The Mechanism Studies of Ethanol Oxidation on PdO Catalysts by TPSR Techniques

Abstract

The paper studies the direct oxidation of ethanol and CO on PdO/Ce_0.75Zr_0.25O₂ and Ce_0.75Zr_0.25O₂ catalysts. Characterization of catalysts is carried out by temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR) techniques to correlate with catalytic properties and the effect of supports on PdO. The simple Ce_0.75Zr_0.25O₂ is in less active for ethanol and CO oxidation. After loaded with PdO, the catalytic activity enhances effectively. Combined the ethanol and CO oxidation activity with CO-TPD and ethanol-TPSR profiles, we can find the more intensive of CO₂ desorption peaks, the higher it is for the oxidation of CO and ethanol. Conversion versus yield plot shows the acetaldehyde is the primary product, the secondary products are acetic acid, ethyl acetate and ethylene, and the final product is CO₂. A simplified reaction scheme (not surface mechanism) is suggested that ethanol is first oxidized to form intermediate of acetaldehyde, then acetic acid, ethyl acetate and ethylene formed going with the formation of acetaldehyde, acetic acid, ethyl acetate; finally these byproducts are further oxidized to produce CO₂. PdO/Ce_0.75Zr_0.25O₂ catalyst has much higher catalytic activity not only for the oxidation of ethanol but also for CO oxidation. Thus the CO poison effect on PdO/Ce_0.75Zr_0.25O₂ catalysts can be decreased and they have the feasibility for application in direct alcohol fuel cell (DAFC) with high efficiency.