Solvation effects are typically considered for condensed phase reactions, in which solvent molecules can influence chemistry through chemical interactions which vary with the size and composition of the reacting solute molecules. Here, I will discuss solvation effects in two high pressure gas-phase reactions: Fischer-Tropsch synthesis (FTS) and C-C hydrogenolysis on metal surfaces. The solvents, in these reactions, are adlayers of strongly adsorbed species (e.g., CO*, H*) which strongly influence and dictate reacting adsorbates (the solute). At high pressures and coverages, the registry of the adlayer and the underlying metal becomes muddled by high adsorbate mobility. Thus, the adlayer becomes "liquid-like" and the concepts of condensed phase solvation, such as H-bonding, van der Waals interactions, and activation volume reappear -- modified by the altered dimensionality of surfaces compared to condensed phase reactions. We then adapt treatments for non-idealities within condensed phase reaction kinetics to describe a non-ideal surface phase in novel kinetic treatments. C-C hydrogenolysis, a well-studied probe reaction, is used here to determine how to count site requirements within a liquid-like adlayer and reveal inaccuracies in commonly used theoretical catalyst models. Improved models are identified and used to explain how FTS reactions can occur at very high CO* pressures, where no vacancies -- required for reaction -- should exist on Ru and Co catalysts. In FTS, the CO* adlayer directs how CO* species are activated, how C-C bonds are formed, and how H2 and H2O influence rate and selectivity -- enabling, in this case, the reaction to occur with desired selectivity.

Different kind of solvent: Effects of high adsorbate coverages on Fischer-Tropsch synthesis and C-C hydrogenolysis

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.