A series of materials containing nickel and aluminium ions has been prepared by coprecipitation with alkaline solutions, under various conditions, from solutions of the nitrates. The composition and structure of the precipitates has been examined using a number of techniques including chemical analysis, X-ray diffraction, thermogravimetry and infrared spectroscopy. The precipitates have structures typical of minerals of the hydrotalcite group and particularly of the nickel-aluminium compound, takovite. They consist of brucite-like layers of composition [Ni,Al,-,(OH),](1-2)+ and interlayers containing CO:-, NO, or OH-ions, or combinations of these, depending on the preparation conditions, together with molecular water; the anions balance the excess charge of the brucite layers. It is concluded that the aluminium ions are randomly substituted for nickel ions in the brucite layers and that the structure of these layers is independent of the anions in the interlayer. For freshly precipitated samples, 0.5 < x 5 0.85, but for hydrothermally aged materials, 0.66 6 x 6 0.75; outside these ranges, boehmite or Ni(OH), form as separate phases. The results are compared with those for precipitates prepared from ammoniacal solutions and it is concluded that the two types of material are indistinguishable.
Resplts are presented for the total and metallic nickel areas of a series of coprecipitated nickel-alumina catalysts prepared and pretreated in different ways. The total areas of the samples decrease on reduction and with increasing reduction temperature, while the nickel area increases with reduction temperature. Increasing calcination temperature causes a decrease in total and nickel areas, this being particularly marked at high temperatures of calcination. A model for the catalyst system is proposed, based on these results and on complementary structural investigations. The high stability of the catalysts is attributed to the presence in the unreduced catalyst of nickel oxide rich phases containing dissolved aluminium ions; on reduction, alumina crystallises on the surface of the growing nickel crystallites, preventing sintering of the catalysts except under extreme conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.