Abstract
Butanol is a by-product obtained from biomass that can be valorized through aqueous phase reforming. Rh/ZrO2 catalysts were prepared and characterized, varying the size of the support particles. The results showed a relatively mild effect of internal mass transport on butanol conversion. However, the influence of internal transport limitations on the product distribution was much stronger, promoting consecutive reactions, i.e., dehydrogenation, hydrogenolysis, and reforming of propane and ethane. Hydrogen consuming reactions, i.e., hydrogenolysis, were more strongly enhanced than hydrogen producing reactions due to internal concentration gradients. Large support particles deactivated faster, attributed to high concentrations of butyraldehyde inside the catalyst particles, enhancing deposit formation via aldol condensation reactions. Consequently, also the local butyric acid concentration was high, decreasing the local pH, enhancing Rh leaching. The influence of internal transfer limitation on product distribution and stability is discussed based on a reaction scheme with three main stages, i.e., (1) formation of liquid intermediates via dehydrogenation, (2) formation of gas via decarbonylation/decarboxylation reactions, and (3) hydrocarbon hydrogenolysis/reforming/dehydrogenation.
Highlights
The environmental issues and the depletion of conventional sources of energy demand development of alternative and sustainable technologies
The Rh particle size distribution on spent catalyst was determined by scanning tunneling electron microscopy (STEM) using Jeol 2200FS equipped with spherical aberration corrector
In which r’A is the observed reaction rate, R is the catalyst particle radius (m), ρc is the density of the catalyst, CAs is the concentration of butanol on the external catalyst surface and De is the effective diffusion coefficient (m2 s−1), calculated according to Equation (7): De in which DAB is the binary diffusion coefficient of butanol in water (m2 s−1), φp is the catalyst pellet porosity and τ is the tortuosity factor
Summary
The environmental issues and the depletion of conventional sources of energy demand development of alternative and sustainable technologies. A considerable effort has been put on the production of hydrogen from oxygenated hydrocarbons, e.g., via aqueous phase reforming (APR) (Cortright et al, 2002). The Dumesic research group demonstrated that hydrogen can be produced from alcohols in water in the condensed phase, with a noteworthy energetic advantage compared to the conventional steam reforming as evaporation of water is circumvented (Davda et al, 2005). Among the possible reactants for this process, oxygenates with 1 to 1 O to C ratios are preferred for H2 production, Mass Transfer Effect in APR via reforming and subsequent water gas shift reaction (Cortright et al, 2002; Shabaker et al, 2003a; Davda et al, 2005). Methanol is the most investigated mono-alcohol, thanks to its optimal carbon/oxygen ratio
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