At solid/liquid interfaces, unlike solid/gas interfaces, the molecules in the liquid can be organized such that those in the vicinity of the surface are appreciably different from the bulk. The cybotactic region is defined as the near-surface portion of the liquid, and is a result of thermodynamics, not mass transport rates. Because the area of the exposed support is typically much larger than that of exposed catalyst, the composition and structure of the cybotactic region will be dominated by liquid-surface interactions. We present molecular dynamics calculations that simulate the structure and composition of the cybotactic region near surfaces relevant to the electrochemically activated addition of hydrogen to biofuel feedstocks. The calculations explicitly identify the different roles of entropy and binding energy on the concentration profiles normal to the surfaces. A first example [1] shows how phenol/water mixtures behave on hydrophilic and lipophilic surfaces, and provides a possible explanation as to why a higher phenol hydrogenation conversion is observed [2] on Pd catalysts on hydrophilic surfaces than on lipophilic surfaces. We show how the concentration of phenol in the cybotactic region can be tuned with surface modifications. In a second example [3], we simulate the speciation on a cathodic surface of a complex solvent mixture containing organics, salts, acids, as a function of cathode charge and temperature. The composition of the cybotactic region, and how it can be tuned with surface modifications, may have critical influence on catalytic processes because rates will be affected by the concentrations of reactants in the cybotactic region. While both examples included have been drawn from the upgrading of bio-oil ex pyrolysis, the principles shown are relevant to any application in heterogeneous catalysis with condensed reaction media.

Speciation at solid/liquid interfaces in the thermal or electrochemical hydrogenation of organic compounds

254th National Meeting (2017)

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