PETR 41 |
| Shape selective properties of HZSM-5 in xylene isomerization are usually associated with desorption barriers for bulky molecules. Post synthesis modification with tetraethylorthosilicate is employed to increase these diffusional constraints. Using fast time-resolved rapid scan IR spectroscopy, frequency response methods and transmission electron microscopy it is shown that the surface modification changes the sorption and desorption process in a more complex way than previously thought. At large, the surface modification leads to covering the crystal surface with a (partial) layer of amorphous SiO2. This impacts a series of processes related to the sticking coefficients of the adsorbing molecules, the diffusion across the outer surface and the process of entering the zeolite pores. The modification of the surface texture and the impact on the individual sorption processes (such as the improved sorption rates for lighter aromatics) are used to explain and optimize shape selective properties. |
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Zeolite Catalysis for Green Chemistry in Synthesis of Chemicals and Fuels
8:20 AM-12:10 PM, Monday, April 7, 2008 Morial Convention Center -- Rm. 346, Oral
Division of Petroleum Chemistry |