Transference numbers determined by the classical Hittorf method for liquid polymer electrolytes (solutions of NaSCN etc. in copolymers of ethylene and propylene oxide) yield consistently low values of t+(ca. 0.05). This points to a model in which cations are immobilised by interaction with the polymeric solvent and anions are the principal charge carriers, seemingly at variance with the successful operation of prototype lithium batteries. This paradox is resolved by postulating the ‘transport’ of Li+ ions from anode to cathode via the diffusion of ion pairs down a concentration gradient. A similar mechanism would also explain the higher values of t+(ca. 0.5) determined by the ‘steady-state current’ method and reported elsewhere in the literature.
{"title":"Ion transport in polymer electrolytes","authors":"G. G. Cameron, M. Ingram, J. Harvie","doi":"10.1039/DC9898800055","DOIUrl":"https://doi.org/10.1039/DC9898800055","url":null,"abstract":"Transference numbers determined by the classical Hittorf method for liquid polymer electrolytes (solutions of NaSCN etc. in copolymers of ethylene and propylene oxide) yield consistently low values of t+(ca. 0.05). This points to a model in which cations are immobilised by interaction with the polymeric solvent and anions are the principal charge carriers, seemingly at variance with the successful operation of prototype lithium batteries. This paradox is resolved by postulating the ‘transport’ of Li+ ions from anode to cathode via the diffusion of ion pairs down a concentration gradient. A similar mechanism would also explain the higher values of t+(ca. 0.5) determined by the ‘steady-state current’ method and reported elsewhere in the literature.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"35 1","pages":"55-63"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82698411","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A principal goal of the field of conducting polymers is to strive for advances in materials quality that will enable the exploration of the intrinsic electrical properties. In this context, we summarize the requirements for achieving high performance conducting polymers with electrical conductivities greater than that of copper. To avoid localization onto one-dimensioal polymer chains (with bandwidth 4t0), interchain charge transfer (t3d) is required. For crystalline materials in which the chains have precise phase order, the mean distance along the chain between defects must be L/acrystalline≫t0/t3d. In the case where there is good chain extension and good chain alignment, but when that alignment is nematic (i.e. with random interchain phase along the chain), the criterion is more severe: L/anematic≫(t0/t3d)2. When the appropriate inequality is satisfied the transport is that of an anisotropic three-dimensional metal, and the conductivity will increase in proportion to the mean distance between chain interruptions, cross-links, sp3 defects etc. If the mean defect scattering time, τdef=(L/vF), becomes sufficiently long that phonon scattering limits the mean free path, then the conductivity takes on a metallic temperature dependence, and the system is in the clean and intrinsic transport limit.
{"title":"Charge transfer in conducting polymers. Striving toward intrinsic properties","authors":"A. Heeger","doi":"10.1039/DC9898800203","DOIUrl":"https://doi.org/10.1039/DC9898800203","url":null,"abstract":"A principal goal of the field of conducting polymers is to strive for advances in materials quality that will enable the exploration of the intrinsic electrical properties. In this context, we summarize the requirements for achieving high performance conducting polymers with electrical conductivities greater than that of copper. To avoid localization onto one-dimensioal polymer chains (with bandwidth 4t0), interchain charge transfer (t3d) is required. For crystalline materials in which the chains have precise phase order, the mean distance along the chain between defects must be L/acrystalline≫t0/t3d. In the case where there is good chain extension and good chain alignment, but when that alignment is nematic (i.e. with random interchain phase along the chain), the criterion is more severe: L/anematic≫(t0/t3d)2. When the appropriate inequality is satisfied the transport is that of an anisotropic three-dimensional metal, and the conductivity will increase in proportion to the mean distance between chain interruptions, cross-links, sp3 defects etc. If the mean defect scattering time, τdef=(L/vF), becomes sufficiently long that phonon scattering limits the mean free path, then the conductivity takes on a metallic temperature dependence, and the system is in the clean and intrinsic transport limit.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"17 1","pages":"203-211"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88648010","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Physicochemical and catalytic properties of heteropolyacids of the series H3 +nPVnMo12–nO40(n= 0–3), both pure and supported on the potassium salt K3PMo12O40, have been investigated. Thin acid coats formed on such a support display modified properties and enhanced thermal stability. In particular, it is postulated that the change in the acidic properties of the supported acids is a consequence of their modified hydration ability resulting from the epitaxial relationship with the support. Results of catalytic experiments for the oxidation of acrolein, methanol and alkanes are presented and compared for both series of the catalysts. Possible mechanisms of all these processes are proposed on the basis of experimental data and quantum-chemical calculations.
{"title":"Acid–base and oxidation catalysis on heteropolysalts with surface acid layers","authors":"K. Bruckman, J. Haber, E. Serwicka","doi":"10.1039/DC9898700173","DOIUrl":"https://doi.org/10.1039/DC9898700173","url":null,"abstract":"Physicochemical and catalytic properties of heteropolyacids of the series H3 +nPVnMo12–nO40(n= 0–3), both pure and supported on the potassium salt K3PMo12O40, have been investigated. Thin acid coats formed on such a support display modified properties and enhanced thermal stability. In particular, it is postulated that the change in the acidic properties of the supported acids is a consequence of their modified hydration ability resulting from the epitaxial relationship with the support. Results of catalytic experiments for the oxidation of acrolein, methanol and alkanes are presented and compared for both series of the catalysts. Possible mechanisms of all these processes are proposed on the basis of experimental data and quantum-chemical calculations.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"45 1","pages":"173-187"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86868119","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ionic resistivities and counterion diffusion coefficients for polypyrrole, poly-[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium](poly-MPMP+) and pyrrolex-[Ru(2,2′-bipyridine)2(3-(pyrrol-1-ylmethyl) pyridine)Cl]+ copolymer films have been obtained by chronoamperometry using the single-pore model. For poly-MPMP+ both the electronic resistivity and the ionic resistivity can be simultaneously determined. Finite-difference simulations have been used to confirm the validity of the equations used and to extend the applicability of the model.Counterion diffusion coefficients in polypyrrole and poly-MPMP+ have also been determined by rotating-disc voltammetry and d.c. conductivity measurements. Where possible the results have been confirmed by the use of two independent methods. Diffusion coefficients for I–, Cl–, ClO4– and Fe(CN)64– in the above polymers in water and/or acetonitrile are compared and discussed. It is concluded that: (a) polypyrrole and poly-MPMP+ are solvated and swollen to a much greater extent in water than in acetonitrile, (b) permanent cationic sites increase the permeability of polypyrrole in water but not in acetonitrile and (c) the permeability of polypyrrole in acetonitrile can be increased by the incorporation of bulky metal complexes.
{"title":"Ion transport in pyrrole-based polymer films","authors":"Huanyu Mao, J. Ochmańska, C. Paulse, P. Pickup","doi":"10.1039/DC9898800165","DOIUrl":"https://doi.org/10.1039/DC9898800165","url":null,"abstract":"Ionic resistivities and counterion diffusion coefficients for polypyrrole, poly-[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium](poly-MPMP+) and pyrrolex-[Ru(2,2′-bipyridine)2(3-(pyrrol-1-ylmethyl) pyridine)Cl]+ copolymer films have been obtained by chronoamperometry using the single-pore model. For poly-MPMP+ both the electronic resistivity and the ionic resistivity can be simultaneously determined. Finite-difference simulations have been used to confirm the validity of the equations used and to extend the applicability of the model.Counterion diffusion coefficients in polypyrrole and poly-MPMP+ have also been determined by rotating-disc voltammetry and d.c. conductivity measurements. Where possible the results have been confirmed by the use of two independent methods. Diffusion coefficients for I–, Cl–, ClO4– and Fe(CN)64– in the above polymers in water and/or acetonitrile are compared and discussed. It is concluded that: (a) polypyrrole and poly-MPMP+ are solvated and swollen to a much greater extent in water than in acetonitrile, (b) permanent cationic sites increase the permeability of polypyrrole in water but not in acetonitrile and (c) the permeability of polypyrrole in acetonitrile can be increased by the incorporation of bulky metal complexes.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"48 1","pages":"165-176"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85077259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Analytical expressions quantifying the transport and kinetics in polymer-modified electrodes containing a homogeneous distribution of spherical microparticulate catalysts are presented. In particular the dependence of the flux on the number of catalytic particles per unit volume, the layer thickness, the substrate and mediator concentrations, the particle radius and the electrode potential are outlined for the situation of conducting polymer catalyst and ionomer–mediator–catalyst composites. A strategy for optimising the electrocatalytic behaviour of these multicomponent microheterogeneous systems is also outlined.
{"title":"Transport and kinetics in multicomponent chemically modified electrodes","authors":"M. Lyons, D. McCormack, Orla Smyth, P. Bartlett","doi":"10.1039/DC9898800139","DOIUrl":"https://doi.org/10.1039/DC9898800139","url":null,"abstract":"Analytical expressions quantifying the transport and kinetics in polymer-modified electrodes containing a homogeneous distribution of spherical microparticulate catalysts are presented. In particular the dependence of the flux on the number of catalytic particles per unit volume, the layer thickness, the substrate and mediator concentrations, the particle radius and the electrode potential are outlined for the situation of conducting polymer catalyst and ionomer–mediator–catalyst composites. A strategy for optimising the electrocatalytic behaviour of these multicomponent microheterogeneous systems is also outlined.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"10 1","pages":"139-149"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84157700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cu–Zn hydroxycarbonates have been studied as precursors of Cu–ZnO catalysts, with particular reference to the effect on catalyst activity of ageing the precursor prior to decomposition and reduction. The precursor obtained by precipitation from mixed nitrate solution (Cu/Zn molar ratio 2:1) at 333 K and pH 7.0 consisted of zincian malachite (Cu/Zn ≈ 85:15) and aurichalcite. The precursor was aged in the mother liquor at 333 K for various times. Characterisation by XRD, i.r., DTA, electron microscopy, EDAX and XPS showed that ageing led to loss of the aurichalcite and production of a more finely divided copper-enriched (Cu/Zn = 2:1) malachite phase. The unaged precursor yielded a catalyst of low activity for both methanol synthesis (studied at 50 bar and at 1 bar) and the reverse water-gas shift reaction. The aged precursor gave catalysts of much higher activity for both reactions. Increased ageing did not change the selectivity ratio for methanol synthesis vs. reverse shift in the CO2+ H2 reaction at normal pressure.
{"title":"Copper–zinc oxide catalysts. Activity in relation to precursor structure and morphology","authors":"D. Waller, D. Stirling, F. Stone, M. S. Spencer","doi":"10.1039/DC9898700107","DOIUrl":"https://doi.org/10.1039/DC9898700107","url":null,"abstract":"Cu–Zn hydroxycarbonates have been studied as precursors of Cu–ZnO catalysts, with particular reference to the effect on catalyst activity of ageing the precursor prior to decomposition and reduction. The precursor obtained by precipitation from mixed nitrate solution (Cu/Zn molar ratio 2:1) at 333 K and pH 7.0 consisted of zincian malachite (Cu/Zn ≈ 85:15) and aurichalcite. The precursor was aged in the mother liquor at 333 K for various times. Characterisation by XRD, i.r., DTA, electron microscopy, EDAX and XPS showed that ageing led to loss of the aurichalcite and production of a more finely divided copper-enriched (Cu/Zn = 2:1) malachite phase. The unaged precursor yielded a catalyst of low activity for both methanol synthesis (studied at 50 bar and at 1 bar) and the reverse water-gas shift reaction. The aged precursor gave catalysts of much higher activity for both reactions. Increased ageing did not change the selectivity ratio for methanol synthesis vs. reverse shift in the CO2+ H2 reaction at normal pressure.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"45 1","pages":"107-120"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89602593","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Centi, F. Trifiró, G. Busca, J. Ebner, J. Gleaves
TEM, EXAFS, FTIR, temporal analysis of products (TAP), stopped-flow desorption (SFD) and catalytic measurements of (VO)2P2O7 are reported. The reduced interaction between (020) planes of (VO)2P2O7 in samples prepared in an organic medium induces a charge localization on the V atoms of the coupled trans-vanadyl present in this plane, enhancing their catalytic reactivity in butane oxidation. Contiguous surface Bronsted sites (P—OH) also participate in the mechanism of selective oxidation. C-containing residues are present in relevant amount on the surface during catalytic experiments and give rise to a specific fouling of the active sites, but their possible role as co-catalysts in the transfer mechanisms of single activated species is also discussed.
{"title":"Nature of active species of (VO)2P2O7 for selective oxidation of n-butane to maleic anhydride","authors":"G. Centi, F. Trifiró, G. Busca, J. Ebner, J. Gleaves","doi":"10.1039/DC9898700215","DOIUrl":"https://doi.org/10.1039/DC9898700215","url":null,"abstract":"TEM, EXAFS, FTIR, temporal analysis of products (TAP), stopped-flow desorption (SFD) and catalytic measurements of (VO)2P2O7 are reported. The reduced interaction between (020) planes of (VO)2P2O7 in samples prepared in an organic medium induces a charge localization on the V atoms of the coupled trans-vanadyl present in this plane, enhancing their catalytic reactivity in butane oxidation. Contiguous surface Bronsted sites (P—OH) also participate in the mechanism of selective oxidation. C-containing residues are present in relevant amount on the surface during catalytic experiments and give rise to a specific fouling of the active sites, but their possible role as co-catalysts in the transfer mechanisms of single activated species is also discussed.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"50 1","pages":"215-225"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80889211","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Heteropoly oxometallates have been employed in the heterogeneous catalysis of the conversion of methanol to hydrocarbons and the partial oxidation of methane. In the former process methanol is first protonated at Bronsted-acid sites, but at higher temperatures the heteropoly anions are partially methylated subsequent to scission of the C—O bonds in protonated methanol. With silica-supported 12-molybdophosphoric acid the exchange of the protons by cations effectively poisons the catalyst for the conversion of methane. Introduction of a chloro-additive to the feedstream in the latter process produces changes in the conversion and selectivity which are markedly different for the molybdenum- and tungsten-containing catalysts. With the former the conversion of methane is increased while the selectivity to partial oxidation products is decreased. With the latter the former comments are also applicable but selectivities to methyl chloride reach as high as 90 mol %. The results from cation exchange and the addition of a chloro-additive are interpreted and a mechanism with common features is proposed for the methanol and methane conversion processes.
{"title":"Mechanistic relationships in the activation of methane and the conversion of methanol on heteropoly oxometallates","authors":"Shamsuddin Ahmed, S. Kasztelan, J. Moffat","doi":"10.1039/DC9898700023","DOIUrl":"https://doi.org/10.1039/DC9898700023","url":null,"abstract":"Heteropoly oxometallates have been employed in the heterogeneous catalysis of the conversion of methanol to hydrocarbons and the partial oxidation of methane. In the former process methanol is first protonated at Bronsted-acid sites, but at higher temperatures the heteropoly anions are partially methylated subsequent to scission of the C—O bonds in protonated methanol. With silica-supported 12-molybdophosphoric acid the exchange of the protons by cations effectively poisons the catalyst for the conversion of methane. Introduction of a chloro-additive to the feedstream in the latter process produces changes in the conversion and selectivity which are markedly different for the molybdenum- and tungsten-containing catalysts. With the former the conversion of methane is increased while the selectivity to partial oxidation products is decreased. With the latter the former comments are also applicable but selectivities to methyl chloride reach as high as 90 mol %. The results from cation exchange and the addition of a chloro-additive are interpreted and a mechanism with common features is proposed for the methanol and methane conversion processes.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"166 1","pages":"23-32"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77291950","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Pinnavaia, M. Rameswaran, E. Dimotakis, E. Giannelis, E. Rightor
Acidic pillared clays, e.g. alumina pillared montmorillonite (APM), and basic layered double hydroxides, e.g. hydrotalcite (HT), provide well defined surface environments for dispersing metal-cluster carbonyl complexes. In the present work, FTIR spectroscopic studies have been used to elucidate the surface organometallic chemistry of Ru3(CO)12 on APM and HT. For APM as the support, cluster binding occurs initially by protonation to form H Ru3(CO)12+ cations on the intracrystalline gallery surfaces of the clay. Further reaction results in the grafting of mononuclear sites of the type [Ru(CO)x(OAl)2]n(x= 2, 3) to the pillar surfaces. The reaction of Ru3(CO)12 with HT affords chemisorbed H Ru3(CO)11– anions which can be tranformed to surface-bound [Ru(CO)x(OM)2]n(M = Al, Mg) complexes analogous to the grafted species on APM. The reduction of the grafted complex on both supports results in active ruthenium catalysts for CO hydrogenation. Ru-APM exhibits very high selectivity for isomerized hydrocarbons (branched alkanes and internal alkenes). The isomerized products arise from the unique texture and bifunctional nature of Ru-APM; the clay-embedded ruthenium catalyses Fischer–Tropsch chain propagation, and the intracrystalline Bronsted acidity of the clay host catalyses alkene rearrangements through carbenium-ion mechanisms. In contrast, the Ru-HT system gives very different product distributions containing a high fraction of oxygenates, specifically methanol and lesser amounts of C2–C4 alcohols. The high alcohol selectivity, which is atypical for CO hydrogenation over Ru, is ascribed in part to the inhibition of CO dissociation on the metal particles by decoraments provided by the highly basic support.
{"title":"Carbon monoxide hydrogenation selectivity of catalysts derived from ruthenium clusters on acidic pillared clay and basic layered double-hydroxide supports","authors":"T. Pinnavaia, M. Rameswaran, E. Dimotakis, E. Giannelis, E. Rightor","doi":"10.1039/DC9898700227","DOIUrl":"https://doi.org/10.1039/DC9898700227","url":null,"abstract":"Acidic pillared clays, e.g. alumina pillared montmorillonite (APM), and basic layered double hydroxides, e.g. hydrotalcite (HT), provide well defined surface environments for dispersing metal-cluster carbonyl complexes. In the present work, FTIR spectroscopic studies have been used to elucidate the surface organometallic chemistry of Ru3(CO)12 on APM and HT. For APM as the support, cluster binding occurs initially by protonation to form H Ru3(CO)12+ cations on the intracrystalline gallery surfaces of the clay. Further reaction results in the grafting of mononuclear sites of the type [Ru(CO)x(OAl)2]n(x= 2, 3) to the pillar surfaces. The reaction of Ru3(CO)12 with HT affords chemisorbed H Ru3(CO)11– anions which can be tranformed to surface-bound [Ru(CO)x(OM)2]n(M = Al, Mg) complexes analogous to the grafted species on APM. The reduction of the grafted complex on both supports results in active ruthenium catalysts for CO hydrogenation. Ru-APM exhibits very high selectivity for isomerized hydrocarbons (branched alkanes and internal alkenes). The isomerized products arise from the unique texture and bifunctional nature of Ru-APM; the clay-embedded ruthenium catalyses Fischer–Tropsch chain propagation, and the intracrystalline Bronsted acidity of the clay host catalyses alkene rearrangements through carbenium-ion mechanisms. In contrast, the Ru-HT system gives very different product distributions containing a high fraction of oxygenates, specifically methanol and lesser amounts of C2–C4 alcohols. The high alcohol selectivity, which is atypical for CO hydrogenation over Ru, is ascribed in part to the inhibition of CO dissociation on the metal particles by decoraments provided by the highly basic support.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"167 1","pages":"227-237"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87939578","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Results of extended Huckel calculations show that coordination of CO to Group VIII transition-metal surfaces depends on a subtle balance of the interaction with the CO 5σ orbital, that tends to direct the CO molecule to the atop position and the CO 2 π* orbital, that directs the molecule to higher coordination sites. In the atop position, the changes in bonding to different surfaces of the same metal can be mainly attributed to differences in the interaction with the CO 5σ molecular orbital. The favoured dissociation path is such that carbon and oxygen atoms end in high coordination sites, sharing as few surface metal atoms as possible. The CO bond is activated by the metal atoms that are crossed upon dissociation.
{"title":"Reactivity of CO on stepped and non-stepped surfaces of transition metals","authors":"D. A. Koster, A. Jansen, V. Santen, J. Geerlings","doi":"10.1039/DC9898700263","DOIUrl":"https://doi.org/10.1039/DC9898700263","url":null,"abstract":"Results of extended Huckel calculations show that coordination of CO to Group VIII transition-metal surfaces depends on a subtle balance of the interaction with the CO 5σ orbital, that tends to direct the CO molecule to the atop position and the CO 2 π* orbital, that directs the molecule to higher coordination sites. In the atop position, the changes in bonding to different surfaces of the same metal can be mainly attributed to differences in the interaction with the CO 5σ molecular orbital. The favoured dissociation path is such that carbon and oxygen atoms end in high coordination sites, sharing as few surface metal atoms as possible. The CO bond is activated by the metal atoms that are crossed upon dissociation.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"62 1","pages":"263-273"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77185736","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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