We examined active sites for CO2 methanation over Ni/CeO2 catalysts prepared by a wet impregnation method. Four types of Ni/CeO2 with Ni loadings of 1, 3, 5, and 10 wt % were used in this study, assuming that the Ni sites are well dispersed in the catalysts when changing the Ni loading. According to powder X-ray diffraction and scanning transmission electron microscopy, the low-loading catalysts (1 and 3 wt %) consist mainly of Ni–Ce mixed oxides. The results of temperature-programmed reduction by H2 suggested that the Ni–Ce mixed oxides under reducing conditions contain oxygen vacancies (Ni–Vox–Ce). Note that the CO2 conversion rate was proportional to the Ni loading, which probably means that Ni–Vox–Ce sites on the Ni–Ce mixed oxides are active in CO2 conversion. In contrast, when the Ni loading was high (5 and 10 wt %), the catalysts possessed many metallic Ni nanoparticles supported on CeO2 and Ni–Ce mixed oxides. Because the turnover frequencies of CO methanation for 5 and 10 wt % Ni/CeO2 were identical, the presence of a metallic Ni surface could be essential for activation in CO methanation. We focused on the fact that the CO2 conversion rate was not related to the number of oxygen vacancies on CeO2 (Ce–Vox–Ce) but was related to the number of the Ni–Vox–Ce sites. Hence, the formation of Ni–Vox–Ce sites (CO production via the reverse water-gas shift reaction) and the exposure of metallic Ni sites (methanation of the thus-formed CO) are essential for CO2 methanation. Although it has been known that oxygen vacant sites on Ni/CeO2 catalysts are important for the catalytic activity, this study suggested anew that there are two types of the sites, Ce–Vox–Ce and Ni–Vox–Ce. Furthermore, it was clarified that the latter oxygen defect is important for CO2 methanation.

SYNOPSISThe homogeneous grafting of acrylonitrile onto cellulose was carried out in a dimethyl sulfoxide/paraformaldehyde solvent system. The grafted products were added to cellulose/ polyacrylonitrile (PAN) blends as compatibilizers. The thermal decomposition behavior of the blends was investigated by thermogravimetry. The thermal stability of the blends with higher grafted product content was lower by more than 100°C than that of the blends without grafted product. The accessibility values of the former blends were larger than those of the latter. The microphase-separated structures of the grafted product blends were finer than those without the product. Dynamic mechanical measurements and differential scanning calorimetry were performed to estimate the glass transition temperatures, Tg, of the blends. The variation in Tg was smaller than that in characteristic temperatures determined by thermogravimetry. The difference in thermal decomposition behavior was correlated to that in compatibility. Thermogravimetry was found to be effective for estimating the compatibility in cellulose/PAN blends containing grafted products. 0

The reaction of unactivated simple terminal alkynes 1 with allylindiums in THF proceeded smoothly to give the corresponding allylation products 2 in good to high yields. This result is in marked contrast to that of the reaction carried out in DMF, where the allylation of unactivated alkynes was very sluggish. The allylic group of the reagent was attached to the internal carbon of the triple bond, and indium was attached to the less substituted terminal carbon, except for the case of TMS substituted acetylenes 1j and 1k in which the allyl group went to the less substituted carbon of the triple bond. The reaction of unactivated simple terminal and certain internal acetylenes with benzylindium in THF proceeded smoothly to afford the corresponding benzylation products 18 in good to high yields. The benzyl group was attached to the less substituted unhindered carbon of the triple bond, and indium was attached to the more sterically congested carbon. The reaction of activated nitriles 3 with allylindiums in THF at 70 °C gave the corresponding allylation−enamination products 4 in high to excellent yields. This reaction provides a useful method for the synthesis of highly functionalized enamines, which are not easily available via conventional methods. The mechanisms on the above three indation reactions are discussed.

We reported recently that the addition of certain pronucleophiles (HNu) to allenes takes place in the presence of catalytic amounts of palladium complexes (hydrocarbonation reaction) [eqn. ( l)] : monoalkyl substituted or di-substituted

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