(207a) Supported Bimetallic Catalysts for the Production of γ-Valerolactone

Transportation fuels may be produced from simple carbohydrates in cascade processes which improve upon the energy density of the feedstock and facilitate C-C bond formation to build the molecular weight of the final product.  Such processes generally involve the isolation of intermediate platform chemicals, of which γ-valerolactone (GVL) is a particularly versatile example.  Commonly, GVL is produced by hydrogenation of levulinic acid, over supported metals such as Ru/C.  Once prepared, it may be used directly as a fuel additive or alternatively processed to yield jet fuel components.   To date, the most significant hindrance to large scale demonstration of GVL-centered biorefining is the cost associated with its production, much of which is attributed to recovery and purification of levulinic acid. 

Though they have demonstrated appropriate activity, Ru catalysts commonly used in the reduction of levulinic acid suffer a marked sensitivity to residuals from prior stages (sulfuric acid, for example) and have a limited capacity for processing unrefined solutions of levulinic acid.  Further, supported Ru catalysts are not entirely selective for carbonyl reduction (they readily saturate carbon-carbon double bonds, for example), which requires that levulinic acid undergo extensive refining to remove residuals prior to GVL production.     

In recent research, we have observed that bimetallic catalysts are more robust than traditional monometallic species and may allow relaxed tolerances on levulinic acid purity to facilitate low-cost production of GVL and its many upgrading products.  For example, the addition of certain promoters to Ru, such as Re, confers superior stability and activity in the presence of sulfuric acid, offering the possibility of direct hydrogenation of unrefined levulinic acid solutions.  Other bimetallic systems enhance the selectivity for reduction of the ketone moiety, allowing intensified strategies by which GVL may be produced selectively in the presence of functionalized extracting solvents without intermediate distillation.    

In this session, we shall outline strategies which rely upon the unique capabilities of bimetallic catalysts and may help to establish GVL as a commodity scale platform for fuels production.  In addition, we shall present detailed characterization of various bimetallic systems to describe their improved stability, activity, and selectivity in processing lignocellulose derived solutions of levulinic acid.