The Preparation Of Mesopore Containing And Modified ZSM-5Catalyst And Its Application In Methanol To Propylene (MTP) Reaction

Coal and natural gas serve as raw materials for the methanol conversion reactions. On one hand, based on China’s fossil fuel resource that coal is comparatively abundant and meanwhile crude oil is somehow in shortage, the combination of coalification and methanol conversion techniques will build a promising way for comprehensive application of fossil fuel resource, which is the way for China to avoid the potential risk from excessive dependence on crude oil especially the import from overseas, and ensure the national energy security; On the other hand, the market demand for propylene and its derivatives has been increasing rapidly during recent years which tightens the supply of propylene that mainly produced as a by-product of ethylene in the present days. Thus it is highly desired to develop a new route for the efficient manufacture of propylene, which has made methanol to propylene (MTP) technique draw plenty of attentions from the chemical industry. Therefore, the development of MTP technique for optimizing the production of propylene is endowed with economic and realistic significance.In order to alleviate the frustrating catalyst deactivation and further enhance the selectivity for propylene, a series of research work on the structure designing of the zeolite catalyst from the physical point of view, and on the metal modification of the zeolite support from the chemical property point of view has been carried out to obtain a highly efficient catalyst with high catalytic stability and propylene selectivity Thus, our research works concentrates on following fields:1) We have successfully introduced certain proportion of mesopores into the crystal of zeolite ZSM-5with a low Si/Al ratio via alkaline treatment desilication; it has been found that dealumination occurs along with the desilication process and correlation between dealumination and the zeolite acidity has been created; the prepared mesopore containing zeolite catalyst shows noticeable stability enhancement, which opens the possibility of application of mesoporous zeolite catalyst in MTP reaction. 2) Mesopore containing zeolite ZSM-5with a high Si/Al ration has been prepared through hard templating of CMK-3. The impact of structural property of the parent template SBA-15and the synthesis condition for zeolite ZSM-5on the preparation of mesoporous zeolite is investigated. The obtained mesoporous ZMS-5catalyst is applied in MTP reaction and shows remarkably prolonged catalytic lifetime.3) We have successfully prepared mesopore containing zeolite ZSM-5through in situ hydrothermal treatment of the solution containing alkali-dissolved SBA-15with the carbonized P123surfactant in the mesopores. The uniform dispersion as well as extraordinary hydrophilicity of the carbon template ensure its high efficiency in directing mesoporosity in the zeolite, while the silica obtained from alkali-dissolution are fully and directly used as the nutrition in zeolite crystallization. The composition and mesoporosity of the final zeolite product could be modulated facilely by adjusting the composition (e.g. Si/Al and C/Si ratios) of the synthesis gel. More importantly, the mesoZSM-5catalysts showed notable stability in MTP reaction due to their enlarged pore size and pore volume. Besides, this method can be easily extended to other types of zeolites for various reactions.4) The novel approach for catalyst anti-coking by way of dehydrogenation inhibition has been established in methanol to propylene reaction. Through the introduction of gold on zeolite ZSM-5, the catalytic stability of zeolite ZSM-5catalyst for methanol to propylene reaction has been distinctively enhanced. The effect of nano-gold lies in its unique chemical property to participate in the dehydrogenation process. Revealed by DFT calculations, the gold species stabilizes dehydrogenation intermediates, thus decelerating the dehydrogenation reaction. This dehydrogenation inhibition effect was also witnessed by the decreased coking rate on the catalyst as well as the adjusted selectivity of methane and monocyclic aromatics. These results provide a fresh aspect in designing catalysts not only for MTP reaction, but also for all acid-catalysed reactions annoyed by coking. 5) Catalytic performance of Ru and Pt modified ZSM-5catalyst has also been investigated. It was shown that the chemical state of the introduced metal species and the reduction condition act as important roles in determining its product selectivity.