Abstract
Pd/YZ-Al 2O 3 (Y and Zr modified Al 2O 3, and hereafter, labelled as Al) catalysts with 4 wt% additive CeO 2 and/or La 2O 3 were prepared and characterized by X-ray photoelectron spectroscopy (XPS), NO-temperature programmed desorption (NO-TPD), N 2-adsorption/desorption (Brunauer-Emmet-Teller BET method), X-ray diffraction (XRD) and CO-chemisorption. Catalytic activities for CH 4, CO and NO conversion were tested in a gas mixture simulated the emissions from natural gas vehicles (NGVs) operated under stoichiometric conditions. The results indicated that all catalysts exhibited excellent catalytic performances for CH 4 and CO oxidation and the promoting effect of CeO 2 or La 2O 3 was significant for NO conversion. XPS results showed that the electron density around Pd was increased by CeO 2 and/or La 2O 3, the binding energy of Pd 3d decreased as the order: Pd/Al > Pd/Ce/Al > Pd/La/Al > Pd/CeLa/Al. The electron-rich Pd showed Rh-like catalytic properties which exhibited good activity for the reduction of NO. NO-TPD results showed that the addition of CeO 2 and/or La 2O 3 increased NO adsorption on surface, and promoted the conversion of NO.
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