Procedure to tailor activity of methane combustion catalyst: Relation between Pd/PdO x active sites and methane oxidation activity

Abstract

The paper describes a new way to tune the activity of PdO x /Al 2O 3 catalyst—by adjusting the concentration of the impregnation solvent. The effect of tuning on aging was investigated. Catalysts were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Surface properties of the catalysts were measured by Brunauer–Emmett–Teller (BET), NH 3 desorption (NH 3–TPD), and CO pulse chemisorption methods. The activities in methane combustion were measured under lean burn conditions. Activity of the supported catalyst was successfully optimized by adjusting the concentration of carboxylic acid in the impregnation solution. The results showed that the activity of the catalyst is related to the Pd/PdO x ratio as measured by NH 3–TPD method. The results also indicated that low light-off temperature is obtained when the proper proportion of PdO x is able to transform to metallic Pd during heating. The catalyst reconstruction during aging caused the amount of PdO sites to increase and, thereby, some loss of catalyst activity.