NiWN_x/γ-Al_2O_3催化剂的表面性质及加氢脱氮性能

SURFACE PROPERTIES AND HYDRODENITROGENATION ACTIVITY OF NiWN_x/γ-Al_2O_3 CATALYST

分别采用浸渍法和混合法,通过在H2和N2混合气中程序升温还原反应的氮化处理技术,合成了Ni WNx/γ-Al2O3催化剂。采用TG-DTA考察了氮化过程,采用BET、XRD、XPS等手段表征了合成的催化剂,并以吡啶为模型化合物考察其加氢脱氮性能。结果表明,两种方法制备的催化剂的氮化过程明显不同;钝化会在催化剂表面形成氧化层,但不改变其体相结构,而使浸渍法制备的催化剂表面高价态钨量较多;Ni WNx/γ-Al2O3催化剂的比表面积可以达到187m2/g;由浸渍法制备的硫化和氮化镍钨催化剂的加氢脱氮性能都较高,脱氮率最高可以达到98.5%(360℃反应)。在14h的HDN实验中,由浸渍法制备的催化剂显示出较高的活性和稳定性,而由混合法制备的催化剂的脱氮率则在反应6h后降低。

The nitride catalyst of NiWNx/γ-Al2O3 was synthesized by impregnation and blend method and nitrided with N2-H2 mixture in process of temperature programmed reduction. The nitrification of catalysts was investigated by TG-DTA and the surface properties of catalysts were characterized by BET, XRD and XPS techniques. The hydrodenitrogenation （HDN） activity of pyridine over the catalyst was examined. The results showed that the BET area of the catalyst was 187 m^2/g. There was a certain amount of oxygen element on the surface of the passivated catalysts. The surface species could be composed of tungsten oxynitrides including W^6＋, W^4＋ and W^0-W^2＋ species. But the crystal structure of catalysts did not change in passivation process. The HDN activity of the catalysts synthesized by impregnation was obviously higher than that by blend. The highest denitrification percent was 98.4 % at reaction temperature of 360℃. During the 14 h HDN reaction the NiWNx/γ-Al2O3 prepared by impregnation showed the high and stable activity and was a kind of useful catalyst with potential value in industry, while the denitrification percent of NiWNx/γ-Al2O3 prepared by blend method was reduced after 6 h reaction.