A magnetic linear dichroism MLD effect of up to 5% has been observed in the 2p 1/2 4d x-ray emission spectrum of Yb in Yb 3 Fe 5 O 12 . The spectral shape is well reproduced with an atomic multiplet calculation of the 4d to 2p decay. It is shown that the details of the spectral shapes are determined by the 4d4 f exchange interaction. While the integrated intensity of the MLD effect is zero, the magnitude of the effect is a direct measure of the 4 f magnetic moment of Yb. The technique is applicable to all rare-earth and transition-metal systems (probing the 3d magnetic moment). With respect to x-ray-absorption magnetic circular dichroism it possesses the advantage that (i) hard x rays are involved and (ii) no circular polarization is needed. Therefore all complications related to electron detection, soft x-ray experiments, and circular polarization disappear. Potential applications include the study of ~buried! magnetic systems in situ, at high pressures, varying (high) magnetic fields, and varying temperatures.
{"title":"Magnetic linear dichroism in x-ray emission spectroscopy: Yb in Yb3 Fe5 O12","authors":"F. Groot, M. Krisch, F. Sette, J. Vogel","doi":"10.1103/PHYSREVB.62.379","DOIUrl":"https://doi.org/10.1103/PHYSREVB.62.379","url":null,"abstract":"A magnetic linear dichroism MLD effect of up to 5% has been observed in the 2p 1/2 4d x-ray emission \u0000spectrum of Yb in Yb 3 Fe 5 O 12 . The spectral shape is well reproduced with an atomic multiplet calculation of \u0000the 4d to 2p decay. It is shown that the details of the spectral shapes are determined by the 4d4 f exchange \u0000interaction. While the integrated intensity of the MLD effect is zero, the magnitude of the effect is a direct \u0000measure of the 4 f magnetic moment of Yb. The technique is applicable to all rare-earth and transition-metal \u0000systems (probing the 3d magnetic moment). With respect to x-ray-absorption magnetic circular dichroism it \u0000possesses the advantage that (i) hard x rays are involved and (ii) no circular polarization is needed. Therefore \u0000all complications related to electron detection, soft x-ray experiments, and circular polarization disappear. \u0000Potential applications include the study of ~buried! magnetic systems in situ, at high pressures, varying (high) \u0000magnetic fields, and varying temperatures.","PeriodicalId":50986,"journal":{"name":"Catalysis Reviews-Science and Engineering","volume":"33 1","pages":""},"PeriodicalIF":10.9,"publicationDate":"2000-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76948700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-03-15DOI: 10.1103/PHYSREVB.61.7176
C. Wittkop, W. Schulke, F. Groot
Magnetic circular dichroism is observed for ferromagnetic EuO (T C 569 K) in the b2,15 fluorescence at incident photon energies resonant with the 2p 3/2 excitation. The dichroism is dominated by exchange interac-tion between the localized 4 f electrons and the final state 4d core hole. The spectral shapes obtained by atomic multiplet calculations for the 2p4d emission show good agreement with the experimental data.
{"title":"Magnetic circular dichroism in the 2p4d x-ray emission of EuO","authors":"C. Wittkop, W. Schulke, F. Groot","doi":"10.1103/PHYSREVB.61.7176","DOIUrl":"https://doi.org/10.1103/PHYSREVB.61.7176","url":null,"abstract":"Magnetic circular dichroism is observed for ferromagnetic EuO (T C 569 K) in the b2,15 fluorescence at \u0000incident photon energies resonant with the 2p 3/2 excitation. The dichroism is dominated by exchange interac-tion \u0000between the localized 4 f electrons and the final state 4d core hole. The spectral shapes obtained by atomic \u0000multiplet calculations for the 2p4d emission show good agreement with the experimental data.","PeriodicalId":50986,"journal":{"name":"Catalysis Reviews-Science and Engineering","volume":"19 1","pages":""},"PeriodicalIF":10.9,"publicationDate":"2000-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78799482","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-02-15DOI: 10.1103/PHYSREVB.61.5262
Z. Hu, H. Lips, M. Golden, J. Fink, G. Kaindl, F. Groot, S. Ebbinghaus, A. Reller
We report combined experimental and theoretical investigations of x-ray absorption at the $mathrm{Ru}{ensuremath{-}L}_{2,3}$ and O-K thresholds of the Ru(IV) compounds ${mathrm{RuO}}_{2}$ and ${mathrm{Sr}}_{2}{mathrm{RuO}}_{4}$ and of the Ru(V) compound ${mathrm{Sr}}_{4}{mathrm{Ru}}_{2}{mathrm{O}}_{9}.$ Significant differences in the intensity distribution of the ${t}_{2g}$-related and ${e}_{g}$-related peaks between the ${L}_{3}$ and the ${L}_{2}$ edges are found, due to the combined effects of $4d$ spin-orbit coupling and the interelectronic Coulomb interaction described by the Slater integrals. The observed spectral features can be well reproduced by crystal-field-multiplet calculations. With increasing the Ru valence from IV to V, the spectra are shifted by ensuremath{cong}1.5 eV to higher energy at the $mathrm{Ru}{ensuremath{-}L}_{2,3}$ edges and ensuremath{cong}1.0 eV to lower energy at the O-K edge, which is of the same order of magnitude as on going from the divalent to the trivalent late $3d$ transition-metal oxides.
{"title":"Multiplet effects in the Ru L2,3 x-ray-absorption spectra of Ru (IV) and Ru (V) compounds","authors":"Z. Hu, H. Lips, M. Golden, J. Fink, G. Kaindl, F. Groot, S. Ebbinghaus, A. Reller","doi":"10.1103/PHYSREVB.61.5262","DOIUrl":"https://doi.org/10.1103/PHYSREVB.61.5262","url":null,"abstract":"We report combined experimental and theoretical investigations of x-ray absorption at the $mathrm{Ru}{ensuremath{-}L}_{2,3}$ and O-K thresholds of the Ru(IV) compounds ${mathrm{RuO}}_{2}$ and ${mathrm{Sr}}_{2}{mathrm{RuO}}_{4}$ and of the Ru(V) compound ${mathrm{Sr}}_{4}{mathrm{Ru}}_{2}{mathrm{O}}_{9}.$ Significant differences in the intensity distribution of the ${t}_{2g}$-related and ${e}_{g}$-related peaks between the ${L}_{3}$ and the ${L}_{2}$ edges are found, due to the combined effects of $4d$ spin-orbit coupling and the interelectronic Coulomb interaction described by the Slater integrals. The observed spectral features can be well reproduced by crystal-field-multiplet calculations. With increasing the Ru valence from IV to V, the spectra are shifted by ensuremath{cong}1.5 eV to higher energy at the $mathrm{Ru}{ensuremath{-}L}_{2,3}$ edges and ensuremath{cong}1.0 eV to lower energy at the O-K edge, which is of the same order of magnitude as on going from the divalent to the trivalent late $3d$ transition-metal oxides.","PeriodicalId":50986,"journal":{"name":"Catalysis Reviews-Science and Engineering","volume":"31 1","pages":""},"PeriodicalIF":10.9,"publicationDate":"2000-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87986902","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-05-01DOI: 10.1080/01614949909353779
J. Bonardet, J. Fraissard, A. Gédéon, M. Springuel-Huet
Abstract Xenon is an inert gas with a large electronic environment that makes it sensitive to any interaction, even physical. In the case of 129Xe isotope (spin 1/2), the resulting electronic perturbation is directly transmitted to the nucleus and, therefore, affects the nuclear magnetic resonance chemical shift. In this review, we report exhaustively up to 1996 the many applications of this technique in both fundamental and applied research in the fields of microporous and mesoporous solids.
{"title":"Nuclear Magnetic Resonance of Physisorbed 129Xe Used as a Probe to Investigate Porous Solids","authors":"J. Bonardet, J. Fraissard, A. Gédéon, M. Springuel-Huet","doi":"10.1080/01614949909353779","DOIUrl":"https://doi.org/10.1080/01614949909353779","url":null,"abstract":"Abstract Xenon is an inert gas with a large electronic environment that makes it sensitive to any interaction, even physical. In the case of 129Xe isotope (spin 1/2), the resulting electronic perturbation is directly transmitted to the nucleus and, therefore, affects the nuclear magnetic resonance chemical shift. In this review, we report exhaustively up to 1996 the many applications of this technique in both fundamental and applied research in the fields of microporous and mesoporous solids.","PeriodicalId":50986,"journal":{"name":"Catalysis Reviews-Science and Engineering","volume":"18 4","pages":"115-225"},"PeriodicalIF":10.9,"publicationDate":"1999-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/01614949909353779","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72480692","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-05-01DOI: 10.1080/01614949909353780
G. Groppi, E. Tronconi, P. Forzatti
Abstract The various concepts of catalytic combustion for the production of energy are presented first. Then, the different configurations of catalytic combustion systems for gas turbine applications are described. The following aspects of the mathematical modeling of the catalyst section are addressed: (1) relevant physical and chemical phenomena; (2) comparison of mathematical models; (3) estimation of interphase transfer coefficients; (4) acquisition of kinetic data; (5) continuous versus discrete multichannel models. Selected examples of application of the models are then presented. Finally, the mathematical modeling of the homogeneous section is briefly discussed.
{"title":"Mathematical Models of Catalytic Combustors","authors":"G. Groppi, E. Tronconi, P. Forzatti","doi":"10.1080/01614949909353780","DOIUrl":"https://doi.org/10.1080/01614949909353780","url":null,"abstract":"Abstract The various concepts of catalytic combustion for the production of energy are presented first. Then, the different configurations of catalytic combustion systems for gas turbine applications are described. The following aspects of the mathematical modeling of the catalyst section are addressed: (1) relevant physical and chemical phenomena; (2) comparison of mathematical models; (3) estimation of interphase transfer coefficients; (4) acquisition of kinetic data; (5) continuous versus discrete multichannel models. Selected examples of application of the models are then presented. Finally, the mathematical modeling of the homogeneous section is briefly discussed.","PeriodicalId":50986,"journal":{"name":"Catalysis Reviews-Science and Engineering","volume":"3 1","pages":"227-254"},"PeriodicalIF":10.9,"publicationDate":"1999-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91066146","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-04-15DOI: 10.1103/PHYSREVB.59.9933
M. Finazzi, N. Brookes, F. Groot
We have investigated the behavior of the 2p3s3p, 2p3p3p, and 2p3s3s Auger lines of NiO, a model compound in the class of strongly correlated 3d systems, while varying the photon energy across the Ni L3 and L2 absorption edges. The experimental data are discussed in comparison with a theoretical model based on a charge-transfer multiplet approach. When the excitation energy is below the L3 resonance, we observe the 2p3p3p and 2p3s3p peaks at a constant binding energy. This behavior is typical of nonradiative resonant Raman scattering. If the photon energy is increased further, the 2p3p3p and 2p3s3p lines rapidly transform into constant kinetic energy features, showing a normal Auger behavior. The transition from Raman- to Auger-like behavior takes place for photon energies lower than the ones corresponding to excitations of the photoelectron into ligand-hole states. This might indicate the participation of inelastic processes in the recombination of the core hole involving energies much smaller than the NiO gap, or the possible presence of nonlocal effects. On the high photon energy side of the L3 edge, the constant kinetic energy of the 2p3p3p and 2p3s3p peaks is systematically larger than the one observed for an excitation well above the L2,3 edges. We attribute this behavior to the intervention of an intermediate state of 2p^5 3d^10 character, which has very little weight but is strongly enhanced at resonance.
{"title":"2p3s3p, 2p3p3p, and 2p3s3s resonant Auger spectroscopy from NiO","authors":"M. Finazzi, N. Brookes, F. Groot","doi":"10.1103/PHYSREVB.59.9933","DOIUrl":"https://doi.org/10.1103/PHYSREVB.59.9933","url":null,"abstract":"We have investigated the behavior of the 2p3s3p, 2p3p3p, and 2p3s3s Auger lines of NiO, a model \u0000compound in the class of strongly correlated 3d systems, while varying the photon energy across the Ni L3 and \u0000L2 absorption edges. The experimental data are discussed in comparison with a theoretical model based on a \u0000charge-transfer multiplet approach. When the excitation energy is below the L3 resonance, we observe the \u00002p3p3p and 2p3s3p peaks at a constant binding energy. This behavior is typical of nonradiative resonant \u0000Raman scattering. If the photon energy is increased further, the 2p3p3p and 2p3s3p lines rapidly transform \u0000into constant kinetic energy features, showing a normal Auger behavior. The transition from Raman- to \u0000Auger-like behavior takes place for photon energies lower than the ones corresponding to excitations of the \u0000photoelectron into ligand-hole states. This might indicate the participation of inelastic processes in the recombination \u0000of the core hole involving energies much smaller than the NiO gap, or the possible presence of \u0000nonlocal effects. On the high photon energy side of the L3 edge, the constant kinetic energy of the 2p3p3p \u0000and 2p3s3p peaks is systematically larger than the one observed for an excitation well above the L2,3 edges. \u0000We attribute this behavior to the intervention of an intermediate state of 2p^5 3d^10 character, which has very \u0000little weight but is strongly enhanced at resonance.","PeriodicalId":50986,"journal":{"name":"Catalysis Reviews-Science and Engineering","volume":"95 1","pages":""},"PeriodicalIF":10.9,"publicationDate":"1999-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80498271","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Composite Zeolite-Based Catalysts and Sorbents","authors":"P. Smirniotis, L. Davydov, E. Ruckenstein","doi":"10.1081/CR-100101949","DOIUrl":"https://doi.org/10.1081/CR-100101949","url":null,"abstract":"","PeriodicalId":50986,"journal":{"name":"Catalysis Reviews-Science and Engineering","volume":"39 1","pages":"43-113"},"PeriodicalIF":10.9,"publicationDate":"1999-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77442903","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Although technological practice should minimize environmental impact, this is not always economically feasible. During the past decade, for example, there has been increasing global concern over th...
{"title":"CO2 Reforming of CH4","authors":"M. Bradford, M. Vannice","doi":"10.1081/CR-100101948","DOIUrl":"https://doi.org/10.1081/CR-100101948","url":null,"abstract":"Although technological practice should minimize environmental impact, this is not always economically feasible. During the past decade, for example, there has been increasing global concern over th...","PeriodicalId":50986,"journal":{"name":"Catalysis Reviews-Science and Engineering","volume":"55 1","pages":"1-42"},"PeriodicalIF":10.9,"publicationDate":"1999-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85008780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A critical review of the kinetics and selectivity of the Fischer–Tropsch synthesis (FTS) is given. The focus is on reaction mechanisms and kinetics of the water–gas shift and Fischer–Tropsch (FT) reactions. New developments in the product selectivity as well as the overall kinetics are reviewed. It is concluded that the development of rate equations for the FTS should be based on realistic mechanistic schemes. Qualitatively, there is agreement that the product distribution is affected by the occurrence of secondary reactions (hydrogenation, isomerization, reinsertion, and hydrogenolysis). At high CO and H2O pressures, the most important secondary reaction is readsorption of olefins, resulting in initiation of chain growth processes. Secondary hydrogenation of α-olefins may occur and depends on the catalytic system and the process conditions. The rates of the secondary reactions increase exponentially with chain length. Much controversy exists about whether these chain-length dependencies stem from differe...
{"title":"Kinetics and Selectivity of the Fischer–Tropsch Synthesis: A Literature Review","authors":"G. V. D. Laan, A. Beenackers","doi":"10.1081/CR-100101170","DOIUrl":"https://doi.org/10.1081/CR-100101170","url":null,"abstract":"A critical review of the kinetics and selectivity of the Fischer–Tropsch synthesis (FTS) is given. The focus is on reaction mechanisms and kinetics of the water–gas shift and Fischer–Tropsch (FT) reactions. New developments in the product selectivity as well as the overall kinetics are reviewed. It is concluded that the development of rate equations for the FTS should be based on realistic mechanistic schemes. Qualitatively, there is agreement that the product distribution is affected by the occurrence of secondary reactions (hydrogenation, isomerization, reinsertion, and hydrogenolysis). At high CO and H2O pressures, the most important secondary reaction is readsorption of olefins, resulting in initiation of chain growth processes. Secondary hydrogenation of α-olefins may occur and depends on the catalytic system and the process conditions. The rates of the secondary reactions increase exponentially with chain length. Much controversy exists about whether these chain-length dependencies stem from differe...","PeriodicalId":50986,"journal":{"name":"Catalysis Reviews-Science and Engineering","volume":"3 1","pages":"255-318"},"PeriodicalIF":10.9,"publicationDate":"1999-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73246942","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Silica-based Ziegler–Natta catalysts are important industrially in the manufacture of polyethylene and polypropylene. They are scientifically very interesting because of the complex effects of porous silica on catalyst performance. This patent review explains how silica–based Ziegler–Natta catalysts are related to Phillips chromium–silica catalysts and explores their value for the gas phase and slurry processes for the manufacture of polyolefins. The subcategories dealt with are the following: magnesium–titanium–silica catalysts, which are valuable for high-density polyethylene, for the ethylene copolymers called linear low-density polyethylene;and ethylene–propylene rubber, and for isotactic polypropylene; vanadium–silica catalysts, which are useful in the polymerization and copolymerization of ethylene; and vanadium plus titanium–silica catalysts which often exhibit reactivity synergism. Dual-site and multisite catalysts are also reviewed.
{"title":"Silica-Based Ziegler–Natta Catalysts: A Patent Review","authors":"T. J. Pullukat, R. Hoff","doi":"10.1081/CR-100101172","DOIUrl":"https://doi.org/10.1081/CR-100101172","url":null,"abstract":"Silica-based Ziegler–Natta catalysts are important industrially in the manufacture of polyethylene and polypropylene. They are scientifically very interesting because of the complex effects of porous silica on catalyst performance. This patent review explains how silica–based Ziegler–Natta catalysts are related to Phillips chromium–silica catalysts and explores their value for the gas phase and slurry processes for the manufacture of polyolefins. The subcategories dealt with are the following: magnesium–titanium–silica catalysts, which are valuable for high-density polyethylene, for the ethylene copolymers called linear low-density polyethylene;and ethylene–propylene rubber, and for isotactic polypropylene; vanadium–silica catalysts, which are useful in the polymerization and copolymerization of ethylene; and vanadium plus titanium–silica catalysts which often exhibit reactivity synergism. Dual-site and multisite catalysts are also reviewed.","PeriodicalId":50986,"journal":{"name":"Catalysis Reviews-Science and Engineering","volume":"84 1","pages":"389-428"},"PeriodicalIF":10.9,"publicationDate":"1999-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80797181","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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