Characterization of Ni/TiO2 catalysts prepared by successive adsorption-reduction of Ni2+ ions

Three Ni/TiO2 samples have been synthesized by impregnation (sample Ni-i-Ti ), adsorption of Ni2+ ions from alkaline media on TiO2 (sample Ni-1-Ti) and on reduced Ni-1-Ti (sample Ni-2-Ti). The samples have been characterized b y TPR, IR spectroscopy of adsorbed CO and X-ray diffraction. Impregnation l eads to a less homogeneous distribution of the active phase and a negligibl y lower temperature of reduction as compared with the adsorption technique. Reduction of Ni-i-Ti results in the formation of nickel particles with an average diameter of 22 nm. Surface Ni-0 was detected by CO testing. The ave rage diameter of the nickel particles in the reduced Ni-1-Ti sample is abou t 20 nm. In this case, however, no metal nickel was detected on the surface , i.e. the metal particles are encapsulated in the support. The majority of the active sites for adsorption are regenerated during the reduction of ni ckel in Ni-1-Ti, which allows Ni2+ ions to be adsorbed again on the sample. As a result, the nickel concentration increases. The mean diameter of the nickel particles on reduced Ni-2-Ti remains of the order of 20 nm, similar to the case of the reduced Ni-1-Ti sample. With Ni-2-Ti, however, surface m etal nickel was detected by CO adsorption. It is concluded that successive absorption-reduction of Ni2+ ions might be used to prepare titania supporte d nickel catalyst with a desired nickel concentration and metal particles t hat are not encapsulated in the support. Some new aspects of the strong met al-support interaction (SMSI) mechanism are also discussed.