New Efficient Copper-based Catalytic Systems For Reductive Transformation Of Bio-derived Platform Molecules

The utilization of biomass provides an attractive way to meet the challenges concerned with the continued depletion of fossil reserves as well as the continued increase in chemical and energy demand. As the supply of reliableenergyresources still comes from traditional fossil fules in the near future, the catalytic conversion of biomass to basic and bulk chemicals has become the research focus in recent years. Nowadays, one of the most important ways to achieve the high-value utilization of biomass is the catalytically selective hydrogenation of many well-defined and highly versatilekey platform compounds derived from biomass. While the use of H2 on an industrial scale is expensive and still relies heavily on the fossil resources, minimizing the use of H2 forselective hydrodeoxygenation or reduction with non-noble metal catalystsis of practical and social significance for the development of new generation of environment-friendly biorefining technology based on catalyticreductive transformations.In this thesis, by taking full advantahge of an in situ H2 production via catalytic decomposition of formic acid (FA) or methanol aqueous-phase reforming, we have initiated a systematic study focusing on the development ofnew H2-minimized reductive transformation of a range of bio-derived plafrorm molecules including levulinic acid (LA) and its esterderivatives as well as glycerol. Since H2essentially comes frombio-derived FAor methanol, suchtype of process cannot only fufil the demand for H2 utilization inbiofinerythus circumventing the problems associated with H2 production, storage and transportation, but also offers the possibility for development of new practical and efficient catalytic systems based on on selective reduction reaction.The detailed results for the present thesis are shown below.An extensive screening of potential non-noble heterogeneous catalysts including Fe, Co, Ni and Cu led to the discovery that the Cu/ZrO2catalyst prepared via oxalate-gel co-precipitation (OG) can deliver efficient and selective decomposition of FA. Although the catalytic efficiency of Cu is far lower than the previously reported Au system, the use of earth abundant copper may be justified on its cost and availability. The structure-activity correlation of the catalyst showed that the strong interaction between Cu and ZrO2 is also the key factor affecting their reactivity besides a larger Cu surface area of Cu/ZrO2-OG. The Cu/ZrO2 calcinated at 500℃ performed the best stability compared to the catalysts calcinated at other temperatures, which was due to a large Cu dispersion and tetragonal and monoclinic crystal structure of ZrO2.The study on catalytic hydrogenation reaction of levulinic acid showed that the bio-based LA can be quantatively reduced to γ-valerolactone (GVL) on Cu/ZrO2with the equivalent FA as the sole hydrogen source. The catalytic system has not only the stable performance but also can be applied in the high-yield and economic production of GVL with LA/FA streams directly derived from the true biomass feedstocks like giant reed. The careful study on kinetic data indicated the efficient decomposition of FA and the subsequent LA hydrogenation reactions are both the kinetically key steps to achieve the above-mentioned process. In contrast to the previously reported Au/ZrO2 catalytic system, the realization of Cu catalyzed process, which eliminates the dependence on fossil-fuel H2, has important implications on the design and creation of the novel system based on selective reduction reaction without the dependence on fossil-H2.A further study on the glycerol hydrogenolysis reaction showed that equimolar amounts of FA and glycerol can be converted to high-yield (94%) of 1,2-propanediol (1,2-PDO) using bio-based formic acid as hydrogen source over Cu/ZrO2-OG catalyst in the milder condition than that reported bythe relevant literature. A synergy effect of highly dispersed copper and amphoteric ZrO2 is equally crucial for the reaction, while 20 wt% of Cu content on ZrO2 is identified as an optimum Cu content. The relevant literatures indicatedthat FA involved in the reaction only as a simple hydrogen transfer reagent. Our relevant data kinetically demonstratedthe Cu-catalyzed reaction proceeded via the initial FA decompositionto h2and the subsequent glycerol hydrogenolyssis.Studies on the reductionof methyl levulinate (ML) to GVL using methanol showed that reactivity and selectivity of the ternary metal catalyst Cu/ZnO-Al2O3 is significantly higher than other binary metal catalysts; OG method is superior to the sodium precipitation method.Methanol and water as the solvent could facilitate significantly the improvement on the activity of the hydrogenation reaction and the selectivity to GVL. Based on the kinetics studies, a mechanism involving a facile reduction of ML to GVL viathe in situ H2 generated by methanol aqueous reforming reaction has been proposed. The low-temperature reduction properties of the catalyst and its activity in ML reduction was controlled and optimized through the synergistic interaction of Zn and Al. The role of added water was to improve the reforming activity by inhibiting the generation of the polymerization by-products. The catalyst could be used many times. The structure-activity relation indicated that the small particle size of Cu was crucial.Finally, studies on catalytic conversion of cellulose (the most abundant biomass resource in nature)using FA, methanol or syngas as hydrogen source showed that it is difficult to convert cellulosedirectly over Cu/ZrO2. Nevertheless, it wasserendipitouslydiscovered that, under hydrogenative conditions of of 180℃, 4MPa H2, sorbitol can be obtained inexcellent yield up to ca.90%. Suchhigh yield is far higher than the resultsreportedby the relevant literatures. Subsequent study using H2WO4-Cu/ZrO2as the dual-function catalyst revlead thatdirect hrdrogenolysisof cellulose to ethylene glycol (EG) and 1,2-PDO can be readily achieved, wherein 4 main products were observed with the total yield of EG and 1,2-PDO up to 90%. Theoptimized reaction conditions for celluloseconversion were:3.3 mg/mL,200℃, 4 MPa H2,5 h.