Co改性Mo/MCM-22催化剂上甲烷无氧芳构化及积炭研究

Methane Dehydro-Aromatization over Co-Modified Mo/MCM-22 Catalysts in the Absence of Oxygen and Coke Deposition

研究了Co的添加对Mo/MCM 2 2催化剂甲烷无氧芳构化反应性能的影响 .发现用共浸渍法制备的Co/Mo摩尔比为 0 2的催化剂具有较高的活性 ,而先浸渍Mo后浸渍Co的催化剂具有较好的稳定性 .XRD实验表明 ,Co及Mo的氧化物均高度分散在分子筛表面 ,其担载降低了分子筛的衍射强度 .不同接触时间下催化剂的反应结果表明 ,接触时间长 ,积炭选择性随接触时间增加而迅速增加 ;接触时间短 ,积炭选择性随接触时间增加而减少 .积炭催化剂的TG研究表明 ,催化剂上的积炭主要有两种形式 .低温积炭随反应时间增加而迅速增多 ,高温积炭的变化则较为缓慢 .低温积炭可能是导致催化剂活化和失活的主要原因 .高温积炭可能是一种大分子量的碳氢物种 ,位于MCM 2 2分子筛的“超笼”中 ,表明MCM 2

Mo/MCM-22 is a new type catalyst for methane dehydro-aromatization in the absence of oxygen, over which methane can be converted to aromatics with high benzene selectivity and catalytic stability. In this topic, we mainly discuss the promotional effect by the addition of Co to the Mo/MCM-22 catalyst as the second component. It suggests that different steeping methods have different affection to the catalyst. Coimpregnating Co and Mo ((Co, Mo)/MCM-22) results in better catalytic activity while first dipping with Mo and second with Co (Co-Mo/MCM-22) results in better catalytic stability with a Co/Mo atomic, ratio of 0.2. X-ray diffraction results indicate that the CoO and MoO3 can be highly distributed on the MCM-22 zeolite and their loadings weaken the zeolite's X-ray diffraction peak intensity. The coke that forms at low space velocity is mainly the graphitic type coke and that forms at high space velocity is mainly the pre-graphitic type one, which plays a key role to the catalytic deactivation. Thermogravimetric studies show that there is mainly two types of coke on the catalysts. The easy-burning coke is the main type coke which leads to the catalytic deactivation and the hard-burning coke has no effect on the catalytic deactivation. Hard-burning coke may be a heavy-hydrocarbon type coke that locates in the zeolite's large cages.