Different promoting roles of ruthenium for the oxidation of primary and secondary alcohols on PtRu electrocatalysts.

[Display omitted] • The oxidation of secondary alcohols is favored on PtRu compared to Pt. • Ru plays a different role in the oxidation of the secondary and primary alcohols. • The presence of Ru enables the adsorption of an O-bound intermediate. • Secondary alcohols are oxidized through a different pathway on PtRu compared to Pt. • The bifunctional mechanism is limited to the oxidation of primary alcohols. This study shows remarkably different features between the oxidation of secondary and primary C 3 -C 5 alcohols. The oxidation of primary alcohols is controlled by the oxidative removal of blocking adsorbates, such as CO, formed after the dissociative adsorption of alcohol molecules. Conversely, secondary alcohols do not undergo dissociative adsorption and therefore their oxidation is purely controlled by the energetics of the elementary reaction steps. In this respect, a different role of ruthenium is revealed for the electrooxidation of primary and secondary alcohols on bimetallic platinum-ruthenium catalysts. Ruthenium enhances the oxidation of primary alcohols via the established bifunctional mechanism, in which the adsorption of (hydr)oxide species that are necessary to remove the blocking adsorbates is favored. In contrast, the oxidation of secondary alcohols is enhanced by the Ru-assisted stabilization of an O-bound intermediate that is involved in the potential-limiting step. This alternative pathway enables the oxidation of secondary alcohols close to the equilibrium potential. [ABSTRACT FROM AUTHOR]