Summary of Ph. D. thesis
Title: Catalyst Design for Upgrading of Biomass-Derived Intermediates to Value-Added Chemicals
Shixiang Feng (Supervisor: Prof. Tetsuya Shishido)
Department of Applied Chemistry for Environment, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University
In this thesis, different biomass-derived intermediates including glycerol and glyceric acid were applied as the feedstock for production of value-added chemicals.
Various supported nanocatalysts were designed and performed for different transformation. Based on experimental and theoretical studies, the general conclusion of this thesis can be summarized as follows:
In the work of chapter 1, an efficient chemical synthesis of DHA under relatively mild conditions (303 K, 1 atm air, no pH adjustment) with competitive yield and selectivity over our designed catalyst was achieved. SBA-15 proved to be a good support candidate owing to its high surface area, high thermal stability and neutral properties. The Bi in the catalyst promoted the activity and selectivity mainly in three ways: 1) to cover step sites of high energy on Pt surface, lower the catalytic activity and prohibit the C-C cleavage to reduce poisonous intermediates production; 2) to chelate with glycerol through primary and secondary -OH making it possible to trigger the oxidation of secondary hydroxyl group; 3) to catalyze the isomerization of GLD to DHA which further increase the yield of DHA. The O2 in the reaction affected the reactivity in the following
aspects: 1) O2 was firstly dissociated on Pt into active O atoms. These active atoms were responsible for consuming the generated H atoms after dehydrogenation; 2) high O2
concentration would change the conversion rate of different intermediates and affect the overall activity as well as the selectivity.
In the work of chapter 2, layered Nb2O5 was successfully synthesized and used for the first time in the one-pot conversion of glycerol to LA. Among the niobium oxides examined, the highest conversion (81%) and selectivity (91%) was achieved over the layered Nb2O5. The high catalytic performance of L-Nb2O5 is most likely because of the large amount of Lewis acid sites and Brønsted acid sites that originate from the deformed orthorhombic structure in the a,b-axis and extra-added layers in the c-axis. Based on the catalytic results, glycerol was first converted to triose (DHA and GLD), which was catalyzed by Pt NPs. After acid-catalyzed dehydration, the formed intermediate PA was catalyzed exclusively by the Lewis acid to produce LA through the 1,2-hydride shift reaction.
In the work of chapter 3, alanine was synthesized from glyceric acid for the first time by our designed catalyst. Anatase TiO2 supported Ru was found to be the most efficiently produce alanine (40.4% alanine yield and 77.4% glyceric acid conversion).
Anatase TiO2 was found to be exclusively effective in the ammania solution. The reaction follows a dehydration-reductive amination pathway, with dehydration as a rate-limiting step which is support- and temperature-dependent.
In the work of chapter 4, Pt/WO3/ZrO2 catalysts show specific catalysis for the direct synthesis of 1,5-PeD from THFA. The highest yield of 1,5-PeD was obtained (43%, 15h) on Pt/5WO3/ZrO2. From the characterization of the surface coverage of ZrO2 with the tungsten oxide monolayer, we conclude that W-(OH)-Zr sites at the boundaries
between the tungsten oxide monolayer domain and the zirconia play an important role in the hydrogenolysis of THFA to 1,5-PeD. It is likely that the key to the selective formation of 1,5-PeO is the balance of number of adsorption sites on zirconia and W-(OH)-Zr sites, which promote the formation of primary alkoxide species and secondary carbocation to form 1,5-PeO. The consecutive hydrogenolysis of 1,5-PeD was also catalyzed by Pt/WO3/ZrO2 catalysts to give 1-PeOH.
