Browsing by Author "Möller, K"
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- ItemRestrictedThe characterization and elimination of the external acidity of ZSM-5.(Elsevier, 1996) Weber, R; Fletcher, J; Möller, K; O'Connor, CThe external acidity of ZSM-5 was modified either by coating the crystals with a silicalite shell or by chemical vapour deposition (CVD) of tetraethoxysilane (TEOS). Temperature programmed desorption (TPD) techniques were used to characterize the acidity changes arising from these modifications. Ammonia and pyridine were used as probes for the total acidity, and 4-methylquinoline was used to probe the external acidity of the modified and unmodified ZSM-5 samples. Si/Al ratios of the modified samples were also used to characterize the samples. Both methods of modification were able to make the external acid sites inert. Chemical vapour deposition was found to be a better method, because the external surface acidity was eliminated without significantly changing the catalyst in terms of total acidity. Optimum elimination of the external surface acidity by CVD was obtained for the sample with the higher deposition time (16 h) and temperature (400°C). Optimum elimination of the external surface acidity using the silicalite shell method was obtained using the detemplated NH4-form of the parent crystal as seed material. The channel structures of crystals modified by both processes remained accessible to ammonia and pyridine.
- ItemRestrictedEffects of in-situ chemical vapour deposition using tetraethoxysilane on the catalytic and sorption properties of ZSM-5.(Elsevier, 1998) Röger, H; Krämer, M; Möller, K; O'Connor, CThe external surface of HZSM-5 crystals was gradually modified by in-situ CVD of tetraethoxysilane. Using the particular procedures described in the paper, it was shown from probe reactions in combination with sorption studies that the external surface was deactivated and the pore-opening size was reduced while the intracrystalline pore space remained unmodified. The positive effect of the CVD treatment procedure on the shape selective properties of HZSM-5 was demonstrated by an enhancement in p-selectivity during toluene disproportionation. The paper discusses the relation between the effects of the CVD treatment procedure on catalytic properties, sorption properties and structural properties and conclusions are made on the use of the conversion of 1,2,4-trimethylbenzene, 1,3,5-triisopropylbenzene, toluene and n-hexane, respectively, to probe the effects of external surface modifications on properties of ZSM-5.