Ind. Eng. Chem. Res. 2004, 43, 3105-3112
3105
KINETICS, CATALYSIS, AND REACTION ENGINEERING Kinetics of Aqueous-Phase Reforming of Oxygenated Hydrocarbons: Pt/Al2O3 and Sn-Modified Ni Catalysts John W. Shabaker and James A. Dumesic* Department of Chemical and Biological Engineering, University of Wisconsin, Madison, Wisconsin 53706
Reaction kinetics studies were conducted on the aqueous-phase reforming of ethylene glycol to produce hydrogen at temperatures near 500 K over Pt/Al2O3 and Raney NiSn catalysts. Ethylene glycol reforming proceeds through similar mechanisms over Pt and NiSn catalysts, involving initial dehydrogenation of ethylene glycol, followed by C-C bond cleavage and water-gas shift. The initial dehydrogenation of ethylene glycol appears to be kinetically significant over Pt/Al2O3, whereas the subsequent rate of C-C cleavage appears to be kinetically significant over R-Ni14Sn. The reforming reaction is fractional order in the ethylene glycol concentration, because of the strong adsorption of the oxygenated reactant, and negative order in the system pressure, through product inhibition by adsorption of H2 and/or CO at high pressures. High selectivity for hydrogen production is achieved for gas-phase products over Pt/Al2O3, whereas the addition of Sn is necessary to avoid alkane formation by methanation over Ni-based catalysts. The rate of methane formation increases at high system pressures, suggesting that the R-Ni14Sn catalyst is still vulnerable to methanation at high H2 and CO2 partial pressures. The reforming of ethylene glycol is accompanied by significant production of acetic acid through bifunctional dehydrogenation/isomerization and dehydration/hydrogenation routes over the metal and support. These bifunctional routes can be used to produce long-chain alkanes or partially reduced chemical intermediates by appropriate use of catalyst-support combinations, catalyst modifiers, and process conditions. CO + H2O T H2 + CO2
Introduction We have recently shown that aqueous-phase reforming (APR) can be used for the production of fuels from renewable resources. In particular, the APR process has been shown to convert biomass-derived oxygenated hydrocarbons selectively to hydrogen1-6 or alkanes7 over a variety of heterogeneous catalysts. In addition to utilizing renewable feedstocks, the APR process eliminates the need to vaporize water and the oxygenated hydrocarbon, which allows the use of nonvolatile oxygenated hydrocarbon reactants (such as glucose and xylose), reduces the energy requirements for producing fuels, and leads to low levels of CO (
