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Distinguished Guest Seminar - Samir H. Mushrif, Nanyang Technological Unive...

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Room G29-30, Clayton campus New Horizons Building, 20 Research Way

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First–principles based catalyst and solvent design for sustainable processing of biomass feedstock

Samir H. Mushrif

School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore. http://www.ntu.edu.sg/home/shmushrif/

ABSTRACT

Second generation lignocellulosic biomass is the biggest renewable source of carbon. It can be used to produce chemicals and fuels, without putting any stress on the nutritional needs of world population. It also has the potential to reduce greenhouse gases, since the CO2 released can be consumed in a relatively shorter time for growing the biomass. However, setting up a “Bio–refinery” is technologically challenging since biomass contains large amounts of oxygen and is a solid material. Solvents and catalysts that can selectively cleave CO/CH bonds, without breaking CC bonds are needed. In this context, I will present the following two contributions from my group, along with a brief discussion of the first-principles based multiscale modeling tools that we implement, in synergy with experiments.

(I) A novel catalyst for the selective oxidation of cellulosic biomass: CuO, in the form of two dimensional nanoleaves, is shown to be a selective oxidation catalyst for the conversion of glucose to gluconic acid. Under-coordinated lattice oxygen atoms in CuO play the critical role of activating the strong formyl CH bond,1 without further breaking down the glucose molecule into smaller fragments due to CC cleavage. The activity of the lattice oxygen is shown to be superior to that of the chemisorbed oxygen on the metal surface. We also reveal that the surface lattice oxygen incorporates itself into glucose, acting as an oxidizing agent. The reduced CuO catalyst regains its structure, morphology, and activity upon ex-situ reoxidation; whereas, using hydrogen peroxide as a co-solvent enables in-situ regeneration of CuO nanoleaves.2

(II) Screening and selection of solvents for biomass processing: Using key biomass reactions like isomerization and dehydration as examples, we show that solvents can play dual role in biomass reactions. A solvent can either preferentially solvate an “active” functional group of a biomass molecule or its derivative and protect it from taking part into the reaction, or it can also directly participate in the reaction.3 I will discuss in detail how solvent dynamics and nonequilibrium solvation can play a major role in altering the energetics of the rate limiting hydride transfer reaction step in the isomerization reaction. Analyses of changes in the electronic structure of the reacting system and in solvent orientation along the reaction pathway suggest that charge transfer within the biomass molecule polarizes the solvent and that hydride shift takes place in a nonequilibrium solvation environment. Orientational relaxation of the solvent, after the hydride transfer, is observed to be a significantly slower process. The free energy barrier of the reaction is a result of non equilibrium solvation and the exergonicity or endergonicity of the hydride transfer step is governed by the polarizability and relaxation dynamics of the solvent.4


References

(1) Varghese et al., Catal. Sci. Tech., 6, 3984-3996, 2016. (2) Amaniampong et al., Angew. Chem. Int. Ed., 54, 8928-8933, 2015. (3) Mushrif et al., Chem. Eng. Sci., 121, 217-235, 2015. (4) Mushrif et al., Phys. Chem. Chem. Phys., 17, 4961-4969, 2015.

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