载体对Ni_2P催化剂加氢脱氮反应性能的影响

使用TiO2、Al2O3以及TiO2-Al2O3复合载体考察了载体对磷化镍催化剂活性相和加氢脱氮性能的影响。不同钛铝原子比的TiO2-Al2O3复合载体采用原位-溶胶凝胶法制备,负载的磷化镍催化剂采用等体积浸渍法和H2原位还原法制备。以喹啉为模型化合物在固定床反应器上对催化剂的加氢脱氮性能进行评价,采用XRD、N2吸附、TEM和H2-TPR等技术对催化剂和载体进行了表征。结果表明,制成的复合载体基本保留了最初引入的γ-Al2O3的孔特征,分散在γ-Al2O3表面的TiO2以锐钛矿晶型存在。不同载体对催化剂的H2还原行为有显著影响,所形成的活性物种也不相同。Al2O3中引入TiO2可以减弱P物种和Al2O3之间的相互作用,有利于Ni2P活性相的生成和催化活性的提高。当Ti/Al的原子比为1∶8时,Ni2P/TiO2-Al2O3催化剂比Ni2P/TiO2、Ni2P/Al2O3催化剂具有更高的加氢脱氮活性。

Effects of support on hydrodenitrogenation activity of nickel phosphide catalysts

The effects of the support on active site formation and hydrodenitrogenation(HDN) activity of nickel phosphide catalysts were examined, using TiO₂, Al₂O₃ and TiO₂-Al₂O₃, composite supports. A series of TiO₂-Al₂O₃ prepared by hydrolysis and deposition of tetrabutyl titanate on macropore Al₂O₃, and the supported nickel phosphide catalyst, were prepared by incipient wetness impregnation and in situ H₂ reduction method. The samples were characterized by X-ray diffraction(XRD), BET surface area, transmission electron microscopy(TEM) and H₂ temperature-programmed reduction(H₂-TPR).Their hydrodenitrogenation(HDN) performance were evaluated on a continuous-flow fixed-bed reactor by using quinoline as the model molecules. The results showed that the TiO₂-Al₂O₃ composite support still retained the pore properties of macropore Al₂O₃, and TiO₂ were well dispersed on the Al₂O₃ surface in the form of anatase. Different supports have great influence on the reduction behaviour of the oxidic precusors and HDN activity of phosphide catalysts. The main active phase after reduction was Ni₂P phase for the TiO₂ and TiO₂-Al₂O₃ supportd catalyst, but only Ni₁₂P₅ appeared for the Al₂O₃ supported catalyst. The order of HDN activities of nickel phosphide reduced at optimal reaction conditions was TiO₂-Al₂O₃ > Al₂O₃> TiO₂. TiO₂-Al₂O₃ supported catalyst with the Ti /Al atomic ratio of 1:8 exhibited the highest HDN activity among all catalysts. The presence of TiO₂ weakened the strong interaction between the Al₂O₃ and phosphate, and contributed to the formation of Ni₂P active phase and the improvement of HDN activity.