Li-Mn/WO_(3)/TiO_(2)固体酸催化剂的制备及其甲烷氧化偶联催化性能研究北大核心CSCD

Li-Mn/WO_(3)/TiO_(2)催化剂具有良好的低温OCM催化性能,采用浸渍法制备Li-Mn/WO_(3)/TiO_(2)催化剂,并详细考察WO_(3)对催化剂物理化学性质及催化性能的影响.利用X射线衍射(XRD)、CO_(2)程序升温脱附(CO_(2)-TPD)、O_(2)程序升温脱附(O_(2)-TPD)、H_(2)程序升温还原(H_(2)-TPR)、拉曼光谱(Raman)和X射线光电子能谱(XPS)等表征技术对催化剂进行了研究,发现WO_(3)的添加提高了C_(2)选择性,并有效抑制了深度氧化.XRD与CO_(2)-TPD结果表明,WO_(3)的添加不仅有利于金红石型TiO_(2)的形成而且能够中和催化剂表面的强碱位,从而抑制了深度氧化反应.O_(2)-TPD和H_(2)-TPR结果表明,WO_(3)的添加降低了晶格氧(O^(2-))移动性,进而提高了反应的C_(2)选择性.此外,WO_(3)的添加促使了低温氧化偶联活性物种MnTiO_(3)的形成并提高了活性物种的分散性,因此提高了催化剂甲烷氧化偶联的反应活性和选择性.所有Li-Mn/x%WO_(3)/TiO_(2)催化剂中,Li-Mn/5%WO_(3)/TiO_(2)催化剂显示出最佳的OCM反应性能.在750℃,CH_(4)∶O_(2)∶N_(2)=10∶4∶5,GHSV=2280 mL·g^(-1)·h^(-1)条件下,最高的C_(2)产物收率可达16.3%.

Excellent Effect of Solid Acids Based on WO3/TiO2-supportedlithium-manganeseoxides for Oxidative Coupling of Methane

A series of novel solid acid catalysts based on WO3/TiO2-supported lithium-manganese oxides (Li-Mn/WO3/TiO2) with different WO3 loadings was prepared. The prepared catalysts were characterized via X-ray diffraction (XRD), CO2-temperature programmed desorption (CO2-TPD), O2-temperature programmed desorption (O2-TPD), and H2-temperature programmed reduction (H2-TPR) to elucidate the effect of WO3 loading on the catalyst properties and catalytic performance. The XRD and CO2-TPD results revealed that the WO3loading tended to promote the transformation of the anatase TiO2 to rutile TiO2 and reduced the number of strong basic sites, which suppressed the formation of completely oxidized CO2. Moreover, the O2-TPD and H2-TPR results revealed that the mobility of the O2- species was reduced in the Li-Mn/WO3/TiO2 catalysts. Thus, the Li-Mn/WO3/TiO2 catalysts with different WO3 loadings realized much higher C2 (ethylene, ethane) selectivity than the pure Li-Mn/TiO2, which was beneficial to the oxidative coupling of methane (OCM). Moreover, the WO3 loading enhanced the OCM catalytic performance of the Li-Mn/WO3/TiO2 catalyst by promoting the generation of MnTiO3 and contributing to the better dispersion of the active components on the catalyst surface. Owing to the synergistic interaction of the above factors, the Li-Mn/5%WO3/TiO2 catalyst exhibited the best performance among all the catalysts, giving the highest C2 yield of 16.3% , at 750?°C.