Catalytic reactions in condensed phase are important for applications such as biomass conversion and wastewater remediation. As with many heterogeneous catalytic reactions, the adsorption of the reacting species on the catalyst surface plays a significant role in the reaction kinetics, influencing adsorption/desorption rates as well as surface reaction barriers based on stabilization/destabilization of the transition states. Although adsorption energies for gas-phase reactions can be modeled with increasing accuracy by density functional theory or measured directly through the use of vacuum calorimetry, adsorption in the condensed phase is not as well understood. Here we will discuss experimental methods in aqueous-phase to understand how organics adsorb onto platinum group metals in order to extract adsorption free energies, entropies, and enthalpies. The measured values help explain some catalytic behavior observed in aqueous phase, for example how aromatics such as phenol can be hydrogenated at room temperature on metals in aqueous-phase, whereas in gas phase higher temperatures are required because of how strongly phenol is bound to the metal surface. Through these results we identify that a simple bond-additivity approximation of the system, incorporating the displacement of water from the surface and the solvation of the organic molecules, can semi-quantitatively explain the differences between gas-phase calorimetry (or calculations) and aqueous-phase experimental measurements. In particular for water, the adsorption enthalpy of organics is significantly reduced, proportionally to the adhesion energy of the water to the metal. We show that this model explains behavior for aqueous-phase adsorption of furfural, phenol, benzaldehyde, benzyl alcohol and cyclohexanol on both Pt and Rh surfaces. This understanding opens up the opportunity to tune adsorption through the use of solvents, depending on the interaction of the solvent with the solid surface.

Impact of liquid solvents on heats of adsorption: Understanding aqueous-phase hydrogenation on platinum group metals

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

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