Metal Oxide-Doped Pd-Based Catalysts for Enhanced Formaldehyde Oxidation

In this study, a novel strategy to enhance the performance of palladium (Pd)-based catalysts by doping with metal oxides (Mn3O4, MoO3, and SnO) has been developed in order to overcome the limitations of its low activity and high cost in the catalytic oxidation of formaldehyde (HCHO). The novelty of this strategy lies in the fact that by precisely controlling the types and doping ratios of the metal oxides, a significant enhancement of the electrochemical performance and catalytic activity of the Pd-based catalysts was achieved, while the dependence on precious metals was reduced and the cost-effectiveness of the catalysts was improved. The effects of different metal oxide doping on the catalytic performance were systematically investigated by electrochemical characterization and catalytic activity tests. Among the prepared catalysts, Pd-Mn3O4 showed the most excellent performance, with an electrochemically active surface area of 20.6 m2/g and a formaldehyde oxidation reaction (FOR) current density of 3.5 mA/cm2, which were 31.6% and 169.2% higher than pure Pd, respectively. In a 1000 s timed current method stability test, the limiting current density of Pd-Mn3O4 reached 0.48 mA/cm2, which is 4.4 times higher than that of pure Pd. The excellent catalytic performance is attributed to the abundant surface hydroxyl (-OH) groups provided by Mn3O4, which contribute to the oxidation of formaldehyde intermediates, as well as the electronic synergistic effect between Pd and Mn3O4, which is manifested as a 0.4 eV downshift of the Pd 3d binding energy. In addition, the sensor evaluation showed that the Pd-Mn3O4-based formaldehyde sensor exhibited a high sensitivity (1.5 μA/ppm), excellent linearity (R2 = 0.995), minimal long-term degradation (<7% in 30 days), and ~20-fold selectivity for formaldehyde over interfering gases (e.g., ethanol). This study provides a theoretical basis and practical material reference for the development of efficient and low-cost catalysts for formaldehyde oxidation.