Reaction kinetics measurements and analysis of reaction pathways for conversions of acetic acid, ethanol, and ethyl acetate over silica-supported Pt

Reaction pathways for the catalytic conversions of acetic acid, ethanol and ethyl acetate over Pt were studied by collecting reaction kinetics data over a Pt/SiO2 catalyst at temperatures from ca. 500 to 600 K, by conducting density functional theory (DFT) calculations for various adsorbed species and transition states on Pt(111) slabs, and by carrying out reaction kinetic analyses using a kinetic model based on the results from DFT calculations. An equi-molar mixture of CO and CH4 is made from acetic acid, Equi-molar amounts of CO and CH4 are also made from ethanol. Ethane is produced from ethanol and ethyl acetate. Ethanol and acetaldehyde are produced from ethyl acetate. Under all conditions of this study, acetaldehyde and ethanol are present in the reactor effluent as a quasi-equilibrated mixture. General agreement is achieved between the experimental reaction kinetics results and the predictions of the kinetics model for the rates of formation of various products measured. The values of the parameters estimated from reaction kinetic analyses are in good agreement with estimates provided by DFT calculations (within 20 kJ/mol). It appears that the simplified reaction scheme of the present study qualitatively captures the essential surface chemistry involved in the catalytic conversions of acetic acid, ethanol and ethyl acetate over Pt. This simplified reaction scheme can be used to guide further research into the factors that control catalyst selectivity. Sensitivity analyses were conducted to assess which steps in the reaction scheme exhibit the highest degree of rate control for the catalytic conversions of acetic acid, ethanol, and ethyl acetate over Pt. It appears that the reaction kinetics are controlled by six reactions. Further studies of these transition states may provide insight into how the selectivity for hydrogenation of oxygenated hydrocarbons is affected, for example, by forming metal alloy particles, by changing the geometry of the active sites, and by changing the nature of the active metal component. (C) 2001 Elsevier Science B.V. All rights reserved.