Faraday Discussions of The Chemical Society最新文献

{"title":"Ensemble and ligand effects in selective alkane hydrogenolysis catalysed on well characterised RhIr and RhFe bimetallic clusters inside NaY zeolite","authors":"M. Ichikawa, L. Rao, Tarō Itō, A. Fukuoka","doi":"10.1039/DC9898700321","DOIUrl":"https://doi.org/10.1039/DC9898700321","url":null,"abstract":"A series of metal/bimetal catalysts has been prepared from molecular carbonyl clusters such as Rh6–x Irx(CO)16(x= 0–6) and Rh4Fe2(CO)162– which were synthesized inside NaY zeolite supercages. Na Y-entrapped Rh6, Ir6, Rh4Ir2, Rh3Ir3 and Rh2Ir4 crystallites derived from the precursor carbonyl clusters have been well characterized by f.t.i.r., EXAFS, 129Xe n.m.r. and CO/H chemisorption on their metallic structures and electronic states. The results suggested that the reduced crystallites inside NaY zeolite consist of cluster ensembles < 10 A in size with controlled metal compositions. These ensembles are fairly stable through several cycles of oxidation, reduction and alkane hydrogenolysis. As the probing reactions, hydrogenolysis of n-butane and ethane, and benzene hydrogenation were conducted. There is a dramatic decrease of hydrogenolysis activity by four orders of magnitude across the series of clusters on increasing the number of Ir atoms in the active Rh ensembles, while a slight enhancement of activity is observed for benzene hydrogenation. The remarkable activity suppression of hydrogenolysis has been interpreted not simply in terms of the geometric Rh ensemble-size effect with a small amount of Ir atoms but of the different electronic states of the RhIr bimetallic clusters in decreasing the electron deficiency through the series clusters. This was demonstrated by the unusually large chemical shifts of n.m.r. signals of 129Xe adsorbed on NaY-Rh-rich clusters in reflecting the higher electron deficiency. For butane hydrogenolysis, the smaller Rh ensembles in bimetallic RhIr clusters gave the maximum selectivities towards the central C—C bond scission to give C2H6, higher than those on the Rh6 and Ir6 inside zeolites. In contrast, RhFe/NaY derived from [Rh4Fe2(CO)16]2–/NaY exhibited conversely a high selectivity towards terminal C—C bond scission to give CH4+ C3H8. The Fe promotion for the terminal C—C bond scission is suggested to be associated with the electronic ligand effect on the heteronuclear sites consisting of Rh–Fe3+ located on the internal zeolite cages.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"11 1","pages":"321-336"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72783642","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}

{"title":"Ellipsometric studies of polyaniline growth and redox cycling","authors":"R. Greef, M. Kalaji, L. Peter","doi":"10.1039/DC9898800277","DOIUrl":"https://doi.org/10.1039/DC9898800277","url":null,"abstract":"Ellipsometry has been used to characterise the growth of polyaniline films on platinum and gold electrodes by potential cycling. Analysis of the time evolution of the ellipsometric parameters allowed continuous monitoring of the growth process, and subsequent measurements of the changes in optical properties during oxidation and reduction of the PANI film were related to the electrochemical behaviour. Spectroscopic ellipsometry has been used to evaluate n and k values of the film for differing degrees of oxidation. Frequency-resolved transmission measurements have been used to show that the periodic electrical and optical responses of the polyaniline film are directly related.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"6 1","pages":"277-289"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80162912","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}

{"title":"Cation-oxygen geometry in polymer electrolytes: interpretation of EXAFS results","authors":"R. Latham, R. Linford, W. Schlindwein","doi":"10.1039/DC9898800103","DOIUrl":"https://doi.org/10.1039/DC9898800103","url":null,"abstract":"Two issues are of current interest in the field of ionically conducting polymers (polymer electrolytes): these are ion pairing and possible interference of the polymer-cation interaction by water. EXAFS was chosen as a suitable technique to probe local structure surrounding the cations. The systems studied were PEOn:ZnX2, where n= 6–15 and X = Cl, Br or I. They were chosen in order to ascertain the reliability of information pertaining to oxygen neighbours when the system under investigation contains heavy counterions. The results reveal, as expected, that the information about numbers of oxygen nearest neighbours is qualitative rather than quantitative, and firmer conclusions can be drawn for the lighter counterions. Cations and anions were found to be in close proximity, thus confirming ion pairing in PEO-zinc polymer electrolytes; this is in accord with recent observations of zinc diffusion.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"25 1","pages":"103-111"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81709812","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}

{"title":"Some aspects of catalyst characterisation and activity","authors":"P. Wells","doi":"10.1039/DC9898700001","DOIUrl":"https://doi.org/10.1039/DC9898700001","url":null,"abstract":"Knowledge of the connection between catalyst structure and catalytic activity is reviewed, examples being selected from reactions involving monophastic catalysts (oxides and sulphides, metal single crystals, zeolites) and multiphasic catalysts (especially supported metals). Contributions to our knowledge from surface science, conventional structure and characterisation studies, EXAFS spectroscopy, and in situ methods of catalyst evaluation are considered. Evidence that reversible displacements of atoms in the active phase may occur during catalytic conversions is noted, as is the importance of permanently retained hydrocarbonaceous species in the establishment of reproducible catalytic activity in metals. Throughout, the complementary nature and roles of structural information and mechanistic studies is emphasized.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"5 1","pages":"1-12"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80102106","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}

{"title":"Polyanilines: a novel class of conducting polymers","authors":"A. MacDiarmid, A. Epstein","doi":"10.1039/DC9898800317","DOIUrl":"https://doi.org/10.1039/DC9898800317","url":null,"abstract":"The polyanilines are a class of polymers the base form of which has the general formula [graphic omitted] containing y reduced and (1 –y) oxidized repeat groups. y can in principle be varied continuously from one, the completely reduced material, to zero to give the completely oxidized polymer. The emeraldine oxidation state (y= 0.5) consists of alternating reduced and oxidized groups. It can be protonated, i.e. doped, by aqueous acids with a concomitant increase in conductivity of almost 10 orders of magnitude (to a maximum conductivity of 101–102 S cm–1), forming a polysemiquinone radical cation such as [graphic omitted] which contains a delocalized half-filled broad polaron energy band. The polymer is readily solution-processed into films and fibres which can be mechanically aligned, the doped forms of which have a conductivity parallel to the direction of alignment significantly greater than that of non-aligned material. X-Ray studies show that the doped and undoped polymer exist in several different crystalline forms. A wide variety of derivatives can be synthesized by substitution on the ring or on the nitrogen.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"379 ","pages":"317-332"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91445724","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}

{"title":"Computational-chemical assessments of well characterised uniform catalysts","authors":"A. Cheetham, J. Gale, A. K. Nowak, B. Peterson, S. Pickett, John Meurig Thomas","doi":"10.1039/DC9898700079","DOIUrl":"https://doi.org/10.1039/DC9898700079","url":null,"abstract":"The use of computer-simulation procedures to model the behaviour of zeolites and other well characterised, uniform catalysts is discussed. We describe the prediction of the location of solute molecules and the estimation of heats of adsorption by molecular mechanics (MM) procedures. In addition, the use of Monte Carlo (MC) and molecular dynamics (MD) techniques to study sorbates at high loadings is considered, together with the calculation of diffusion coefficients by MD. The assessment of the stability of known and hypothetical zeolites by lattice-simulation procedures is described and we explore the extension of the method to pillared clays. The possibility of modelling a catalytic reaction mechanism by quantum-mechanical procedures is also examined.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"97 1","pages":"79-90"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81694641","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}

{"title":"Role of surface atomic arrangements of well defined phosphates in partial oxidation and oxidative dehydrogenation reactions","authors":"J. Védrine, J. Millet, J. Volta","doi":"10.1039/DC9898700207","DOIUrl":"https://doi.org/10.1039/DC9898700207","url":null,"abstract":"Various vanadium and iron phosphates have been synthesized and characterized physically before and after catalytic reaction has taken place. Vanadium phosphate was used for butane oxidation into maleic anhydride and iron phosphate for isobutyric acid dehydrogenation to methacrylic acid. Vanadium phosphate catalyst in its working state corresponds to a mixture of the pyrophosphate phase (VO)2P2O7 and a given VOPO4 phase (αII, β or δ). 31P MASNMR spectra showed that the most efficient catalysts contained VOPO4 entities in interaction with (VO)2P2O7, while an X-ray electronic radial distribution study showed that VOPO4 entities are present but not necessarily organized in sufficiently long-range order to be detected by classical X-ray diffraction. The iron phosphates Fe2P2O7, FePO4 and Fe7(PO4)6 were transformed under catalytic reaction into Fe7(PO4)6 and an unknown phase. The latter phase was tentatively assigned from Mossbauer spectroscopy to Fe6P6O23 with an Fe3+/Fe2+ ratio equal to two. The best catalysts including the industrial catalyst were those containing the Fe6P6O23 phase. A similarity has been found in the behaviour of vanadium and iron phosphates. The best catalysts correspond to those which exhibit short- or long-range order between the reduced pyrophosphate phase and a more oxidized form as VOPO4 or Fe6P6O23. It is suggested that the ease of transformation of two PO4 groups, at least locally, into one P2O7 group is the clue to obtaining an efficient catalyst. This is a case of topotactic transformation.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"55 1","pages":"207-213"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87379607","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}

{"title":"General Discussions of the Faraday Society/Faraday Discussions of the Chemical Society","authors":"R. Gillespie, S. Wasif","doi":"10.1039/DC989880X003","DOIUrl":"https://doi.org/10.1039/DC989880X003","url":null,"abstract":"","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"10 11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90663318","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}

{"title":"The structural background of charge-carrier motion in conducting polymers","authors":"G. Wegner, J. Rühe","doi":"10.1039/DC9898800333","DOIUrl":"https://doi.org/10.1039/DC9898800333","url":null,"abstract":"The conductivity of poly(3,4-cycloalkylpyrrole) perchlorates and the corresponding salts of poly(3,4-cycloalkylthiophene) can be analysed in terms of a mechanism assuming random hopping of charge carriers between localized states of adjacent chain segments of different chains. The conductivity can be expressed by σ=σ0 exp (–2αR) exp (–Ea/kt) where R is correlated to the size of the substituent at the pyrrole or thiophene units. Differences in conductivity between the polypyrrole and polythiophene systems can be quantitatively assessed and attributed to differences in the value of ∂Ea/∂R, this value being larger for polythiophene derivatives; Ea is an activation energy limited to the hopping process (phonon-assisted hopping). Systems with layered structures such as salts with long n-alkylsulphonate, -sulphate or -phosphonate counterions do not show a counterion-dependent conductivity. This is explained based on a structural model in which the closest packing distance remains unchanged when the length of the alkyl chain of the counterion changes. The same model explains the behaviour of poly(3-alkyl-pyrrole) salts as well. Polypyrrole salts of polymeric counterions show a behaviour similar to the materials with cycloaliphatic rings fused to the pyrrole units. This is quantitatively assessed taking the inhomogeneous distribution of counterions into account, which arises from the conformational disorder of the polymeric counterions.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"85 1","pages":"333-349"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90989494","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}

{"title":"A combined ellipsometric and in situ infrared (SNIFTIRS) study of poly(benzo-[c]-thiophene) films","authors":"P. Christensen, J. Kerr, S. Higgins, A. Hamnett","doi":"10.1039/DC9898800261","DOIUrl":"https://doi.org/10.1039/DC9898800261","url":null,"abstract":"Films of poly(benzo[c]thiophene)[poly(isothianaphthene)] have been grown from a solution of the monomer in acetonitrile by two methods. First, anionic polymerisation onto a platinum electrode in the presence of tetrafluoroborate affords a stable polymer (type I film). Secondly, oxidative polymerisation with Br2 as an electrochemically generated intermediate gives a rather different material (type II film). Films of type I are found by ellipsometry to be relatively dense, containing very little solvent in the neutral form. On switching from the neutral to the oxidised form, the film swells as solvent and counter anions are absorbed. Type II films are found to have a much more open form and estimates from ellipsometry and coulometry are consistent with a factor of four greater solvent content. Potential cycling of these films appears to have little effect on their thickness. The in situ i.r. measurements, carried out on a type I film, are consistent with absorption of solvent in the oxidised form, but the spectra are dominated by the development of a strong electronic absorption centred above 4000 cm–1 that shifts towards lower frequency at higher potentials. This electronic band is accompanied by the appearance of strong absorption bands between 1000 and 1400 cm–1 associated with the five-membered S-containing ring and correlating with the shift in electronic absorption maximum. The enhanced vibrational peaks are due to ‘amplitude-mode’ effects arising from the coupling of the quinonoid vibrations to the mobile charge defect. The evolution of the i.r. spectra with potential can then be associated with the changing character of the charge carriers.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"31 1","pages":"261-275"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86842989","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}