A Systematic in Situ Infrared Study of the Electrooxidation of C3 Alcohols on Carbon-Supported Pt and Pt-Bi Catalysts

The electrooxidation of C3 alcohols (1-propanol, 2-propanol, 1,2-propanediol, 1,3-propanediol, and glycerol) has been studied in alkaline medium on Pt/C and Pt9Bi1/C catalysts by cyclic voltammetry and in situ FTIR spectroscopy. Both catalysts were synthesized with metal particle sizes below 5 nm and were characterized by TGA, AAS, and XRD. The modification of Pt by 10 at. % of Bi decreases the oxidation onset potentials of C3 alcohols down to ca. 200 mV. In situ FTIR spectroscopy measurements indicated clearly that the presence of Bi also led to avoid the C-C bond cleavage during alcohol electrooxidation reactions and, hence, to favor the formation of value-added C3 compounds. Moreover, with respect to a Pd-based catalyst, Pt9Bi1/C presented much higher electrocatalytic activity at low potentials. Systematic evaluation of the positions and intensity changes of absorption bands as a function of the electrode potential allowed determining reaction pathways of electrooxidation of C3 alcohols. It has been shown not only that the secondary alcohol groups are more reactive than the primary ones but also that in the case of glycerol steric limitations due to the presence of two primary alcohol groups could be responsible of the higher oxidation onset potential. At potentials above 0.6 V, the linear 1-propanol bearing a single primary alcohol group leads to the highest activity due to lower steric hindrance of the surface compared with the other alcohols studied.