DFT studies for cleavage of C$z.sbnd;C and C$z.sbnd;O bonds in surface species derived from ethanol on Pt(111)

Abstract Results from self-consistent periodic DFT calculations were used to study the relative stabilities and reactivities of surface species on Pt(111) derived by subsequent removal of hydrogen atoms from ethanol. Within each C 2 OH x isomeric set, the lowest energy surface species (with respect to gaseous ethanol and clean Pt(111) slabs) are ethanol, 1-hydroxyethyl (CH 3 CHOH), 1-hydroxyethylidene (CH 3 COH), acetyl (CH 3 CO), ketene (CH 2 CO), ketenyl (CHCO), and CCO species. The energies of these species are −27, −28, −55, −84, −82, −88, and −53 kJ/mol, respectively, where the corresponding H atoms removed from ethanol are adsorbed on separate Pt(111) slabs. Transition states for CC and CO bond cleavage reactions were calculated for the most stable intermediates and for intermediates leading to exothermic bond cleavage reactions. A linear correlation between the energies of transition state and the energies of corresponding surface species was used to estimate transition-state energies of remaining reaction intermediates. The 1-hydroxyethylidene (CH 3 COH) species has the lowest energy transition state (42 kJ/mol) for CO bond cleavage, and the adsorbed ethylidyne (CCH 3 ) and hydroxyl product species lead to a favorable energy change for this CO bond cleavage reaction (−38 kJ/mol). The ketenyl (CHCO) species has the lowest energy transition state (4 kJ/mol) for CC bond cleavage, and the adsorbed CO and methylidyne (CH) product species lead to a very exothermic energy change for this reaction (−144 kJ/mol). Results from DFT calculations, combined with transition state theory, predict that the rate constant for CC bond cleavage in ethanol is faster than for CO bond cleavage on Pt(111) at temperatures higher than about 550 K. In addition, the calculated value of the rate constant for CC bond cleavage in ethanol is predicted to be much higher than for CC bond cleavage in ethane on Pt(111). Similarly, the rate of CO bond cleavage in ethanol is predicted to be much higher than for CO bond cleavage in carbon monoxide on Pt(111).

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