Methane dehydro-aromatization over Co-modified Mo/MCM-22 catalysts in the absence of oxygen and coke deposition

Mo/MCM-22 is a new type catalyst for methane dehydro-aromatization in the a bsence of oxygen, over which methane can be converted to aromatics with hig h benzene selectivity and catalytic stability. In this topic, we mainly dis cuss 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 s econd with Co (Co-Mo/MCM-22) results in better catalytic stability with a C o/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 th ere 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-b urning 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 ca ges.