Supported nickel catalysts: Preparation and characterisation of alumina-, molybdena-, and silica-supported nickel, and the identification of reactiveoxygen on these catalysts by exchange with isotopically labelled carbon dioxide

Nickel catalysts, supported on alumina, silica, and molybdena, have been pr epared by impregnation and co-crystallization. In the precursor state the c atalysts were characterised by UV-visible spectroscopy, thermogravimetric a nalysis/differential thermal analysis (TGA/DTA), and X-ray photoelectron sp ectroscopy (XPS). The nickel was principally in the 2+ oxidation state with an octahedral coordination. However, the ligand sphere surrounding the nic kel ion was sensitive to the support, indicating that the species on the di fferent supports were not identical thus suggesting a metal complex-support interaction. Reduction was followed by temperature programmed reduction (T PR) and TGA, the results of which indicated that reduction and decompositio n of nickel nitrate occurred simultaneously. X-ray diffraction (XRD) analys is revealed that, with the Ni/MoO3 sample, no hydrogen bronze was formed on reduction. The reduced catalysts were characterised by carbon monoxide che misorption, carbon dioxide chemisorption, and by reaction of buta-1,3-diene with dihydrogen. In the absence of a dihydrogen stream it was found that t he catalysts adsorbed no carbon monoxide due the presence of sub-monolayer quantities of surface oxygen. The extent of the oxygen was quantified by ex change with isotopically labelled carbon dioxide. Differences in the electr onic nature of the nickel between the Ni/MoO3 sample and the other catalyst s were revealed by their behaviour towards buta-1,3-diene hydrogenation.