S. J. Reitmeier

Publications of S. J. Reitmeier

• Comparison of the Transport of Aromatic Compounds in Small and Large MFI Particles

  Authors: O. C. Gobin, S. J. Reitmeier, A. Jentys, J. A. Lercher

  JOURNAL OF PHYSICAL CHEMISTRY C. 113(47):20435-20444.

  The diffusion of alkyl-substituted aromatic molecules in two H-ZSM5 samples consisting of very small (< 100 nm) and large (similar to 3-4 mu m) primary particles was investigated by means of theThe diffusion of alkyl-substituted aromatic molecules in two H-ZSM5 samples consisting of very small (< 100 nm) and large (similar to 3-4 mu m) primary particles was investigated by means of the frequency response method. Analysis of the experimental data in combination with the theoretical modeling of the complete transport network shows that the details of the transport processes and the rate determining step depend on the particle size. With large particles, intracrystalline diffusion was rate determining for the overall diffusion, while for the small particles the diffusion was controlled by Surface effects.

• Influence of Postsynthetic Surface Modification on Shape Selective Transport of Aromatic Molecules in HZSM-5

  Authors: S. J. Reitmeier, O. C. Gobin, A. Jentys, J. A. Lercher

  JOURNAL OF PHYSICAL CHEMISTRY C. 113(34):15355-15363.

  Fast, time-resolved infrared spectroscopy was utilized to determine the transport and sorption properties of benzene, toluene, and p-xylene oil a series of zeolites with increasing degree of surfaceFast, time-resolved infrared spectroscopy was utilized to determine the transport and sorption properties of benzene, toluene, and p-xylene oil a series of zeolites with increasing degree of surface modification. Postsynthetic modification of H-ZSM5 with a mesoporous silica overlayer generates novel hierarchical materials. which significantly increase the sorption rates for benzene and decrease it gradually for alkyl-substituted aromatic molecules with increasing radius of gyration of the aromatic molecule. The ratio between the sorption rates of benzene and p-xylene increased from,in initial value of 4.3 to about 27 after modification. The reason for the enforced differentiation is the combination of the intrinsic size exclusion properties of the zeolite micropores and the variation of the sticking probability of the molecules on the modified surface, which enhanced the mass transfer into the porous overlayer. The size of the overlayer pores and the radius of gyration of the sorbate were identified as the parameters determining the sorption rates. Our results highlight that hierarchical composites generated by deposition of highly porous silica overlayers on microporous materials allow tailoring the separation properties of porous materials and allow introducing a new concept to kinetically separate molecules of identical minimum (kinetic) diameters.

• Role of the Surface Modification on the Transport of Hexane Isomers in ZSM-5

  Authors: O. C. Gobin, S. J. Reitmeier, A. Jentys, J. A. Lercher

  JOURNAL OF PHYSICAL CHEMISTRY C. 115(4):1171-1179.

  The role of the surface modification on the transport properties of nanosized HZSM-5 particles was investigated by the analysis of the sorption kinetics of hexane isomers. The rate of diffusion isThe role of the surface modification on the transport properties of nanosized HZSM-5 particles was investigated by the analysis of the sorption kinetics of hexane isomers. The rate of diffusion is enhanced by this modification, if the initial adsorption is the limiting step, i.e., for n-hexane, 2-methylpentane, and 3-methylpentane. If the intracrystalline transport is the rate-determining step, i.e., for 2,2-dimethylbutane, the surface modification leads to a significantly decreased sorption rate. This reduction in the transport rate is caused by a lower pre-exponential factor; i.e., it is entropically induced. Due to the surface modification, a certain fraction of the pores is completely blocked for the sterically demanding molecules reducing the probability of entering the pores. The results show that surface modification of microporous materials allows selectively enhancing or decreasing the transport rate of defined systems.

• Diffusion pathways of benzene, toluene and p-xylene in MFI

  Authors: O. C. Gobin, S. J. Reitmeier, A. Jentys, J. A. Lercher

  MICROPOROUS AND MESOPOROUS MATERIALS. 125(1-2, Sp. Iss. SI):3-10.

  The diffusion of alkyl-substituted aromatic molecules in H-ZSM-5 was investigated by means of the frequency response method decoupling particle size effects and intracrystalline diffusion. ForThe diffusion of alkyl-substituted aromatic molecules in H-ZSM-5 was investigated by means of the frequency response method decoupling particle size effects and intracrystalline diffusion. For zeolite crystals above 5 mu m average diameter, the transport in the zeolite pores exerts a significant effect on the overall transport causing anisotropic diffusion as the aspect ratio of the aromatic molecules increases. Diffusion of benzene is nearly isotropic, while p-xylene shows marked differences between the diffusive processes in the straight and sinusoidal channel system of ZSM-5. The isotropic diffusion of benzene is rationalized on the basis of its ability to reorient between the two channel systems without major hindrances. For p-xylene, switching between the channels is only possible by energetically unfavorable rotational motions leading to a low probability for changing between both channel systems. (C) 2009 Elsevier Inc. All rights reserved.

• PETR 41-Role of transport processes on the shape selective properties of HZSM-5

  Authors: S. J. Reitmeier, O. C. Gobin, A. Jentys, J. A. Lercher

  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY. 235.