Insights into ethanol decomposition over Pt: A DFT energy decomposition analysis for the reaction mechanism leading to C2H6 and CH4

• The PES for ethanol decomposition over a Pt cluster was determined with DFT.
• A Pt5 cluster can capture the main features of the reaction mechanism.
• LMOEDA energy decomposition analysis was applied to some reaction steps.
• CH weakening and CO strengthening explain most of the studied reaction barriers.
• The results help to understand platinum selectivity.

The search for environmentally correct processes is one of the greatest challenges in current energy research. Hydrogen production trough ethanol reforming emerges as a promising technology. In this work, the mechanism for ethanol decomposition over platinum was investigated by density functional theory (DFT). The various reaction intermediaries and transition states were optimized over a cluster of five Pt atoms at the B3LYP-D3/6-31+G(d,p) level of theory for ethanol with the SBKJC ECP basis set for the metal atoms. This approach showed to be fully consistent with experimental observations. Two routes were considered, one leading to the formation of CH4 and CO and the other leading to C2H6. In agreement with previous calculation and experimental studies, the route forming CH4 and CO is favored. The reaction barriers were investigated by the Localized Molecular Orbital Energy Decomposition Analysis (LMOEDA) method. In general, the reaction steps that involve solely the scission of a OH or CH bond present elevate reaction barriers. Some other steps, however, include a concomitant strengthening of the CO bond as the CH bond elongates. These reaction steps present relatively low reaction barriers. For some other cases, it is the distinct interaction with the metal experienced by the transition state and the ground state that determines the energy barrier. The LMOEDA method proved to be an invaluable tool for the understanding of reaction mechanisms and for the rational design of news catalysts.

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