalyst surfaces. In this research, C=C double bond cleavage reactions in alkenes and alkenols as a function of chain length were investigated by PDFT on a stepped (211) rhodium catalyst surface, and compared to previous results on a planar (111) surface1. It was found that the reaction energies at the stepped surface are ~14 kJ/mol more favorable for ethene and propene C=C cleavage compared to the planar surface. The reaction energy is similarly more favorable at the stepped surface for alkenols, but is more variable depending on surface-OH interactions. Reaction energetics and the structural dependence of C=C bond cleavage mechanisms for alkenes and alkenols from 2-4 carbon chain lengths will be presented along with insights into the differences between reactions at stepped and planar catalyst surfaces.


Keywords


Alcohols, PDFT, Reaction Energies

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