Quantifying adsorption-diffusion-reaction of biomass-derived molecules at solid-liquid interfaces

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Distributed manufacturing of chemical building blocks from renewable feedstocks as an alternative to non-renewable fossil resources is an important long-term goal in building a sustainable domestic chemical industry. Transformations and separations of functionalized molecules, such as those derived from depolymerization of lignocellulosic biomass, can be accomplished using porous solids that selectively adsorb and convert them under mild conditions (relatively low temperatures). Such processes are usually conducted in the presence of semi-aqueous solvent systems, which themselves exert strong effects on partitioning, dynamics, and reactivity, significantly altering the effectiveness of heterogeneous catalysts in biomass conversion. The proposed research project aims at developing a fundamental understanding of molecular behavior at solid/liquid interfaces, which is essential for the rational development of durable heterogeneous catalysts and benign solvent systems for processing renewable feedstocks. The project focuses on understanding the nature of the co-adsorption of solvent and solvent molecules in selected microporous and mesoporous materials, in order to generate fundamental knowledge about the role of adsorption in controlling rates and directing selectivity. The objective is to describe and quantify the extent of molecular partitioning at solid-liquid interfaces in conjunction with pore confinement; explore the origins of selective adsorption and consequences for mobility of adsorbed molecules; and combine this information to create new insight into solvent effects in catalytic reactions involving selected oxygenated organic compounds. Thermodynamic measurements of enthalpies of adsorption/absorption in porous materials will be obtained from conventional adsorption equilibrium measurements in combination with isothermal titration calorimetry. The molecular nature of the interactions will be probed using both ex-situ and in-situ solid state Nuclear Magnetic Resonance (NMR) to distinguish between adsorbed/absorbed and free molecules, and to measure their relative proportions and rates of exchange. Density Functional Theory (DFT) and Molecular Dynamics (MD) simulations will be employed to interpret trends in partitioning and adsorption. Reaction kinetics will be recorded in situ and linked to interfacial composition and dynamic behavior. The effect of catalyst pore size and framework topology, hydrophilicity/hydrophobicity, the presence, identity, and density of extra-framework cations, will be explored. A graduate student researcher will be trained in the characterization of solid-liquid interfaces and will learn to make connections between thermodynamic and kinetic measurements. Undergraduate students from under-represented groups will receive mentoring and participate directly in the research. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.