CHARACTERIZATION OF THE NI(II) PHASE FORMED ON SILICA UPON DEPOSITION-PRECIPITATION

The nature of the Ni(II) phase formed on silica during the preparation by deposition-precipitation (DP) of Ni/SiO2 samples is shown to depen d on the silica surface area and the time of deposition -precipitation . Ni/SiO2 samples have been characterized by XRD, IR, EXAFS, TPR, TEM, STEM-EDX, and BET. With silica of low surface area and for short DP t ime (less than or equal to 4 h), the Ni(II)) phase is mainly a turbost ratic nickel hydroxide with a small amount of 1:1 nickel phyllosilicat e. However, silica of high surface area and for short DP lime (less th an or equal to 100 min), the Ni(II) phase is mainly a I:1 nickel phyll osilicate. For longer DP time (>4 h) and with both types of silica, th e Ni(II) phase is an ill-crystallized 1:I nickel phyllosilicate. Howev er, the latter is better crystallized with silica of low surface area. Almost the same Ni(II) phases were obtained whether silica was porous or not. However, the Ni(II) phase is better crystallized and the inte rface with the support is larger with nonporous silica than with porou s one.