J.A. Lercher

Publications of J.A. Lercher

• Activation and isomerization of n-butane on sulfated zirconia model systems--an integrated study across the materials and pressure gaps.

  Authors: C. Breitkopf, H Papp, X Li, R Olindo, J.A. Lercher, R Lloyd, S Wrabetz, F C Jentoft, K Meinel, S Förster, K-M Schindler, H Neddermeyer, W Widdra, A Hofmann, J Sauer

  Physical chemistry chemical physics : PCCP. 08/2007; 9(27):3600-18.

  Butane activation has been studied using three types of sulfated zirconia materials, single crystalline epitaxial films, nanocrystalline films, and powders. A surface phase diagram of zirconia inButane activation has been studied using three types of sulfated zirconia materials, single crystalline epitaxial films, nanocrystalline films, and powders. A surface phase diagram of zirconia in interaction with SO(3) and water was established by DFT calculations, which was verified by LEED investigations on single-crystalline films and by IR spectroscopy on powders. At high sulfate surface densities a pyrosulfate species is the prevailing structure in the dehydrated state; if such species are absent, the materials are inactive. Theory and experiment show that the pyrosulfate can react with butane to give butene, H(2)O and SO(2), hence butane can be activated via oxidative dehydrogenation. This reaction occurred on all investigated materials; however, isomerization could only be proven for powders. Transient and equilibrium adsorption measurements in a wide pressure and temperature range (isobars measured via UPS on nanocrystalline films, microcalorimetry and temporal analysis of products measurements on powders) show weak and reversible interaction of butane with a majority of sites but reactive interaction with <5 micromol g(-1) sites. Consistently, the catalysts could be poisoned by adding sodium to the surface in a ratio S/Na = 35. Future research will have to clarify what distinguishes these few sites.

• On the sticking probability of aromatic molecules on zeolites. Comment on "Sticking probability on zeolites".

  Authors: A. Jentys, R R Mukti, J.A. Lercher

  The journal of physical chemistry. B. 10/2006; 110(35):17691-3; discussion 17694-5.

• Surface processes during sorption of aromatic molecules on medium pore zeolites.

  Authors: A. Jentys, H Tanaka, J.A. Lercher

  The journal of physical chemistry. B. 03/2005; 109(6):2254-61.

  The elementary steps of sorption and transport of benzene, toluene, and o- and p-xylene from the gas phase to hydroxy groups of zeolite H/ZSM-5 on the outer surface (SiOH groups) and in the poresThe elementary steps of sorption and transport of benzene, toluene, and o- and p-xylene from the gas phase to hydroxy groups of zeolite H/ZSM-5 on the outer surface (SiOH groups) and in the pores (SiOHAl groups) were studied using pressure modulations followed by fast time-resolved IR spectroscopy. Sorption on these acid sites occurs via a common physisorbed state on the outer surface. The equilibration of the molecules in this state is fast compared to the sorption rates on SiOH and SiOHAl groups. The relative rates of equilibration of functional groups with the aromatic molecules suggest that the aromatic molecules move freely on the surface of the outer surface before reversibly binding to OH groups, entering the micropores or desorbing. Molecules able to enter into the pores (benzene, toluene, p-xylene) adsorb faster on SiOHAl groups than on SiOH groups. If the access of the molecules into the pores is sterically constrained (o-xylene), the rate of adsorption on the remaining accessible SiOH groups is strongly enhanced.

• Hydrogenation of tetralin on silica–alumina-supported Pt catalysts I. Physicochemical characterization of the catalytic materials

  Authors: M.F. Williams, B. Fonfé, C. Sievers, A. Abraham, J.A. van Bokhoven, A. Jentys, J.A.R. van Veen, J.A. Lercher

  Journal of Catalysis.

  A series of well-defined catalysts based on platinum nanoparticles supported on amorphous silica–alumina with varying composition was prepared by incipient wetness impregnation. QuantitativeA series of well-defined catalysts based on platinum nanoparticles supported on amorphous silica–alumina with varying composition was prepared by incipient wetness impregnation. Quantitative structural characterization of alumina and aluminosilicate domains by 27Al (3Q) MAS NMR spectroscopy showed that the concentration of Brønsted acid sites determined by pyridine adsorption is related solely to the concentration of the aluminosilicate domain. However, only a very small fraction of the tetrahedrally coordinated aluminum led to the formation of Brønsted acid sites, because the negative charge on most of the tetrahedral Al–O was balanced by cationic aluminum oxide clusters. The preparation method led to small, uniform (0.6–0.8 nm) Pt particles on all aluminum-containing supports.

• Hydrogenation of tetralin on silica–alumina-supported Pt catalysts II. Influence of the support on catalytic activity

  Authors: M.F. Williams, B. Fonfé, C. Woltz, A. Jentys, J.A.R. van Veen, J.A. Lercher

  Journal of Catalysis.

  The interactions between an oxidic support and Pt particles were explored in a series of platinum catalysts supported on amorphous silica–alumina used for the hydrogenation of tetralin and theThe interactions between an oxidic support and Pt particles were explored in a series of platinum catalysts supported on amorphous silica–alumina used for the hydrogenation of tetralin and the hydrogenolysis of neopentane. The activity of the nanosized Pt particles increased with increasing intermediate electronegativity of the support for all supports with accessible Lewis acid sites. A compensation effect between the preexponential factor and the apparent energy of activation was observed for both reactions, attributed to the stronger adsorption of the reactants and intermediates on Pt induced by the increasingly electronegative supports. The product distribution in tetralin hydrogenation also points to stronger adsorption on Pt with increasing intermediate electronegativity of the support. X-ray absorption near-edge structure (XANES) findings indicate that the stronger interaction of the reactants is related to a reduced electron density on the platinum particles.

• Hydrogenation of tetralin on silica-alumina supported Pt catalysts II Influence of the Support on the Catalytic Activity

  Authors: M.F. Williams, B. Fonfe, C. Woltz, A. Jentys, J.A.R. van Veen, J.A. Lercher

  Journal of Catalysis 251(2007)497,506.

  Journal article

• Impact of supported ionic liquids on supported Pt catalysts

  Authors: R. Knapp, A. Jentys, J.A. Lercher

  Green Chem. 11(2009),656-661.

  Journal article

• Catalytically active sites of supported Pt catalysts for hydrogenation of tetralin in the presence of dibenzothiophene and quinoline

  Authors: M.F. Williams, B. Fonfe, A. Jentys, C. Breitkopf, J.A.R. van Veen, J.A. Lercher

  J. Phys. Chem. C 114(2010)34,14532-14541.

  Journal article

• Characterization of FeBEA and its activity in the NH3-SCR reaction 2010-03-10 - 2010-03-12

  Authors: S. Maier, A. Jentys, J.A. Lercher

  Poster

• On the nature of FeBEA active sites in NOx reduction with NH3 2010-07-04 - 2010-07-09

  Authors: S. Maier, A. Jentys, J.A. Lercher

  Poster

• 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.

• A comparative study of diffusion of benzene/p-xylene mixtures in MFI particles, pellets and grown membranes

  Authors: R. Kolvenbach, N. Al-Yassir, S. S. Al-Khattaf, O. C. Gobin, J. H. Ahn, A. Jentys, J. A. Lercher

  CATALYSIS TODAY. 168(1):147-157.

  The transport and separation of mixtures between benzene and p-xylene in pellets prepared by pressing of ZSM-5 powder and a dense supported (crystalline) Silicalite-1 membrane were compared toThe transport and separation of mixtures between benzene and p-xylene in pellets prepared by pressing of ZSM-5 powder and a dense supported (crystalline) Silicalite-1 membrane were compared to isolated ZSM-5 crystallites. The kinetics of the transport in the pressed pellet and the grown membrane determined in a Wicke-Kallenbach cell (313-403 K; partial pressure range 200-2300 Pa) differed significantly from those measured for isolated ZSM-5 particles with the pressure modulation frequency response technique (343-403 K; partial pressure 30 Pa). In a pressed pellet, the transport was of Knudsen type leading to high fluxes of 10(-4) mol/m(2) s and identical permeances for benzene and p-xylene. The diffusion coefficient in a pressed pellet exceeded that in particles, in which the transport was controlled by intracrystalline diffusion and the pore entrance step, by 8 orders of magnitude. The flux across a grown Silicalite-1 membrane was two orders of magnitude lower and the permeability of p-xylene was 2.6-5 times higher than that of benzene. The change in diffusivity in the membrane compared to the particles results from the higher surface coverage of p-xylene. (C) 2011 Elsevier B.V. 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.

• Hydrogenation of tetralin on silica-alumina supported Pt catalysts I - Physicochemical characterization of the catalytic materials

  Authors: M.F. Williams, B. Fonfe, C. Sievers, A. Abraham, J.A. vanBokhoven, A. Jentys, J.A.R. van Veen, J.A. Lercher

  Journal of Catalysis 251(2007)485,496.

  Journal article

• Improving bifunctional zeolite catalysts for alkane hydroisomerization via gas phase sulfation

  Authors: C. Woltz, A. Jentys, J.A. Lercher

  Journal of Catalysis 237(2006)1,337.

  Journal article

• Investigation of the adsorption of methanol on alkali metal cation exchanged zeolite X by inelastic neutron scattering

  Authors: R Schenkel, A. Jentys, S F Parker, J.A. Lercher

• INS and IR and NMR spectroscopic study of C1-C4 alcohols adsorbed on alkali metal exchanged zeolite X

  Authors: R Schenkel, A. Jentys, S F Parker, J.A. Lercher