MULTI SCALE SIMULATIONS FOR EFFICIENT MULTI-STEP REACTION CASCADES

Efficient multi-step reaction cascades are vital for the pharmaceutical industry and electrochemical devices. Conventionally, one-pot synthesis has been used to carry out such multi-step reaction cascades, which have poor selectivity and yield due to lack of control over the transport of chemical species and kinetics in the system. Therefore, it is desirable to engineer an integrated catalytic system with highly selective catalysts and efficient transport mechanisms.Nature has developed highly efficient transport mechanisms via strategic architectures that use electrostatic interactions, physical confinement, and swing arm techniques to reduce diffusional losses. Such controlled transport is known as ‘substrate channeling’. These natural mechanisms provide essential clues to design novel catalytic platforms. The physical confinement of an intermediate pathway has the potential for 100% intermediate transport. This provides motivation to study the transport in nanoscale confinement. Maximum intermediate retention with minimum bulk access is a key to obtain maximum channeling efficiency. In this work, we study the effect of nanoscale confinement using continuum modeling and molecular dynamics approaches. Continuum modeling of tunnel structures that have active sites confined within shows that increasing confined distance between active site and bulk improves product yield significantly in a kinetically limited system. Molecular dynamics study of interactions between intermediate and tunnel geometry demonstrates that Knudsen diffusion lowers the effective diffusivity of the intermediate. The orientation of solvent molecules inside the tunnel plays a major role in enhancing Knudsen diffusion inside the tunnel. Finally, to increase the intermediate retention, charged molecules may be introduced at the tunnel ends, and retention is highly sensitive to the polarity of the intermediates. Further, we studied existing integrated catalytic platforms for carbon dioxide reduction reaction (CO2RR) and glycerol oxidation reaction cascades. Microkinetic modeling of CO2RR combined with the density functional theory (DFT) technique demonstrates that CO2RR dominates at lower potential with a high surface coverage of carboxylate, a stable intermediate. Nudged elastic band theory calculations of transition states were used to define the transition state of each step of the reaction. A one-dimensional continuum model study of the glycerol oxidation cascade reveals the sensitivity of convective forces in the system on the intermediate transport. Overall, in this work, various aspects of transport and kinetics of the multi-step reaction cascades were studied computationally. This work acts as a primary guide to design novel integrated catalytic platforms for efficient multi-step reaction cascades