焙烧及还原温度对对硝基苯酚加氢合成对氨基苯酚Ni/TiO_2催化剂性能的影响

Effects of Calcination and Reduction Temperature on Catalytic Performance of Ni/TiO_2 Catalyst for Hydrogenation of p-Nitrophenol to p-Animophenol

采用等体积浸渍法制备了Ni/TiO2催化剂,考察了焙烧和还原温度对其结构及催化对硝基苯酚加氢合成对氨基苯酚反应性能的影响,利用X射线衍射、程序升温还原及H2化学吸附等方法对催化剂进行了表征.结果表明,923 K以下焙烧制备的催化剂中镍物种主要以与载体相互作用不同的NiO形式存在,随着焙烧温度的升高,催化剂中NiO与TiO2间的相互作用增强.经723 K还原后,随焙烧温度升高,催化剂的H2化学吸附量减小,而923 K焙烧的催化剂具有较佳的加氢反应性能,这与金属镍和TiOx(x<2)的协同作用有关.对于923 K焙烧的催化剂,当还原温度较低时,NiO还原不完全,金属镍与TiOx的相互作用较弱,催化剂活性较低;当还原温度过高时,镍晶粒发生烧结,并且催化剂的镍活性表面因镍与TiOx的相互作用增强而减小,从而导致催化剂活性降低,适宜的还原温度为673 K.当Ni/TiO2催化剂具有适宜的镍活性表面及适宜的金属镍与TiOx相互作用时,金属镍与TiOx的协同对-NO2的加氢活化最为有利.

The effects of calcination and reduction temperature on the properties of the Ni/TiO2 catalyst were studied by means of X-ray diffraction, temperature-programmed reduction, H2 chemisorption, and the performance evaluation for hydrogenation of p-nitrophenol. The results showed that nickel species existed in the form of NiO in the catalysts calcined at ≤923 K, and the interaction between NiO and TiO2 was enhanced with the increase in calcination temperature. However, nickel species existed in the form of NiTiO3 in the catalyst calcined at 1 023 K. For the catalysts calcined at ≤923 K and reduced at 723 K, there was no remarkable difference in the nickel crystallite size, whereas the amount of H2 chemisorption decreased as the calcination temperature increased, which was due to the increase of the interaction between nickel and TiOx （x 〈 2）. The catalyst calcined at 923 K showed better catalytic performance for hydrogenation of p-nitrophenol than the ones calcined at lower temperatures, which was also closely related to the strong interaction between nickel and TiOx species. The reduction temperature also deeply affected the properties of Ni/TiO2. At low reduction temperature, the catalyst could not be reduced completely, while the high reduction temperature would cause nickel sintering and an excessively strong interaction between nickel and TiOx, leading to a decrease in H2 chemisorption amount, all of which were not beneficial to the catalytic performance. The suitable reduction temperature was 673 K. It was suggested that both amount favored the Key words, nickel; the suitable interaction between nickel and TiOx species and the suitable H2 chemisorption harmonious effect of nickel and TiOx on the activation of the -NO2 group.