Glycerol-to-Lactic Acid Conversion on a Pd3Pb Surface via a Faradaic and Non-Faradaic Tandem Catalytic Process

The glycerol oxidation reaction (GOR) over Pd-based catalysts to produce high-value C3 chemicals, especially lactic acid (LA), has attracted considerable research interest. However, the underlying reaction mechanism remains poorly understood, and the distinction between Faradaic and non-Faradaic processes has long been ambiguous. Herein, we fabricated a Pd3Pb alloy model catalyst, which achieves an exceptional C3 selectivity of 87.4% and LA selectivity up to 58.3% at 0.65 V vs RHE in alkaline media, in contrast to ∼20% LA selectivity on Pd. It also delivers a current density of 224 mA cm-2 and retains robust catalytic stability during ten consecutive electrolysis cycles. Combining in situ electrochemical infrared reflection-absorption spectroscopy, quasi-online high-performance liquid chromatography, and density functional theory calculations, we reveal that the downshifted d-band center of Pd in Pd3Pb weakens the surface adsorption of the glyceraldehyde (GLD) intermediate generated via the Faradaic process. Consequently, desorbed GLD diffuses into the electric double layer and converts into LA through non-Faradaic reactions. This work adopts a tandem catalytic strategy involving Faradaic and non-Faradaic processes to switch the major products of GOR from glyceric acid (GLA) to LA, which might offer a new insight and guidance for the valorization of small molecular compounds.