Oliver Christian Gobin
Research interests
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InterestsHeterogeneous Catalysis
Publications
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3.45Impact points
Nanoporous glass as a model system for a consistency check of the different techniques of diffusion measurement.
Chemphyschem : a European journal of chemical physics and physical chemistry. 03/2011; 12(6):1130-4.
The remarkable differences in the guest diffusivities in nanoporous materials commonly found with the application of different measuring techniques are usually ascribed to the existence of a hierarchy of transport resistances in addition to the diffusional resistance of the pore system and their dif... [more] The remarkable differences in the guest diffusivities in nanoporous materials commonly found with the application of different measuring techniques are usually ascribed to the existence of a hierarchy of transport resistances in addition to the diffusional resistance of the pore system and their differing influence due to the differing diffusion path lengths covered by the different measuring techniques. We report diffusion measurements with nanoporous glasses where the existence of such resistances could be avoided. Molecular propagation over diffusion path lengths from hundreds of nanometers up to millimeters was thus found to be controlled by a uniform mechanism, appearing in coinciding results of microscopic and macroscopic diffusion measurement.
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11.83Impact points
Enhancement of Sorption Processes in the Zeolite H-ZSM5 by Postsynthetic Surface Modification.
Angewandte Chemie (International ed. in English). 01/2009;
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3.45Impact points
On the Suitability of Different Representations of Solid Catalysts for Combinatorial Library Design by Genetic Algorithms.
Journal of combinatorial chemistry. 09/2008;
Genetic algorithms are widely used to solve and optimize combinatorial problems and are more often applied for library design in combinatorial chemistry. Because of their flexibility, however, their implementation can be challenging. In this study, the influence of the representation of solid cataly... [more] Genetic algorithms are widely used to solve and optimize combinatorial problems and are more often applied for library design in combinatorial chemistry. Because of their flexibility, however, their implementation can be challenging. In this study, the influence of the representation of solid catalysts on the performance of genetic algorithms was systematically investigated on the basis of a new, constrained, multiobjective, combinatorial test problem with properties common to problems in combinatorial materials science. Constraints were satisfied by penalty functions, repair algorithms, or special representations. The tests were performed using three state-of-the-art evolutionary multiobjective algorithms by performing 100 optimization runs for each algorithm and test case. Experimental data obtained during the optimization of a noble metal-free solid catalyst system active in the selective catalytic reduction of nitric oxide with propene was used to build up a predictive model to validate the results of the theoretical test problem. A significant influence of the representation on the optimization performance was observed. Binary encodings were found to be the preferred encoding in most of the cases, and depending on the experimental test unit, repair algorithms or penalty functions performed best.
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Mesostructured silica SBA-16 with tailored intrawall porosity part 2: Diffusion
Journal of Physical Chemistry C. 01/2007; 111(7):3059-3065.
In this Part 2 of the present work, the diffusivities of n-heptane, cumene, and mesitylene in the SBA-16 silica samples described in Part I have been measured by the zero length column (ZLC) method. A comparison is made between the diffusivities and diffusion apparent activation energies in these ma... [more] In this Part 2 of the present work, the diffusivities of n-heptane, cumene, and mesitylene in the SBA-16 silica samples described in Part I have been measured by the zero length column (ZLC) method. A comparison is made between the diffusivities and diffusion apparent activation energies in these materials and in a series of SBA-15 samples of similar pore size and pore volume. The latter series was discussed in a previous work. Clear differences are indeed observed and rationalized in terms of differences in the pore structure of the two series of solids.
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3.45Impact points
Comparison of single- and multiobjective design of experiment in combinatorial chemistry for the selective dehydrogenation of propane.
Journal of combinatorial chemistry. 11(5):907-13.
Two genetic algorithms for the single- and multiobjective design of combinatorial experiments were applied to the optimization of a solid catalyst system active in the selective catalytic oxidation of propane to propylene. The two different optimization strategies, namely, the single objective optim... [more] Two genetic algorithms for the single- and multiobjective design of combinatorial experiments were applied to the optimization of a solid catalyst system active in the selective catalytic oxidation of propane to propylene. The two different optimization strategies, namely, the single objective optimization of the yield and the multiobjective optimization of the conversion and selectivity were implemented and compared. It was observed that the multiobjective approach optimized the yield in a similar way compared to the single objective approach. With respect to the selectivity, however, the multiobjective outperformed the single objective approach. It was also found that by applying the multiobjective optimization more interesting possible combinations were discovered.
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Multi-objective optimization in combinatorial chemistry applied to the selective catalytic reduction of NO with C3H6
Journal of Catalysis.
A high-throughput approach, aided by multi-objective experimental design of experiments based on a genetic algorithm, was used to optimize the combinations and concentrations of a noble metal–free solid catalyst system active in the selective catalytic reduction of NO with C3H6. The optimization fra... [more] A high-throughput approach, aided by multi-objective experimental design of experiments based on a genetic algorithm, was used to optimize the combinations and concentrations of a noble metal–free solid catalyst system active in the selective catalytic reduction of NO with C3H6. The optimization framework is based on PISA [S. Bleuler, M. Laumanns, L. Thiele, E. Zitzler, Proc. of EMO'03 (2003) 494], and two state-of-the-art evolutionary multi-objective algorithms—SPEA2 [E. Zitzler, M. Laumanns, L. Thiele, in: K.C. Giannakoglou, et al. (Eds.), Evolutionary Methods for Design, Optimisation and Control with Application to Industrial Problems (EUROGEN 2001), International Center for Numerical Methods in Engineering (CIMNE), 2002, p. 95] and IBEA [E. Zitzler, S. Künzli, Conference on Parallel Problem Solving from Nature (PPSN VIII), 2004, p. 832]—were used for optimization. Constraints were satisfied by using so-called “repair algorithms.” The results show that evolutionary algorithms are valuable tools for screening and optimization of huge search spaces and can be easily adapted to direct the search towards multiple objectives. The best noble metal free catalysts found by this method are combinations of Cu, Ni, and Al. Other catalysts active at low temperature include Co and Fe.
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Multi-objective optimization in combinatorial chemistry applied to the selective catalytic reduction of NO with C3H6
JOURNAL OF CATALYSIS. 252(2):205-214.
A high-throughput approach, aided by multi-objective experimental design of experiments based on a genetic algorithm, was used to optimize the combinations and concentrations of a noble metal-free solid catalyst system active in the selective catalytic reduction of NO with C3H6. The optimization fra... [more] A high-throughput approach, aided by multi-objective experimental design of experiments based on a genetic algorithm, was used to optimize the combinations and concentrations of a noble metal-free solid catalyst system active in the selective catalytic reduction of NO with C3H6. The optimization framework is based on PISA [S. Bleuler, M. Laumanns, L. Thiele, E. Zitzler, Proc. of EMO'03 (2003) 4941, and two state-of-the-art evolutionary multi-objective algorithms-SPEA2 [E. Zitzler, M. Laumanns, L. Thiele, in: K.C. Giannakoglou, et al. (Eds.), Evolutionary Methods for Design, Optimisation and Control with Application to Industrial Problems (EUROGEN 2001), International Center for Numerical Methods in Engineering (CIMNE), 2002, p. 95] and IBEA [E. Zitzler, S. Kunzli, Conference on Parallel Problem Solving from Nature (PPSN VIII), 2004, p. 832]-were used for optimization. Constraints were satisfied by using so-called "repair algorithms." The results show that evolutionary algorithms are valuable tools for screening and optimization of huge search spaces and can be easily adapted to direct the search towards multiple objectives. The best noble metal free catalysts found by this method are combinations of Cu, Ni, and Al. Other catalysts active at low temperature include Co and Fe. (C) 2007 Elsevier Inc. All rights reserved.
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Comparison of the Transport of Aromatic Compounds in Small and Large MFI Particles
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 the frequency response method. Analysis of the experimental data in combination with the theoretical model... [more] 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 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.
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Influence of Postsynthetic Surface Modification on Shape Selective Transport of Aromatic Molecules in HZSM-5
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 surface modification. Postsynthetic modification of H-ZSM5 with a mesoporous silica overlayer generates novel... [more] 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 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.
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Mesostructured silica SBA-16 with tailored intrawall porosity part 1: Synthesis and characterization
JOURNAL OF PHYSICAL CHEMISTRY C. 111(7):3053-3058.
Mesostructured silica materials of SBA-16 type were synthesized under varying conditions affecting the pore size distribution. The alpha(s)-plot method allows us to identify two populations of intrawall pores and measure their respective specific volumes. A semiquantitative treatment of these data y... [more] Mesostructured silica materials of SBA-16 type were synthesized under varying conditions affecting the pore size distribution. The alpha(s)-plot method allows us to identify two populations of intrawall pores and measure their respective specific volumes. A semiquantitative treatment of these data yields an estimate for the intrawall pore radius. These results are discussed and related to the behavior of the long polar chains of the F127 surfactant in the synthesis gel.
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Role of the Surface Modification on the Transport of Hexane Isomers in ZSM-5
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 is enhanced by this modification, if the initial adsorption is the limiting step, i.e., for n-hexane, 2-me... [more] 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 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.
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CATL 29-Computational approaches toward HTE in heterogeneous catalysis
ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY. 235.
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Diffusion pathways of benzene, toluene and p-xylene in MFI
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. For zeolite crystals above 5 mu m average diameter, the transport in the zeolite pores exerts a significant eff... [more] 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. 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.
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A comparative study of diffusion of benzene/p-xylene mixtures in MFI particles, pellets and grown membranes
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 to isolated ZSM-5 crystallites. The kinetics of the transport in the pressed pellet and the grown membrane det... [more] 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 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.
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PETR 41-Role of transport processes on the shape selective properties of HZSM-5
ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY. 235.
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Diffusion in Circularly Ordered Mesoporous Silica Fibers
JOURNAL OF PHYSICAL CHEMISTRY C. 115(17):8602-8612.
Transport processes of n-hexane and mesitylene in circularly ordered mesoporous silica fibers have been investigated. Combining theoretical calculations based on the complex hierarchical structure with experimental results from frequency response experiments, three well-defined pathways for the tran... [more] Transport processes of n-hexane and mesitylene in circularly ordered mesoporous silica fibers have been investigated. Combining theoretical calculations based on the complex hierarchical structure with experimental results from frequency response experiments, three well-defined pathways for the transport pathways of molecules in the ordered mesoporous silica fibers are identified, that is, diffusion in axial, tangential, and radial directions, all occurring in parallel. The radial diffusion is the dominant process and is governed by intrawall transport. Transport in the axial direction overlaps with the radial diffusion and can be governed by either intrawall or mesopore transport. Cracks or defects at the surface enable diffusion in the tangential direction, which is the third kinetic process experimentally observed.
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Adsorption of C2-C8 n-Alkanes in Zeolites
JOURNAL OF PHYSICAL CHEMISTRY C. 115(4):1204-1219.
Adsorption of n-alkanes has been studied in the industrially relevant zeolites H-FAU, H-BEA, H-MOR, and H-ZSM-5 combining QM-Pot(MP2//B3LYP) with statistical thermodynamics calculations and assuming a mobile adsorbate. In H-ZSM-5, adsorption at the intersection site with the hydrocarbon chain extend... [more] Adsorption of n-alkanes has been studied in the industrially relevant zeolites H-FAU, H-BEA, H-MOR, and H-ZSM-5 combining QM-Pot(MP2//B3LYP) with statistical thermodynamics calculations and assuming a mobile adsorbate. In H-ZSM-5, adsorption at the intersection site with the hydrocarbon chain extending in the straight channel (SC+I) as well as in the zigzag channel (ZC+I) has been studied. In addition, differential heats of adsorption and adsorption isotherms at temperatures from 301 to 400 K of all C3-C6 n-alkane in H-ZSM-5 have been measured simultaneously via calorimetry and gravimetry. Calculated adsorption enthalpies are independent of temperature and are virtually identical to the adsorption energies. The adsorption strength increases in the order H-FAU < H-BEA < H-MOR < H-ZSM-5 (SC+I) < H-ZSM-5 (ZC+I) and varies linearly with the carbon number. As compared to experimental values, the calculated adsorption strength is overestimated by some 2 kJ mol(-1)/CH2 in FAU up to some 4 kJ mol(-1)/CH2 in H-ZSM-5 suggesting that the QM-Pot(MP2//B3LYP) calculations overestimate van der Waals stabilizing interactions and a correction term has been proposed. Adsorption entropy losses are independent of temperature and increase in the order H-FAU < H-BEA < H-MOR < H-ZSM-5 (SC+I) < H-ZSM-5 (ZC+I), according to the pore size of the zeolites. The calculated adsorption entropies agree nicely with available experimental results in all zeolites. QM-Pot(MP2//B3LYP) calculated adsorption equilibrium coefficients (using the corrected adsorption enthalpies) correspond relatively well to experimentally determined values. Comparison of relative turnover frequencies with relative adsorption equilibrium coefficients indicates that the variation of the equilibrium coefficient with the carbon number or with the zeolite can only partly explain the observed reactivity differences in monomolecular cracking of n-alkanes. In agreement with experimental observations, our results indicate that the difference in reactivity of the n-alkanes for monomolecular cracking in a given zeolite mainly originates from a difference in intrinsic monomolecular cracking rate coefficients.
