Mechanism Determination for the Electrocatalytic Oxidation of 1,2-propanediol Over Gold and Platinum

Open Access
Author:
Miller, Julie Ann
Area of Honors:
Chemical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Michael John Janik, Thesis Supervisor
  • Enrique Daniel Gomez, Honors Advisor
Keywords:
  • catalysis
  • 1
  • 2-propandiol
  • electrocatalytic oxidation
Abstract:
The selective electrocatalytic oxidation of 1,2-propanediol to lactic and pyruvic acid was studied over gold and platinum catalysts. Previous experimental studies have indicated that the feedstock would oxidize to lactic acid at low overpotentials but would not form pyruvic acid until higher overpotentials were reached. The exact mechanism of these reactions is hard to determine experimentally as the surface reaction intermediates cannot be directly measured. This research utilized density functional theory (DFT) to more accurately determine the mechanism of this oxidation. DFT is a modeling method that uses quantum mechanics to compute the relative energies of each intermediate in predicted hypothesized mechanism. By compiling these energies, a favorable pathway from reactants to products can be determined. On both gold and platinum catalysts, the preferred pathway is through first deprotonating (oxidizing) the terminal oxygen, followed by the deprotonation of the terminal carbon to form lactaldehyde before proceeding to lactic acid. At high potential, further oxidation to pyruvic acid is also favorable. Over a gold catalyst, the unstable intermediate between each step are not strongly bound to the catalyst. This leads to high levels of conversion being unfavorable until high potentials are reached. On a platinum catalyst, the intermediates bind more strongly to the surface and thus higher conversion is obtained. It was also observed that deprotonation and oxidation is far more favorable than breaking carbon-carbon bonds, and oxidation becomes more competitive as the potential increases.