DFT and Experimental Studies of C-C and C-O Bond Cleavage in Ethanol and Ethylene Glycol on Pt Catalysts

摘要

Density functional theory (DFT) studies of ethanol decomposition were conducted on Pt(111) slabs to investigate the structure and energetics of dehydrogenated ethanol species and transition states for cleavage of C-C and C-O bonds. The ketenyl (CHCO) species has the lowest energy transition state for C-C bond scission, and the energy required to form this species (plus adsorbed H-atoms) from gaseous ethanol is 4 kJ/mol. The lowest energy transition state for C-O bond scission is the 1-hydroxyethylidene (CH_3COH) species, and the energy required to form this species from gaseous ethanol is 42 kJ/mol. In contrast, the lowest energy transition state for C-C bond scission in ethane is the adsorbed ethylidene (CH_3CH) species, and the energy required to form this species from gaseous ethane is 125 kJ/mol. Thus cleavage of the C-C bond in adsorbed species derived from ethanol on Pt(111) should be faster than cleavage of the C-O bond, and cleavage of the C-C bond in ethanol should also be faster than cleavage of the C-C bond in ethane over Pt(111). Reaction kinetics studies were conducted for aqueous-phase reforming of ethylene glycol over Pt/SiO_2 at temperatures of 483 and 498 K and at a total pressure of 22 bar. This catalyst exhibited high activity and selectivity for production of H_2, with low rates of alkane production. It appears that catalysts based on Pt may be promising materials for the selective production of hydrogen by aqueous phase reforming of oxygenated hydrocarbons, such as ethylene glycol.