Characterization of nickel/silica catalysts during impregnation and further thermal activation treatment leading to metal particles

摘要: Nickel nitrate impregnated onto silica, identified as such after drying at 25[degrees]C, is gradually transformed into basic nickel nitrate, Ni(NO[sub 3])[sub 2][center dot]2Ni(OH)[sub 2], and then phyllosilicate (1:1 phyllosilicate) upon 90[degrees]C. At this temperature, the amount of phyllosilicates which depends on time, can reach 20% overall Ni. The temperature programmed reduction (TPR) profiles exhibit three peaks hydrogen consumption 300, 380, about 500[degrees]C, attributed to decomposition or NiO, 1:1 phyllosilicates, respectively. last peak corresponds Ni content regardless loading conditions 25 This fixed percentage proves that may be still formed beginning TPR. After TPR up 700[degrees]C, totally reduced metal particles have a constant average size 65 A while concentration per surface unit increases with loading. Before complete reduction, are probably located interface between silica remaining nickel,more » for they act anchoring sites. During TPR, decomposition, NiO Ni[sup O] 400[degrees]C without any migration. Between 400 increase in particle due not only but also 0] migration induced by thermal effect weakening strength because phyllosilicates. 47 refs., 8 figs., 12 tabs.« less