甲烷氧化偶联W-Mn催化剂的制备及表征

Preparation and Characterization of Catalyst for Oxidative Coupling of Methane

本文详细报道了制备因素对Na-W-Mn—O/SiO_2催化剂反应性能的影响,并用O_2-TPD,XRD,FT-IR,LRS等方法对催化剂进行了表征。结果表明,该催化剂的最佳组成是Mn 0.32wt％—Na_2WO_4 4wt％/SiO_2,由混浆法制备的催化剂具有较好的稳定性,连续反应30 h后,其甲烷转化活性和C_2烃收率均保持不变。催化剂的结构研究表明,Na_2WO_4与SiO_2发生了相互作用,形成有Si参与的表面钨氧物种,该催化剂具有较好的催化活性与表面钨氧物种的形成相关联,Mn的加入,可能大大提高了该催化剂中表面晶格氧的浓度,从而加快了CH_4的活化速度。

In this paper, the effects of preparation factors on OCM reactivity of Na-W-Mn-O/SiO2 catalyst were investigated. The activity of the catalyst was evaluated in a quartz fixed- bed reactor at atmospheric pressure. The catalyst was characterized by O2-TPD, XRD, FT-IR and LRS. The catalyst was prepared by two different methods-impregnating and physical mixing. The results show that the optimum contents of Na2WO4and Mn are 4 wt% and 0. 32 wt% respectively. Comparison of the catalyst prepared by mixing with the catalyst prepared by impregnating shows the former to be more stable. During the period of 30 h reaction , the catalytic behaviors remained unchanged. Structural studies of the catalyst indicated that the interaction between Na2WO4 and SiO2 has taken place. A W - O - Si species has formed and is related to the good catalytic behavior of OCM observed. The results of O2-TPD confirmed that the lattice oxygen is the active oxygen species for OCM. Small additions of Mn to the catalyst are shown to increase the concentration of surface lattice oxygen of the catalyst, so the activation of CH4 becomes faster.