材料期刊网

研究了Co的添加对Mo/MCM-22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-22分子筛的“超笼”中,表明MCM-22有较大的容积炭能力.

Mo/MCM-22 is a new type catalyst for methanedehydro-aromatization in the abse nce of oxygen, over which methane can be converted to aromatics with high benzen e selectivity and catalytic stability. In this topic, we mainly discuss the prom otional effect by the addition of Co to the Mo/MCM-22 catalyst as the second co mponent. It suggests that different steeping methods have different affection to the catalyst. Coimpregnating Co and Mo ((Co,Mo)/MCM-22) results in better cata lytic activity while first dipping with Mo and second with Co (Co-Mo/MCM-22) r esults in better catalytic stability with a Co/Mo atomic ratio of 0.2. X-ray d iffraction 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 graphiti c type coke and that forms at high space velocity is mainly the pre-graphitic t ype 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-bur ning coke may be a heavy-hydrocarbon type coke that locates in the zeolite's la rge cages.