Room-temperature 129Xe NMR is a convenient means of studying heterogeneous distributions of HMB in N a y , providing the heterogeneity length scales are larger than about 10 pm. Such situations may lend themselves to NMR chemical shift imaging methods in which a linear magnetic field gradient might be used to image xenon profiles in samples possessing macroscopic adsorbate heterogeneities. The suitability of multiple-quantum NMR spectroscopy for probing adsorbate distributions quantitatively is due primarily to the sensitivity of the technique to the number of dipole-dipole coupled spins in a collection of isolated molecules. Counting the number of proton spins in clusters of chemisorbed organic species yields information on their spatial distributions and, thus, about microstructural features of the adsorption sites themselves. Because of the central importance of these sites to the reaction process, multiple-quantum NMR represents a potentially valuable means by which a catalyst's microscopic adsorbate structure can be correlated with its chemical reaction properties. Such information, used in conjunction with the macroscopic adsorbate distributions measured by '29Xe N M R spectroscopy, is key to characterizing intracrystalline mass transport and adsorption of reactant species within zeolitic catalysts. Acknowledgment. We thank D. N. Shykind and M. Trecoske for assistance with the multiple-quantum experiments and with zeolite sample preparation. M. G.Physicochemical characterization of calcined and sulfided CoO/SiO, catalysts were carried out to reveal the interaction modes between cobalt and SiOz using XPS, TPR, TEM, DRS-VIS, and XRD techniques. The CoO/Si02 catalysts were prepared by an impregnation method using cobalt acetate as well as cobalt nitrate and by an ion-exchange technique. It was found that several kinds of cobalt species are formed on CoO/SiO,. These species are assigned to Co304, Co-Si4 mixed oxide, surface Co3+ species, surface silicate, surface Co2+ species in the order of the TPR reduction temperature. Their proportions strongly depended on the starting salt, cobalt content, and preparation method. Cobalt acetate was found to provide highly dispersed CoO/Si02 catalysts with a uniform distribution of cobalt species throughout the catalyst particles as compared to conventionally employed cobalt nitrate. The proportion of Co3+ greatly decreased when cobalt acetate was used instead of cobalt nitrate. All the cobalt species interacting with SiO, were found to be sulfided at 673 K. It was demonstrated that sulfided CoO/Si02 catalysts prepared from cobalt acetate show several times higher hydrogenation activity than the catalysts from cobalt nitrate. On the basis of the XPS characterization of uncalcined precursors, the effects of starting salt on the cobalt-Si0, interaction modes and cobalt dispersion and distribution are discussed.

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The 13C NMR spectra of alkyl vinyl ethers were investigated at 22.5°C with neat liquid at 15.09 MHz. When the alkyl group of the ether becomes more electron-donating, the chemical shift of the α-carbon of the vinyl group shifts to a higher field, and that of the β-carbon, to a lower field. From these results, it was concluded that the contribution of the resonance form, \barCH2–CH=\overset+O–R, in the ether decreases in the order of the increasing electron-repelling power of the alkyl group. Good correlations were obtained between the chemical shifts of the vinyl group and the reactivity of vinyl ether in the cationic reaction. When the ether becomes more reactive, the chemical shift of the α-carbon shifts to a higher field, and that of the β-carbon to a lower field. This fact clearly shows that the attack of the proton on the β-carbon is not the rate determining step in the cationic reaction of the vinyl group. Linear relations were obtained between the chemical shifts of β-methylene protons and of β-carbon, but no correlation was obtained between the chemical shifts of the α-methine proton and of the α-carbon.

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