掺杂碱金属与碱土金属的CuO-CeO_2催化剂的漫反射红外光谱分析

Study on CuO-CeO_2 Catalysts Doped with Alkali and Alkaline Earth Metal Oxides by In-Situ DRIFTS

CuO-CeO2系列催化剂是高效的CO选择性氧化反应的催化剂,通过原位漫反射红外光谱对掺杂碱金属和碱土金属氧化物的CuO-CeO2催化剂表面的吸附物种进行了研究。结果表明CuO-CeO2系列催化剂上,2 106 cm-1处出现CO的红外吸附峰。在反应气氛中,此峰的强度随着温度先升高后降低,说明Cu+是CO主要的活性吸附中心。低温下催化剂表面吸附的CO主要以可逆形式脱附出来,而高温下CO则以不可逆的形式脱附出来。催化剂表面在3 660 cm-1处出现尖锐的红外峰,归属于CeO2经还原产生的Ce-(OH)2偕式基团。在1 568,2 838和2 948 cm-1附近处出现甲酸根的红外谱峰,以及1 257和1 633 cm-1处出现碳酸根物种的红外峰。甲酸根物种是气相的CO与表面的羟基反应生成的产物,该物种的C—H键断裂生成碳酸根物种,这两物种均会降低催化剂的高温活性。Cu1Li1Ce9Oδ催化剂出现较强的CO2和甲酸根的红外峰,温度高于180℃时,该催化剂上还能看到微弱的CO红外峰,说明锂离子的给电子性质有利于提高Cu1Li1Ce9Oδ催化剂上CO的不可逆脱附,抑制氢的活化吸附,同时促进了甲酸根物种的生成。低温下Cu1Mg1Ce9Oδ和Cu1Ba1Ce9Oδ催化剂上CO的吸附量较多,但主要以可逆脱附形式脱附出来,对CO选择性氧化没有贡献。

CuO-CeO2 series catalysts are the effective catalysts for the selective CO oxidation in hydrogen-rich gas. The adsorption species on the CuO-CeO2 catalysts doped with alkali and alkaline earth metal oxides were investigated with in situ diffuse reflectance FTIR spectroscopy （in-situ DRIFTS） technique. The results showed that a bane at 2 106 cm^-1, due to the carbonyl species, appeared on the CuO-CeO2 catalysts. In the reaction atmosphere, the intensity of this band increased first and then decreased with increasing the temperatures. It was noted that the main active adsorption sites of the CuO-CeO2 catalysts were Cu^＋ species. At lower temperatures, the carbonyl species were desorbcd from the surface of CuO-CeO2 catalysts in the reversible form, while they were desorbed mainly in the irreversible form at thc higher temperatures. A sharp peak at 3 660 cm^-1 , attributed to the geminal Ce（OH）2 group, was also apparent on the surface of reduced CuO-CeO2 catalyst. The peaks at 1 568, 2 838 and 2 948 cm^-1 were attributed to formatc species and the peaks centered at 1 257 and 1 633 cm^-1 were assigned to carbonate species. CO could react with the active hydroxyl species and generate formate species. At higher temperatures, the C-H bond of formate species could break and form carbonate species. These two species would decrease the performance of CuO-CeO2 catalysts at higher temperatures. The stronger IR peaks attributed to CO2 and formate species were observed, moreover there was still a weak IR peak assigned to carbonyl species for Cu^＋ Li1 Ce9 Oδ catalyst when the temperature was above 180 ℃. It was shown that as the electron donor, the doping of Li2O on CuO-CeO2 catalyst could contribute to the irreversible desorption of CO at lower temperatures and inhibit the adsorption of Hz on the catalytic surface, and benefit the formation of formate species as well.Although the amounts of CO adsorption on CUl Mgl Ce9Oδ and Cu1 Ba1 Ce9Oδ catalysts were much more than other catalysts at lower temperatures, they were mainly desorbed in the reversible form, which had no contribution to the selective CO oxidation.