NMR spectroscopy of dipole-coupled pairs of C-13 nuclei is employed to probe the molecular structure and dynamics of benzene molecules chemisorbed on a Pt/eta-Al2O3 catalyst. A modified Carr-Purcell sequence, which suppresses inhomogeneous broadening, permits good spectral resolution over a broad temperature range. A comparison between spectral data and computer simulations indicates more than one type of site for the chemisorbed molecules. The molecular structure appears to be indistinguishable from that in polycrystalline benzene but with a vastly different motional behavior.

Coal liquefaction kinetics have been studied at very short reaction times (less than 250 seconds) in order to emphasize the initial underlying physical and chemical processes involved. These studies were made possible by the use of a continuous flow stirred tank reactor (CSTR) which avoids the problems of slow heat up and cool down associated with the massive equipment required for running high-temperature and high-pressure liquefaction reactions. Preliminary physical (NMR and ESR) and chemical analytical results are presented on the coal liquids and reaction residues from Illinois No. 6 hnu bituminous and Wyodak Black Thunder subbituminous coals.ESR results showed that radical concentration in the solid residue changed during coal liquefaction. These changes were accompanied by changes in the NMR-derived aromaticity. The rate of decrease of organic-based radicals was different for Wyodak Black Thunder and Illinois No. 6 coals, perhaps indicating a different mechanism for the quenching of radicals in these bituminous and subbituminous coals. NMR spectra of the liquid products indicated that the initially produced material was relatively aromatic, and that subsequent products had lower aromatic content. This is consistent with secondary hydrogenation of the primary liquefaction products. Finally, the total oxygen contents of the coal residues decreased gradually during the first three minutes of coal liquefaction at 390-degrees-C. A corresponding decrease in the hydroxyl content of these residues was also noted.

Quantitative analysis of several standard materials is used to evaluate various techniques for analysis of 13C cross polarization magic angle spinning dipolar decoupling (CPMAS-DD)-NMR spectra. These results suggest that uncertainty in the kinetics of the initial cross-polarization process may lead to systematic errors in the fitting of CPMAS-DD-NMR data. Methods are suggested to minimize the effects of this potential source of error. These results indicate that 13C CPMAS-DD-NMR can give quantitatively reliable results.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGeometry and dynamics of benzene chemisorbed on a platinum/.eta.-alumina catalyst: a carbon-13 dipolar NMR studyM. Engelsberg, C. S. Yannoni, M. A. Jacintha, and Cecil DybowskiCite this: J. Am. Chem. Soc. 1992, 114, 21, 8319–8320Publication Date (Print):October 1, 1992Publication History Published online1 May 2002Published inissue 1 October 1992https://pubs.acs.org/doi/10.1021/ja00047a070https://doi.org/10.1021/ja00047a070research-articleACS PublicationsRequest reuse permissionsArticle Views57Altmetric-Citations12LEARN 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-Alertsclose Get e-Alerts