Abstract
AbstractAbstract: We present the effect of different combinations of intracrystalline pore systems in hierarchical ZSM‐5 zeolites on their performance as MTO catalysts. We prepared ZSM‐5 zeolites with additional intracrystalline mesoporous, intracrystalline macropores and a novel ZSM‐5 type zeolite with intracrystalline meso and macropores. The catalytic results showed that both used catalysts with mesopores and macropores exhibited three times longer catalyst lifetime compared to a conventional catalyst. However, TGA analysis of the deactivated catalysts showed much larger coke content in the mesoporous catalyst than in the macroporous catalyst. Consequently, macropores predominantly led to reduced coke formation rate while additional mesopores predominantly enhanced the resistance against deactivation by coke. Combining both intracrystalline meso and macropores in one catalyst lead to a tenfold increase in catalyst lifetime. Besides the effect on the catalyst lifetime there was also a strong effect of the additional pore systems on the selectivity of the catalysts. The catalysts containing mesopores showed reduced selectivity to short chain olefins and increased selectivity to larger hydrocarbons in comparison to the catalysts without a mesopores system.
Highlights
While the well-ordered micropore system of zeolites has many advantages, the diffusion coefficients of molecules in the micropores are very low.[3]the utilisation of zeolites in catalysis is often limited by slow diffusion of reactant species to the active sites confined within the micropores and diffusion of products out of the micropore system
The utilisation of zeolites in catalysis is often limited by slow diffusion of reactant species to the active sites confined within the micropores and diffusion of products out of the micropore system
The second approach results in hierarchically structured zeolites which consist of at least one additional larger pore system interconnected to the zeolitic micropores.[5a,6]
Summary
While the well-ordered micropore system of zeolites has many advantages, the diffusion coefficients of molecules in the micropores are very low.[3]. Co or Fe based catalysts.[13] the Zeolites belong to the most important catalytic materials and find widespread application as heterogeneous catalysts for crude oil refining as well as for processes in petro chemistry and fine chemistry.[1] The crystalline framework of zeolites gives rise to micropores with diameters ranging from 0.3 to 1.2 nm This pore diameters, similar to the dimensions of molecules, give rise to the unique shape selective properties of zeolite catalysts.[2]. Hierarchically structured ZSM-5 zeolites (MFI topology) could already demonstrate drastically increased catalyst lifetimes in comparison to conventional, purely microporous zeolite catalysts in the MTH reaction.[19] until now, the focus of these studies was on mesoporous catalysts prepared by desilication or soft templating approaches.[18,20]. These catalysts were characterised and tested in the MTO reaction under the same reaction conditions
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