(52b) Elucidating Kinetics of Propane Activation on Pt-Based Electrocatalysts at Room Temperature in Aqueous Acidic Electrolyte.

The surge in shale gas production has boosted the availability of lighter alkanes as feedstocks for chemical manufacturing, driving significant investment in direct conversion technologies—such as electrocatalysis—to satisfy the growing demand for high-value chemicals like alkenes and alcohols. Our recent work has shed light on the mechanism for electrocatalytic activation of propane on Pt electrodes.¹ We demonstrated that, under room-temperature aqueous acidic conditions, propane adsorption is favored at potentials devoid of water-derived adsorbate species. Additionally, via the use of on-line electrochemical mass spectrometry (ECMS), we determined the identity of propane-derived adsorbates as deeply dehydrogenated hydrocarbons with an intact C₃ backbone (C₃H_(8-y)). Despite these mechanistic insights, significant challenges remain in unraveling propane activation kinetics and the factors governing selectivity and conversion to desired products.

In this work, we extend our analysis to uncover propane adsorption and desorption kinetics on Pt. Kinetic analysis using coulometry was used to determine the dependence of adsorption rate on propane partial pressure and active site concentration, revealing reaction orders of 1 and 2, respectively. These findings enabled us to derive kinetic parameters and develop a microkinetic adsorption model consistent with the following scheme: an initial C—H activation step forming propane-derived adsorbate species, followed by the oxidation of H* adatoms to H⁺ ions. These kinetic parameters, consequently, revealed factors influencing adsorption and desorption; for instance, low pH and potentials near potential-of-zero-charge (pzc) for Pt were found to have the highest propane adsorption rates. Furthermore, we developed regression models to deconvolute the m/z signals in the mass spectrometer to determine the identity of desorbed gases. This approach established a methodology for calculating partial currents during in-situ transient experiments in order to elucidate potential-dependent product desorption.

We believe our findings can be directly applied to tune electrocatalysts to study structure-function relationships to selectively valorize alkanes.