Quantum molecular sieving separability of D(2) from an H(2)-D(2) mixture was measured at 77 K for activated carbon fiber, carbon molecular sieve, zeolite and single wall carbon nanotube using a flow method. The amount of adsorbed D(2) was evidently larger than H(2) for all samples. The maximum adsorption ratio difference between D(2) and H(2) was 40% for zeolite (MS13X), yielding a selectivity for D(2) with respect to H(2) of 3.05.

We have Studied the hydrogenolysis of 2-(perfluorohexyl)ethane thiocyanate to 2-(perfluorohexyl)ethane thiol. it was discovered that perfluoroalkyl thiocyanates can be reduced to thiols and co-product hydrogen cyanide with molecular hydrogen in the presence of a carbon-supported palladium-tin catalyst. This result is Surprising since it is known that palladium and other groups 8 to 10 metal catalysts are poisoned by the product thiol, traces of hydrogen Sulfide byproduct, and the hydrogen cyanide co-product. For that reason, we characterized the catalyst to understand why it was so robust under conditions that Would normally poison such a catalyst.The effects of tin/palladium ratio, temperature, pressure, and recycling were Studied and correlated with catalyst characterization. The catalysts were characterized by chemisorption titrations, in situ X-Ray Diffraction (XRD), and Electron Spectroscopy for Chemical Analysis (ESCA). Chemisorption studies with hydrogen Sulfide show lack of adsorption at higher Sn/Pd ratios. Carbon monoxide chemisorption indicates an increase in adsorption with increasing palladium concentration. One form of palladium is transformed to a new phase at 140 degrees C by measurement of in situ variable temperature XRD. ESCA Studies of the catalysts show that the presence of tin concentration increases the surface palladium concentration. ESCA data also indicates that recycled catalysts show no palladium sulfide formation at the surface but palladium cyanide is present.

Over the past two decades, the photolytic reactions of dibenzyl ketones sorbed on zeolites have been investigated. The reported results are consistent with a supramolecular model that takes into account the physical and chemical nature of the structure of the zeolites and their effect on the reactive radical intermediates produced by photolysis of adsorbed molecules. The model incorporates various phenomena such as surface coverage, external and internal sorption, surface diffusion, radical sieving, and the resulting product distributions. This account reports direct evidence for the validation of the model through FT-IR spectroscopy and through a new method for "titrating" the binding sites via EPR spectroscopy. It is shown that it is possible to adjust and modulate the photolytic product distribution by varying the parameters of the system. The effects of co-adsorbed spectator molecules with different polarities, namely water, pyridine, and benzene, on the photolysis of o-methyldibenzyl ketone and dibenzyl ketone sorbed on MFI zeolites is examined. This study provides insights into a displacement mechanism caused by spectator molecules and further demonstrates how the product distribution of photolysis of sorbed ketones can be controlled. The kinetics of persistent radicals formed by photolysis of ketones sorbed on zeolites is directly monitored over time by EPR, providing a measure of the lifetime of these reactive organic intermediates. Finally, measurement of Langmuir isotherms was employed to provide classical evidence for the model.

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Sensitive and structurally specific methods for investigating silicalite external surface have been developed using electron paramagnetic resonance (EPR). The absorption of an EPR silent probe ortho-methyldibenzyl ketone (oMeDBK) (4 in Scheme 1) on the external surface of a series of monodisperse silicalite crystals was studied using an initially coadsorbed EPR active nitroxide probe. The displacement of the initially adsorbed nitroxide probe by coadsorbed oMeDBK shows that the adsorbate molecules first adsorb on stronger binding sites characterized by slow rotational motion of the probe (broad EPR lines) and after the stronger sites are saturated, the displaced EPR probe molecules adsorb on weaker binding sites characterized by fast rotational motion of the probe (narrow EPR lines). The transition point from slow to fast rotational motion provides a quantitative measurement of the stronger binding sites on the silicalite external surface area and the external surface area of silicalite crystals. The adsorption strength is molecular structure-dependent, and polar functional groups provide significant contribution to the binding strength. Sequential adsorption of 14N and 15N spin-labeled nitroxides shows the presence of the dynamic exchange between the adsorbates on the strong binding sites and those in solution or on the weak binding sites, while concurrent coadsorption of 14N and 15N spin-labeled nitroxides provides another sensitive means of studying the molecular structural dependence of the binding strength.

Investigation of the interaction of hydrogen with alkaline earth manganites (IV) AMnO3 (A=Ca, Sr, Ba), dispersed with 1at.% Pt, has revealed an unprecedented uptake of hydrogen by BaMnO3/Pt to the extent of ∼1.25mass% at moderate temperatures (190–260°C) and ambient pressure. Gravimetric sorption isotherms and mass spectrometric analysis of the desorption products indicate that approximately three hydrogen atoms per mol of BaMnO3/Pt is inserted reversibly. The nature of hydrogen in the insertion product, BaMnO3H3, is discussed. The work suggests the possibility of developing new hydrogen storage materials based on electropositive metal–transition metal–oxide systems.

Photolysis of ketones (1, 1-oMe, 2, 2-oMe, 3, and 4) adsorbed on ZSM-5 zeolites produces persistent carbon-centered radicals that can be readily observed by conventional steady-state EPR spectroscopy. The radicals are persistent for time periods of seconds to many hours depending on the supramolecular structure of the initial radical@zeolite complex and the diffusion and reaction dynamics of radicals produced by photolysis. The structures of the persistent radicals responsible for the observed EPR spectra are determined by a combination of alternate methods of generation of the same radical, by deuterium substitution, and by spectral simulation. A clear requirement for persistence is that the radicals produced by photolysis must either separate and diffuse from the external to the internal surface or be generated within the internal surface and separate and diffuse apart. The persistence of radicals located on the internal surface is the result of inhibition of radical-radical reactions. Radicals that are produced on the external surface and whose molecular structure prevents diffusion into the internal surface are transient because radical-radical reactions occur rapidly on the external surface. The reactions of the persistent radicals with oxygen and nitric oxide were directly studied in situ by EPR analysis. In the case of reaction with oxygen, persistent peroxy radicals are formed in high yield. The addition of nitric oxide scavenges persistent radicals and leads initially to a diamagnetic nitroso compound, which is transformed into a persistent nitroxide radical by further photolysis. The influence of variation of radical structure on transience/persistence is discussed and correlated with supramolecular structure and reactivity of the radicals and their parent ketones.

The large-scale commercial production of phosgene for the manufacture of pharmaceuticals, agrochemical, polyurethane and polycarbonates occurs over carbon catalysts and has been practiced worldwide for more than 70 years [1] . These catalysts are traditionally derived from conventional carbon materials, such as coconut shells. Although carbon as a catalyst is extremely selective, 100–1,000 parts per million of carbon tetrachloride are produced as a byproduct in this process. DuPont now has developed a new commercial catalyst that reduces the carbon tetrachloride level by an order of magnitude. The catalyst has been scaled up from the laboratory to commercial production without any problems. Lifetime of the new catalyst is also 5 to 10 times longer than that of the conventional coconut based carbons. This presentation will outline the experimental program, some characterization details and a possible mechanism for CCl 4 production. This is a rare example of how good science has resulted in the discovery of a new catalyst for an old process that eliminates an environmental issue with no investment.

Photochemical, magnetic resonance, adsorption isotherms, and surface area measurements have been integrated to investigate the surface coverage dependence of the supramolecular structure and dynamics of two isomeric ketones, oMeDBK (molecular cross section similar to that of o-xylene) and pMeDBK (molecular cross section similar to that of p-xylene),adsorbed an three forms of zeolites with the MFI structure:silicalite, ZSM-5, and; LZ-105. For each zeolite, the two isomeric ketones display striking qualitative differences in the experimental responses as a function of surface coverage. These differences are assigned to coverage-dependent changes in the supramolecular structural, dynamic, and binding characteristics of the adsorbed ketones and of the adsorbed reactive intermediates produced by photolysis of the ketones. In the case of pMeDBK, this ketone is adsorbed into the cages and channels of the internal surface. The external surface-consists of two,sites for the binding of oMeDBK: pores or "holes", and framework surface between the holes. The coverage dependence of the measured parameters for oMeDBK is consistent with a two-site model for adsorption on the external surface. Furthermore, a Langmuir expression for the adsorption isotherm of oMeDBK fits the experimental data for two binding sites. The entire array of data for oMeDBK is consistent with this model when the data are normalized for the different surface areas of the zeolites. Persistent radicals produced by the photolysis of oMeDBK and pMeDBK are observed directly by EPR analysis.

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTDual Templating of Macroporous Silicates with Zeolitic Microporous FrameworksBrian T. Holland, Lloyd Abrams, and Andreas SteinView Author Information Department of Chemistry, University of Minnesota Minneapolis, Minnesota, 55455 DuPont Central Research & Development Contribution No. 7910, Wilmington, Delaware, 19880 Cite this: J. Am. Chem. Soc. 1999, 121, 17, 4308–4309Publication Date (Web):April 16, 1999Publication History Received10 February 1999Published online16 April 1999Published inissue 1 May 1999https://pubs.acs.org/doi/10.1021/ja990425phttps://doi.org/10.1021/ja990425prapid-communicationACS PublicationsCopyright © 1999 American Chemical SocietyRequest reuse permissionsArticle Views3343Altmetric-Citations436LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Materials,Porous materials,Silica,Silicon,Zeolites Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTReversible Oxygenation of a Diphenylmethyl Radical Rendered Supramolecularly PersistentTakashi Hirano, Wei Li, Lloyd Abrams, Paul J. Krusic, M. Francesca Ottaviani, and Nicholas J. TurroView Author Information Department of Chemistry, Columbia University New York, New York 10027 E. I. duPont de Nemours and Co. Central Research Department Experimental Station, Wilmington, Delaware 19880 Contribution No. 7942 University of Urbino, Institute of Chemical Sciences Piazza Risorgimento 6, 61029 Urbino, Italy Cite this: J. Am. Chem. Soc. 1999, 121, 30, 7170–7171Publication Date (Web):July 16, 1999Publication History Received20 April 1999Revised16 June 1999Published online16 July 1999Published inissue 1 August 1999https://pubs.acs.org/doi/10.1021/ja9912628https://doi.org/10.1021/ja9912628rapid-communicationACS PublicationsCopyright © 1999 American Chemical SocietyRequest reuse permissionsArticle Views325Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Amorphous materials,Atmospheric chemistry,Electron paramagnetic resonance spectroscopy,Fluorescence,Saturation Get e-Alerts

Magnetic resonance, surface area measurements and computational techniques have been integrated to elucidate the supramolecular photochemistry of two isomeric ketones adsorbed on two MFI zeolites (silicalite and ZSM-5) and to demonstrate that common factors proportional to the available external surface area operate to determine the measured parameters in each case.

H-2 NMR, EPR, computational and product analyses of the photolysis of 2,4-diphenylpentan-3-one (DPP) adsorbed on MFI size/shape selective zeolites are consistent with supramolecular structural changes as a function of surface coverage that provide a novel method for the generation of persistent diffusing organic free radicals.

The kinetics of the hydrodechlorination of 1,1-dichlorotetrafluoroethane (CFC 114a) was studied on Pd(111), Pd(100), and a Pd foil at atmospheric pressure. The three products formed were CF3–CFH2(HFC 134a), CF3–CFClH (HCFC 124), and CF3–CH3(HFC 143a) with selectivities independent of conversion. The single crystals and foil (model catalysts) were studied in an apparatus that permitted the direct transfer of samples between a high pressure cell (1 atm) and an ultrahigh vacuum chamber. The reaction rates were measured in the temperature range of 350 to 470 K. The reaction is not sensitive to the structure of the catalyst, as indicated by the similar turnover rates for all catalysts tested. The reaction is inverse first order in the reaction product HCl on all samples. Sulfur adsorbed on the Pd surface depressed the rates of formation of 134a more strongly than the rates of 124 and 143a.

The kinetics (turnover rate, activation energy, reaction order) of catalytic hydrodechlorination of 1,1-dichlorotetrafluoroethane or CFC 114a (CF3-CFCl2) were determined on a ~ 0.5 cm2 palladium polycrystalline foil as a catalyst. The reaction rates were measured in the temperature range of 80-200°C at a total pressure of 770 Torr. Using a reaction cell that was connected to an ultrahigh vacuum surface characterization chamber the composition of the metal surface was monitored before and after reaction. The products formed in a parallel reaction network and the turnover rates at 150°C, 50 Torr CFC 114a, 100 Torr H2, and 0.1 Torr HCl were 2.1 s-1 for CF3-CFH2, 3.0× 10-1 s-1 for CF3-CFClH, and 6.4×10-2 s-1 for CF3-CH3. For the two most abundant products, the reaction order is 1 in CF3-CFCl2, 0.5 in H2 and -1 in the reaction product HCl. These results suggest that the rate determining step for the reaction is the associative chemisorption of CF3-CFCl2 on the palladium surface. The palladium surface was free of adsorbates after the reaction with the exception of sulfur impurity that may accumulate during reaction.

The kinetics (turnover rate, activation energy, reaction order) of catalytic hydrodechlorination of 1,1-dichlorotetrafluoroethane or CFC 114a (CF3-CFCl2) were determined on a ~ 0.5 cm2 palladium polycrystalline foil as a catalyst. The reaction rates were measured in the temperature range of 80-200°C at a total pressure of 770 Torr. Using a reaction cell that was connected to an ultrahigh vacuum surface characterization chamber the composition of the metal surface was monitored before and after reaction. The products formed in a parallel reaction network and the turnover rates at 150°C, 50 Torr CFC 114a, 100 Torr H2, and 0.1 Torr HCl were 2.1 s-1 for CF3-CFH2, 3.0× 10-1 s-1 for CF3-CFClH, and 6.4×10-2 s-1 for CF3-CH3. For the two most abundant products, the reaction order is 1 in CF3-CFCl2, 0.5 in H2 and -1 in the reaction product HCl. These results suggest that the rate determining step for the reaction is the associative chemisorption of CF3-CFCl2 on the palladium surface. The palladium surface was free of adsorbates after the reaction with the exception of sulfur impurity that may accumulate during reaction.