Hydroxyl Promoted Preferential And Total Oxidation Of CO Overε-MnO₂ Catalyst

The trace CO hydrocarbon reforming-obtained hydrogen is toxic to the Pt-electrode of proton exchange membrane fuel cell,which reduces its service lifetime.So it is necessary to remove the undesired CO in excess hydrogen.Moreover,CO is also a major air pollutant and harmful to humans and animals.Catalytic oxidation of CO is one of the most effective ways to eliminate CO in air and hydrogen-rich atmospheres.In this paper,ε-Mn O₂ material（Mn O₂-P）was synthesized by hydrothermal method of citric acid,and a catalyst material（Mn O₂-AT）with abundant surface hydroxyl groups was obtained by simple acid washing.Subsequently,the catalytic performance of Mn O₂-P and Mn O₂-AT catalysts was investigated in total and preferential oxidation of CO.Under the condition of total oxidation of CO,it completely oxidizes CO at 90℃.It also exhibits excellent CO catalytic oxidation,CO₂ selectivity and stability in CO preferential oxidation.The physical properties of the catalyst were characterized by XRD,N₂adsorption-desorption experiments,SEM,TEM,Raman and EXAFS.Subsequently,the chemical and surface properties of the samples are characterized by OSCC,CO-TPR,H₂-TPR and CO-TPD.The FT-IR,TPD and in-situ DRIFTS methods were used to analyze the surface groups of the catalyst in detail and proposed a catalytic mechanism according to the results.Finally,the kinetic parameters of Mn O₂-AT in total and preferential oxidation of CO were test and the effect of hydrogen on the catalytic oxidation of CO was discussed.The acid washing process greatly improves the catalytic performance of the catalyst in total and preferential oxidation of CO.According to the characterization results,acid washing does not destroy the crystal and pore structure ofε-Mn O₂,but the spherical structure of Mn O₂-P is destroyed into fragment morphology.The acid washing simultaneously removes the amorphous layer on the surface of Mn O₂-P,and forming a large number of surface defects on the surface.Moreover,acid washing greatly increases the surface hydroxyl groups,which directly participats in the catalytic oxidation of CO and forms thermally unstable bicarbonate intermediate.The hydroxyl-bicarbonate mechanism is proposed and proved by the kinetic experiments.It is found that H₂ reduces the activation center of O₂ on the surface and its catalytic activity.