Browsing by Author "Möller, K P"

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    The chemical vapour and liquid deposition of tetraethoxysilane on the external surface of ZSM-5
    (Elsevier, 1998) Weber, R W; Möller, K P; Unger, M; O'Connor, C
    The external acidity of ZSM-5 was modified by chemical vapour deposition (CVD) and chemical liquid deposition (CLD) of tetraethoxysilane [Si(OC2 H5 ) 4 ] using a static vacuum system, a vapour phase flow system and liquid phase deposition. Temperature programmed desorption (TPD) techniques were used to characterise the acidity changes arising from these modifications. Pyridine was used as a probe for the total acidity and 4-methyl quinoline (MQ) was used to probe the external acidity. The adsorption capacities of the samples were measured using n-hexane, p-xylene, o-xylene and 1,2,4-trimethyl benzene. The extent of Si(OC2 H5 ) 4 deposition was strongly dependent on temperature in both vapour phase flow and static vacuum systems. Continuous Si(OC2 H5 ) 4 deposition was observed in the presence of H2 O at relatively high temperatures when decomposition products were removed from the sample. It is proposed that physisorbed species need to be removed by evacuation or calcination to re-expose active sites, thereby enabling complete inertisation of the external surface acidity to occur, and that a more uniform covering can be obtained when a gradual deposition process is used. Such a process may be achieved by the use of diluents or by preventing overexposure of Si(OC2 H5 ) 4 to the sample under conditions where continuous deposition may occur. It was shown that it is possible to reduce the relative external surface acidity by 97% without significant changes in acidity as measured by Py-TPD or adsorption capacity.
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    Diffusion and adsorption in zeolite Y and mordenite deactivated by propene oligomerization and hexane cracking.
    (Elsevier, 1994) Möller, K P; Kojima, M; O'Connor, C T
    The bidisperse pore diffusion model applied to the pulse gas chromatography (PGC) technique was used to determine the effect of coke formation on the diffusion and adsorption of propane, n-butane and isobutane in the pores of zeolite Y (HY) and mordenite (HM) before and after deactivation during hexane cracking and propene oligomerization. The catalysts were characterized using TPD, TG/DTA, BET and pore volume measurements. Tracer diffusion measurements taken before and after reaction showed that in the case of hexane cracking over HY the diffusivity decreased by more than three orders of magnitude while the tracer adsorption equilibrium constant increased. In the case of HM, the diffusivity decreased by five orders of magnitude and the adsorption equilibrium constant also decreased by a factor of 10. In HY, deactivated during propene oligomerization, the diffusion was an order of magnitude faster than in the case of the catalyst deactivated by hexane cracking, while the adsorption equilibrium constant decreased. HM deactivated by oligomerization showed macropore behaviour. Proposals are made to explain the above observations.