Promotion of a Rh/SiO/sub 2/ catalyst with lanthana results in a partial coverage of the supported Rh crystallites with LaO/sub x/ islands. These moieties reduce the capacity of Rh to adsorb CO but have little effect on the chemisorption of H/sub 2/ because of spillover of H atoms from the exposed Rh sites onto the surface of the LaO/sub x/ islands. At elevated temperatures, the LaO/sub x/ islands promote the dissociation of CO. It is proposed that this process occurs preferentially at Rh sites located along the perimeter of the LaO/sub x/ islands. Support for this interpretation is provided by infrared spectra of CO adsorbed on lanthana-promoted Rh/SiO/sub 2/. 40 references.

LSMO

Abstract Using attenuated total‐reflectance infrared spectroscopy (ATR/FTIR), the concentration of deuterated polybutadiene near the surface of a flat zinc selenide crystal was followed as it was replaced by ordinary polybutadiene by flow and diffusion. Experiments were performed in the melt, both below (M ∼ 1,500) and above (M ∼ 15,000) the entanglement threshold. The decay profiles agree well with a finite‐element simulation of the system. In contrast to previous investigations of C 16 's, the decay profiles of both unentangled and entangled polybutadienes are consistent with a uniform diffusivity in the near‐wall region.

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A single-element rotating-polarizer ellipsometer (psi-meter) was used for in situ characterization of the thermodynamic and kinetic behavior of poly-(methyl methacrylate), PMMA, thin films (1.2 μm) in solvent/nonsolvent binary mixtures of methyl ethyl ketone/isopropanol (MEK/IPA) and methyl isobutyl ketone/methanol (MIBK/MeOH). Thermodynamic effects were inferred from equilibrium behavior by the degree of swelling and polymer-solvent solubility. A sharp transition between complete solubility and almost total insolubility was observed in a narrow concentration range near 50:50 (by volume) solvent/nonsolvent for both MEK/IPA and MIBK/MeOH. In the insoluble regime, the polymer was found to swell up to three times the initial thickness. At 50:50 MEK/IPA, a temperature decrease from 24.8 to 18.4 °C caused a change from complete dissolution to combined swelling/dissolution behavior and rendered the PMMA film only 68% soluble. Kinetic effects were determined by dissolution and penetration rate measurements. A constant penetration velocity was observed for almost all compositions for both binary solvent mixtures with Case II transport assumptions providing good agreement with experimental results. For MEK/IPA, penetration rates increased with increasing MEK concentration. For MIBK/MeOH, however, a maximum was observed at 60:40 MIBK/MeOH.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRaman study of the preparation of silica- and alumina-supported titania from titanium tetramethoxide and nitric acidMark G. Reichmann and Alexis T. BellCite this: Langmuir 1987, 3, 4, 563–567Publication Date (Print):July 1, 1987Publication History Published online1 May 2002Published inissue 1 July 1987https://pubs.acs.org/doi/10.1021/la00076a022https://doi.org/10.1021/la00076a022research-articleACS PublicationsRequest reuse permissionsArticle Views89Altmetric-Citations4LEARN 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

A theoretical study was conducted to investigate the chemical nature of an unusual interaction observed between carbonyl and acetate ligands in the Rh(CO)2(CF3COO)3 complex. This interaction is intriguing because it is only nominally longer (0.1−0.2 Å) than a typical carbon−oxygen σ bond, yet is associated with only a modest (∼10 kcal/mol) energy lowering of the complex. A localized bonding molecular orbital that promotes the notion of charge sharing is present between the interacting ligands. Constrained geometry optimizations in tandem with Mulliken population analyses indicate that the interaction stems from the inability of Rh(III) with highly electron withdrawing ligands to back-donate properly into the carbonyl ligands. This produces a charge imbalance in the ligands, which sets the stage for nucleophilic attack by the acetate oxygen to the carbonyl carbon. This interaction causes a shift in the predicted values of both IR and 13C NMR signals, which are compared to experiment. For a full explanation of the 13C NMR shifts, two explicit solvent molecules were added to the model and found to induce interaction of both carbonyls with acetate ligands. The chosen density functional (B3LYP) and basis set were validated by comparing theoretically predicted structures and vibrational frequencies with experimentally determined values for several complexes.