Many processes that utilize biomass for production of fuels and chemicals require large amounts of hydrogen to remove oxygen. The research of Dumesic and coworkers identified one renewable route for hydrogen production as aqueous phase reforming of oxygenated hydrocarbons derived from biomass such as sugars and polyols. Recent research in our group and others has centered on the use of bimetallic alloys, which have promoted rates over monometallic platinum or palladium catalysts.In this investigation, monometallic Pt on multi-walled carbon nanotubes (MWCNT), and a series of bimetallic PtMe (1:1 atomic ratio) catalysts (where Me = Mo, Mn, Fe, Co, Ni, Cu, Re) were tested in two reaction systems: aqueous phase reforming (APR) of glycerol and gas phase water gas shift (WGS). By using ex-situ and operando x-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM), it was determined that the catalysts which are selective towards hydrogen production during APR are those which form Pt-shell, Me-core structures due to the reduced nature of the secondary metals, which otherwise will form oxidized surface species, which allow C-O scission via a bimetallic hydrogenolysis site or dehydration over an acidic metal hydroxyl. The correlation of APR turnover rates (TOR) to WGS TOR is due to the removal of CO from surface sites. In the case of PtMe/MWCNT-r catalysts with 3d metal promoters, the water dissociation step is likely facilitated by the promoter, and we propose dissociative chemisorption energy of water as a descriptor of the rate promotion. In the case of PtRe, WGS may be promoted by a different reaction step, possibly relating to CO binding energy. This correlation between APR and WGS, along with structural information from TEM and XAS have been used to assess the nature of the active site and possible chemical descriptors for use in future catalyst development.

Activity relationships between aqueous phase reforming and water gas shift

246th National Meeting (2013)

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