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Guy Marin - One of the best experts on this subject based on the ideXlab platform.
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Physisorption and chemisorption of linear alkenes in zeolites a combined qm pot mp2 b3lyp gulp statistical thermodynamics study
2011Co-Authors: Cuong Manh Nguyen, Marie-françoise Reyniers, Bart De Moor, Guy MarinAbstract:Physisorption and chemisorption of C2–C8 linear alkenes in H–FAU, H–BEA, H–MOR, and H–ZSM-5 have been quantified up to 800 K by combining QM-Pot(MP2//B3LYP:GULP) with statistical thermodynamics calculations. The influence of the zeolite topology and the alkene CC double bond position on the alkene sorption thermodynamics is addressed on the basis of linear variations of sorption enthalpies and entropies as a function of the carbon number. The Physisorption strength and entropy losses increase in the order H–FAU < H–BEA < H–MOR < H–ZSM-5. Higher Physisorption strength is computed for 2-alkenes (H–MOR) and 2-, 3-, and 4-alkenes (H–ZSM-5) as compared with 1-alkenes. Protonation of physisorbed alkenes leads to significantly more stable alkoxides. In contrast to the Physisorption, higher chemisorption strength does not lead to larger chemisorption entropy losses. Also, the intrinsic stability of the alkoxides, i.e., relative to gas phase H2 and graphite, only depends on the carbon number and not on the detaile...
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normal mode analysis in zeolites toward an efficient calculation of adsorption entropies
2011Co-Authors: Bart De Moor, Marie-françoise Reyniers, An Ghysels, Veronique Van Speybroeck, Michel Waroquier, Guy MarinAbstract:An efficient procedure for normal-mode analysis of extended systems, such as zeolites, is developed and illustrated for the Physisorption and chemisorption of n-octane and isobutene in H-ZSM-22 and H-FAU using periodic DFT calculations employing the Vienna Ab Initio Simulation Package. Physisorption and chemisorption entropies resulting from partial Hessian vibrational analysis (PHVA) differ at most 10 J mol−1 K−1 from those resulting from full Hessian vibrational analysis, even for PHVA schemes in which only a very limited number of atoms are considered free. To acquire a well-conditioned Hessian, much tighter optimization criteria than commonly used for electronic energy calculations in zeolites are required, i.e., at least an energy cutoff of 400 eV, maximum force of 0.02 eV/A, and self-consistent field loop convergence criteria of 10−8 eV. For loosely bonded complexes the mobile adsorbate method is applied, in which frequency contributions originating from translational or rotational motions of the ad...
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Physisorption and chemisorption of alkanes and alkenes in h fau a combined ab initio statistical thermodynamics study
2009Co-Authors: Bart De Moor, Marie-françoise Reyniers, Guy MarinAbstract:The sorption in H-FAU zeolite of C4–C12 n-alkanes, and linear and branched C2–C8 alkenes has been quantified up to 800 K by combining QM-Pot(MP2//B3LYP) with statistical thermodynamics calculations. The Physisorption strength increases linearly with increasing carbon number by 8.5 kJ mol−1 and does not depend on the detailed alkane or alkene structure. Van der Waals interactions are dominant in Physisorption, but alkenes are additionally stabilized by 20 kJ mol−1 by formation of a π-complex. Protonation of an alkene leads to the formation of alkoxides, which are more stable than the physisorbed species. As for Physisorption a linear relation between the chemisorption energy and the carbon number is obtained. Protonation energies are independent of the carbon number but depend on the type of CC double bond being protonated. The relative stability difference between the secondary and tertiary alkoxides is 15 kJ mol−1 in favor of the former. Both Physisorption and chemisorption are accompanied with entropy losses which increase linearly with the carbon number. A typical compensation effect is obtained: the stronger the stabilization of the sorbed species the more pronounced the entropy loss. For temperatures ranging from 0 to 800 K, all of the derived linear relations expressing the Physisorption and/or chemisorption enthalpy and entropy of the alkanes and the alkanes as function of the carbon number are independent of temperature. A good agreement between calculated and experimental values for alkanes is obtained at 500 K.
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relumped single event microkinetic model for alkane hydrocracking on shape selective catalysts catalysis on zsm 22 pore mouths bridge acid sites and micropores
2004Co-Authors: C Laxmi S Narasimhan, Guy Marin, Johan A Martens, Joris W Thybaut, Joeri F M Denayer, Gino V Baron, P A JacobsAbstract:Abstract A relumped single-event microkinetic (SEMK) model is developed to describe alkane hydroconversion on shape-selective Pt-H/ZSM-22. The model, considers n -alkane, mono-, di- and tri-branched alkanes for each carbon number and is developed according to the reaction rules formulated for the molecular SEMK model on ZSM-22. Differences in Physisorption and protonation behaviour among the carbenium ions on ZSM-22 are accounted for. Reactions can occur at the pore mouth, bridge and micropore acid sites. Lumping coefficients depend on the type of sites. The calculation of the lumping coefficients is performed using a structural class based method, not requiring the generation of the detailed reaction network. The internal composition of a lump is determined by the Physisorption properties of the alkanes belonging to the lump. The hydrocracking of n -C6 to n -C18 alkanes is described adequately over a wide range of conversions.
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alkene protonation enthalpy determination from fundamental kinetic modeling of alkane hydroconversion on pt h us y zeolite
2001Co-Authors: Joris W Thybaut, Guy Marin, Gino Baron, Pierre Jacobs, Johan A MartensAbstract:Alkane, c.q., C5 to C12, hydrocracking was performed on Pt/H–Y-zeolite and on Pt/H–USY-zeolites with Si/Al ratio of 13 and 30 at temperatures of 506–563 K, pressures of 0.45–1.5 MPa, and molar hydrogen to hydrocarbon ratio's in the 4.23–250 range. The catalytic conversion was described with a fundamental molecular model, relying on experimentally determined Physisorption equilibria and on a network of elementary reactions according to the bifunctional reaction scheme. The three zeolite samples showed substantial differences in activity, but not in selectivity. The activity differences among the zeolites mainly resulted from differences in both the number of acid sites and the average acid strength, while differences in Physisorption effects for these zeolite samples were of minor importance. On each catalyst, the reactivity of alkanes increased with carbon number. This tendency was related to three phenomena: (1) Physisorption of heavier molecules was more favorable; (2) the reaction network and the number of parallel reactions became larger with larger molecules, and (3) in the range of carbon numbers from C5 to C8, the stabilization of alkylcarbenium ions and, hence, their concentration increased with increasing size and electron donating property of alkyl-substituents. The differences in average acid strength between the three catalysts were quantified with alkene protonation enthalpy values extracted from the model. The kinetic parameters obtained for a reference hydrocarbon component and a reference Pt/H–(US)Y-type zeolite are adaptable to any other hydrocarbon and any other Pt/H–(US)Y-type catalyst by adjusting the standard protonation enthalpy.
Katsuyuki Fukutani - One of the best experts on this subject based on the ideXlab platform.
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effects of rotational symmetry breaking on Physisorption of ortho and para h 2 on ag 111
2014Co-Authors: Toshiki Sugimoto, Katsuyuki FukutaniAbstract:Quantum-state-selective thermal desorption of ${\mathrm{H}}_{2}$ weakly physisorbed on Ag(111) demonstrates significantly different desorption features between the nuclear-spin modifications. An energy shift due to the rotational-symmetry breaking induced by an anisotropic interaction affects not only the enthalpy but also the entropy of adsorption. The preexponential factor for desorption of the ortho-${\mathrm{H}}_{2}$ is about three times as large as that of the para-${\mathrm{H}}_{2}$. The entropy difference indicates a perpendicular orientation preference of anisotropic Physisorption potential, which also suggests the importance of partial hybridization interaction for weak Physisorption.
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Physisorption and ortho para conversion of molecular hydrogen on solid surfaces
2013Co-Authors: Katsuyuki Fukutani, Toshiki SugimotoAbstract:Abstract Molecular hydrogen exists in nuclear-spin isomers of ortho and para species according to the total nuclear spin. These species are correlated to the rotational states with even and odd rotational quantum numbers because of the symmetry of the total wavefunction with respect to the permutation of the two nuclei. Although interconversion between the ortho and para states is extremely slow in an isolated state, the conversion is promoted in a Physisorption state via interaction with surfaces of not only magnetic but also diamagnetic materials. In a Physisorption state, the rotational motion of hydrogen molecules is modified due to the potential anisotropy. The Physisorption properties and interconversion rate of the ortho and para hydrogen have recently been investigated on well-defined surfaces, which allow detailed comparison with theory. Furthermore, relative abundance of the ortho and para hydrogen in astronomical circumstances has been reported in recent years, which often shows a value out of equilibrium with the environment temperature. Physisorption and ortho–para conversion on the surfaces of interstellar media are expected to enable deeper understanding of astronomical phenomena. In this article, we review recent progress of experimental and theoretical studies on the Physisorption and ortho–para conversion of molecular hydrogen and its relevance to the recent astronomical observation.
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electron stimulated defect formation in single walled carbon nanotubes studied by hydrogen thermal desorption spectroscopy
2009Co-Authors: Satoshi Arima, Sangkil Lee, Yutaka Mera, Shohei Ogura, Katsuyuki Fukutani, Yoshinori Sato, Kazuyuki Tohji, Koji MaedaAbstract:Abstract Defects in single-walled carbon nanotubes introduced by low-energy electron irradiation at 8 K were sensitively detected by cryogenic thermal desorption of hydrogen molecules H2 in the temperature range of 10–40 K. The thermal desorption spectrum was found to change significantly with sample annealing at temperatures as low as 40–70 K. Experimental results suggest that the H2 Physisorption sites responsible for the ‘defect’ peak at 28 K are interstitial channel space between nanotubes closely packed in bundles which becomes more easily accessible on damage. It is also suggested that the disordering provides groove sites for H2 Physisorption with smaller binding energy causing the damage-induced spectral component around 16 K, slightly lower than the desorption peak at 20 K that is observed in undamaged samples. The spectral change at 40–70 K could be interpreted by migration of adatoms at the low temperatures.
Toshiki Sugimoto - One of the best experts on this subject based on the ideXlab platform.
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effects of rotational symmetry breaking on Physisorption of ortho and para h 2 on ag 111
2014Co-Authors: Toshiki Sugimoto, Katsuyuki FukutaniAbstract:Quantum-state-selective thermal desorption of ${\mathrm{H}}_{2}$ weakly physisorbed on Ag(111) demonstrates significantly different desorption features between the nuclear-spin modifications. An energy shift due to the rotational-symmetry breaking induced by an anisotropic interaction affects not only the enthalpy but also the entropy of adsorption. The preexponential factor for desorption of the ortho-${\mathrm{H}}_{2}$ is about three times as large as that of the para-${\mathrm{H}}_{2}$. The entropy difference indicates a perpendicular orientation preference of anisotropic Physisorption potential, which also suggests the importance of partial hybridization interaction for weak Physisorption.
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Physisorption and ortho para conversion of molecular hydrogen on solid surfaces
2013Co-Authors: Katsuyuki Fukutani, Toshiki SugimotoAbstract:Abstract Molecular hydrogen exists in nuclear-spin isomers of ortho and para species according to the total nuclear spin. These species are correlated to the rotational states with even and odd rotational quantum numbers because of the symmetry of the total wavefunction with respect to the permutation of the two nuclei. Although interconversion between the ortho and para states is extremely slow in an isolated state, the conversion is promoted in a Physisorption state via interaction with surfaces of not only magnetic but also diamagnetic materials. In a Physisorption state, the rotational motion of hydrogen molecules is modified due to the potential anisotropy. The Physisorption properties and interconversion rate of the ortho and para hydrogen have recently been investigated on well-defined surfaces, which allow detailed comparison with theory. Furthermore, relative abundance of the ortho and para hydrogen in astronomical circumstances has been reported in recent years, which often shows a value out of equilibrium with the environment temperature. Physisorption and ortho–para conversion on the surfaces of interstellar media are expected to enable deeper understanding of astronomical phenomena. In this article, we review recent progress of experimental and theoretical studies on the Physisorption and ortho–para conversion of molecular hydrogen and its relevance to the recent astronomical observation.
John P Perdew - One of the best experts on this subject based on the ideXlab platform.
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van der waals correction to the Physisorption of graphene on metal surfaces
2019Co-Authors: Hong Tang, Jianmin Tao, Adrienn Ruzsinszky, John P PerdewAbstract:Adsorption is a scientifically and technologically important interfacial phenomenon, which however presents challenges to conventional density functional theory (DFT) due to the long-range van der Waals (vdW) interactions. We have developed a model of long-range vdW correction for Physisorption of graphene (G) on metals with the Lifshitz–Zaremba–Kohn second-order perturbation theory, by incorporating dipole- and quadrupole-surface interactions and screening effects. The Physisorption energies calculated by the model between graphene and eight metal surfaces (Al, Ni, Co, Pd, Pt, Cu, Ag, and Au), and the adsorption energies for the same G/metal structures from self-consistent DFT PBE (Perdew–Burke–Ernzerhof) calculations, are obtained in a range of distances between G and the metal surfaces. The sum of these two parts is the total adsorption energy as a function of the distance, from which the equilibrium distance and the binding energy are determined simultaneously. The results show high accuracy, with the...
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modeling the Physisorption of graphene on metals
2018Co-Authors: Jianmin Tao, Hong Tang, Abhirup Patra, Puskar Bhattarai, John P PerdewAbstract:Many processes of technological and fundamental importance occur on surfaces. Adsorption is one of these phenomena that has received the most attention. However, it presents a great challenge to conventional density functional theory. Starting with the Lifshitz-Zaremba-Kohn second-order perturbation theory, here we develop a long-range van der Waals (vdW) correction for Physisorption of graphene on metals. The model importantly includes quadrupole-surface interaction and screening effects. The results show that, when the vdW correction is combined with the Perdew-Burke-Enzerhof functional, it yields adsorption energies in good agreement with the random-phase approximation, significantly improving upon other vdW methods. We also find that, compared with the leading-order interaction, the higher-order quadrupole-surface correction accounts for about $25%$ of the total vdW correction, suggesting the importance of the higher-order term.
Kenneth S. W. Sing - One of the best experts on this subject based on the ideXlab platform.
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Physisorption of gases with special reference to the evaluation of surface area and pore size distribution iupac technical report
2015Co-Authors: Katsumi Kaneko, James P Olivier, F Rodriguezreinoso, Jean Rouquerol, Alexander V Neimark, Kenneth S. W. SingAbstract:Gas adsorption is an important tool for the characterisation of porous solids and fine powders. Major advances in recent years have made it necessary to update the 1985 IUPAC manual on Reporting Physisorption Data for Gas/Solid Systems. The aims of the present document are to clarify and standardise the presentation, nomenclature and methodology associated with the application of Physisorption for surface area assessment and pore size analysis and to draw attention to remaining problems in the interpretation of Physisorption data.
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classical interpretation of Physisorption isotherms at the gas solid interface
2012Co-Authors: Kenneth S. W. Sing, Françoise Rouquerol, Jean RouquerolAbstract:This chapter reviews the classical theories of gas Physisorption and discusses the application of empirical isotherm equations. The major part deals with adsorption of a pure gas. A few equations closely related to the Gibbs adsorption equation are first reviewed: Henry’s law, virial equations, Hill-de Boer equation. Then, attention is paid to (i) the Langmuir theory of localized monolayer adsorption, (ii) the Brunauer, Emmett and Teller theory of multimolecular adsorption and (iii) the Dubinin theory of micropore filling. A special section examines the stepwise adsorption isotherms due to 2D phase changes in the physisorbed layer. After that, the empirical isotherm equations proposed by Freundlich, Sips, Toth, Jensen–Seaton and also Langmuir (for multisite adsorption) are introduced. Finally, the adsorption of gas mixtures is considered and two useful models are introduced, namely, the extended Langmuir model and the Ideal Adsorbed Solution Theory.
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adsorption by clays pillared clays zeolites and aluminophosphates
2012Co-Authors: Jean Rouquerol, Philip L Llewellyn, Kenneth S. W. SingAbstract:This chapter examines the structure, morphology and Physisorption properties of clays, pillared clays, zeolites and phosphate-based molecular sieves. The influence of the layer structure of clays (either rigid or non-rigid) on the adsorption isotherms is analysed. The Physisorption properties of zeolites and phosphate-based molecular sieves are examined in the light of adsorption isotherms (of various gases, at various temperatures) and of calorimetric data. Several cases of re-organisation or sudden change in mobility of the adsorbate for a determined loading of the microporous structure are examined and interpreted. The final section refers to the many applications related to the adsorbent properties of these materials (e.g. gas separation, catalysis, detergency, dialysis, organic solvent dehydration, etc.)
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surface area and porosity
2008Co-Authors: Alexander V Neimark, Kenneth S. W. SingAbstract:The sections in this article are Introduction Physisorption of Gases Determination of Surface Area The BET Method The Standard Isotherm Concept Assessment of Porosity Capillary Condensation and the Kelvin Equation Adsorption Hysteresis Microporosity Micropore Analysis: Dubinin's Theory of Micropore Filling Micropore Analysis: Empirical Methods Other Methods for Micropore Pore Size Analysis Application of Density Functional Theory Adsorption at the Liquid–Solid Interface Adsorption from Solution Heat of Immersion Mercury Porosimetry General Conclusions Keywords: Physisorption; pore size; mercury porosimetry; heat of immersion
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reporting Physisorption data for gas solid systems
2008Co-Authors: Kenneth S. W. Sing, Jean Rouquerol, D H Everett, R A W Haul, L Moscou, Robert A Pierotti, T SiemieniewskaAbstract:The sections in this article are Introduction General Definitions and Terminology Methodology Methods for the Determination of Adsorption Isotherms Operational Definitions of Adsorption Experimental Procedures Outgassing the Adsorbent Determination of the Adsorption Isotherm Evaluation of Adsorption Data Presentation of Primary Data Classification of Adsorption Isotherms Adsorption Hysteresis Determination of Surface Area Application of the BET Method Empirical Procedures for Isotherm Analysis Assessment of Mesoporosity Properties of Porous Materials Application of the Kelvin Equation Computation of Mesopore Size Distribution Assessment of Microporosity Terminology Concept of Surface Area Assessment of Micropore Volume General Conclusions and Recommendations Keywords: Physisorption data; IUPAC; adsorption isotherms; surface area; BET isotherm
