Design Strategies for CeO2鈥揗oO3 Catalysts for DeNOx and Hg0 Oxidation in the Presence of HCl: The Significance of the Surface Acid鈥揃ase Properties

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• 作者：Huazhen Chang ; Qingru Wu ; Tao Zhang ; Mingguan Li ; Xiaoxu Sun ; Junhua Li ; Lei Duan ; Jiming Hao
• 刊名：Environmental Science & Technology
• 出版年：2015
• 出版时间：October 20, 2015
• 年：2015
• 卷：49
• 期：20
• 页码：12388-12394
• 全文大小：399K
• ISSN：1520-5851

文摘

A series of CeMoO_x catalysts with different surface Ce/Mo ratios was synthesized by a coprecipitation method via changing precipitation pH value. The surface basicity on selective catalytic reduction (SCR) catalysts (CeMoO_x and VMo/Ti) was characterized and correlated to the durability and activity of catalyst for simultaneous elimination of NO_x and Hg⁰. The pH value in the preparation process affected the surface concentrations of Ce and Mo, the Brunauer-Emmett-Teller (BET) specific surface area, and the acid鈥揵ase properties over the CeMoO_x catalysts. The O 1s X-ray photoelectron spectroscopy (XPS) spectra and CO₂-temperature programmed desorption (TPD) suggested that the surface basicity increased as the pH value increased. The existence of strong basic sites contributed to the deactivation effect of HCl over the VMo/Ti and CeMoO_x catalysts prepared at pH = 12. For the CeMoO_x catalysts prepared at pH = 9 and 6, the appearance of surface molybdena species replaced the surface 鈭扥H, and the existence of appropriate medium-strength basic sites contributed to their resistance to HCl poisoning in the SCR reaction. Moreover, these sites facilitated the adsorption and activation of HCl and enhanced Hg⁰ oxidation. On the other hand, the inhibitory effect of NH₃ on Hg⁰ oxidation was correlated with the competitive adsorption of NH₃ and Hg⁰ on acidic surface sites. Therefore, acidic surface sites may play an important role in Hg⁰ adsorption. The characterization and balance of basicity and acidity of an SCR catalyst is believed to be helpful in preventing deactivation by acid gas in the SCR reaction and simultaneous Hg⁰ oxidation.