Solvation of furfural at metal-water interfaces: Implications for aqueous phase hydrogenation reactions.

Metal-water interfaces are central to understanding aqueous-phase heterogeneous catalytic processes. However, the explicit modeling of the interface is still challenging as it necessitates extensive sampling of the interfaces' degrees of freedom. Herein, we use ab initio molecular dynamics (AIMD) simulations to study the adsorption of furfural, a platform biomass chemical on several catalytically relevant metal-water interfaces (Pt, Rh, Pd, Cu, and Au) at low coverages. We find that furfural adsorption is destabilized on all the metal-water interfaces compared to the metal-gas interfaces considered in this work. This destabilization is a result of the energetic penalty associated with the displacement of water molecules near the surface upon adsorption of furfural, further evidenced by a linear correlation between solvation energy and the change in surface water coverage. To predict solvation energies without the need for computationally expensive AIMD simulations, we demonstrate OH binding energy as a good descriptor to estimate the solvation energies of furfural. Using microkinetic modeling, we further explain the origin of the activity for furfural hydrogenation on intrinsically strong-binding metals under aqueous conditions, i.e., the endothermic solvation energies for furfural adsorption prevent surface poisoning. Our work sheds light on the development of active aqueous-phase catalytic systems via rationally tuning the solvation energies of reaction intermediates.

How Buffers Resist Electrochemical Reaction-Induced pH Shift under a Rotating Disk Electrode Configuration.

In mild acidic or alkaline solutions with limited buffer capacity, the pH at the electrode/electrolyte interface (pHs) may change significantly when the supply of H+ (or OH-) is slower than its consumption or production by the electrode reaction. Buffer pairs are usually applied to resist the change of pHs during the electrochemical reaction. In this work, by taking H2X ⇄ 2H+ + X + 2e- under a rotating disk electrode configuration as a model reaction, numerical simulations are carried out to figure out how pHs changes with the reaction rate in solutions of different bulk pHs (pHb in the range from 0 to 14) and in the presence of buffer pairs with different pKa values and concentrations. The quantitative relation of pHs, pHb, pKa, and concentration of buffer pairs as well as of the reaction current density is established. Diagrams of pHs and ΔpH (ΔpH = pHs - pHb) as a function of pHb and the reaction current density as well as of the jmax-pHb plots are provided, where jmax is defined as the maximum allowable current density within the acceptable tolerance of deviation of pHs from that of pHb (e.g., ΔpH < 0.2). The j-pHs diagrams allow one to estimate the pHs and ΔpH without direct measurement. The jmax-pHb plots may serve as a guideline for choosing buffer pairs with appropriate pKa and concentration to mitigate the pHs shift induced by electrode reactions.