对甲烷氧化偶联W－Mn／SiO＿2催化剂Na＿2WO＿4的流失及其影响的考察

Loss of Na 2WO 4 and It′s Influence on the Oxidative Coupling of Methane on W Mn/SiO 2 Catalyst

用ＸＲＤ、ＦＴ－ＩＲ、ＥＳＲ、Ｈ２－ＴＰＲ和ＴＰＯ等方法，对Ｎａ２ＷＯ４－Ｍｎ２Ｏ３／ＳｉＯ２催化剂和其经水煮处理的一系列样品进行了表征．实验发现该催化剂中的结晶态Ｎａ２ＷＯ４易于流失，单层分布的Ｎａ２ＷＯ４在苛刻的处理条件下也有可能流失．依此，探讨了上述流失现象与Ｎａ２ＷＯ４－Ｍｎ２Ｏ３／ＳｉＯ２催化剂的催化活性及该催化剂在长时间反应中发生的ＳｉＯ２相变之间的关系，证明了结晶态Ｎａ２ＷＯ４的流失对该催化剂甲烷氧化偶联反应的催化活性只有轻微的影响，单层分布Ｎａ２ＷＯ４的流失可造成催化剂中Ｍｎ从Ｍｎ３＋转变为Ｍｎ２＋，并使催化剂的催化活性明显降低．但在水煮条件下，无论是结晶态的还是单层分布。

In this paper, the fresh and used Na 2WO 4 Mn 2O 3/SiO 2 catalysts and the samples treated in boiling water have been characterized by XRD, FT IR, ESR, H 2 TPR and O 2 TPO (Temperature programmed oxidation)techniques. The results show that the crystalline Na 2WO 4 phase is lost easily and monolayer distributed Na 2WO 4 is perhaps lost under the cruel conditions. The relations between Na 2WO 4 loss and catalyst activity as well as the SiO 2 phase transformation after long period reaction have been discussed. The studies indicate that the loss of crystalline Na 2WO 4 has little influence on the activity, but the loss of monolayer distributed Na 2WO 4 can result in the reduction of Mn 3+ to Mn 2+ causing the catalyst activity reduced markedly. However, the loss of either the crystalline or the monolayer Na 2WO 4 has no influence on the SiO 2 phase structure under the condition of boiling water treatment.