摘要
采用高压连续流动微反、XPS、EXAFS等手段考察了硫化温度对NiWF/Al_2O_3催化剂加氢脱氮性能的影响,探讨了加氢脱氮催化剂活性相的组成及在硫化态催化剂中活性组分的存在状态。研究结果表明,经300～400℃硫化的NiWF/Al_2O_3催化剂的加氢脱氮活性最高。当硫化温度为400℃时,W的硫化转化率已达极大(～77%);继续升高硫化温度.对W的硫化转化率影响不大.但使W在催化剂表面的分散度降低;当硫化温度为600℃时,有较完整的WS_2晶体形成。W对加氧脱氮催化剂的活性无直接贡献,W氧化物硫化后转变成WS2,提供了分散活性组分Ni的"初级载体",与Ni共同形成NiWF/Al_2O_3加氢脱氮的活性相。硫化温度在300℃以下时,由于大量的W仍以氧化物的形式存在,显然不利于形成这种由WS_2、Ni共同组成的活性相。当在300～400℃硫化时,Ni在催化剂表面层中的浓度最高,此时结合能为853.0eV的Ni在催化剂中的相对含量也达到极大值。NiWF/Al_2O_3催化剂中Ni的状态及其在表面层中的含量是影响该催化剂加氢脱氮活性的主要因素。
The effect of sulfiding temperature on pyridine hydrodenitrogenation (HDN) activity of NiWF/Al_2O_3 catalyst was studied by means of high pressure continuous flow microreactor, X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS). Emphasis were made on the composition of the active phase of the catalyst and the states of active components of sulfided NiWF/Al_2O_3 catalyst. It was found that NiWF/Al_2O_3 catalyst showed maximum HDN activity at sulfiding temperature of 300-400℃. Tungsten conversion reached its maximum (77%) when sulfiding at 400℃, further increase of sulfiding temperature did not increase the tungsten conversion but decreased the dispersion of tungsten on the Al_2O_3 surface. EXAFS results demonstrated that WS_2 was the main form of tungsten in sulfided NiWF/Al_2O_3 catalyst. As sulfiding temperature being raised, signal of high coordination shell of tungsten appeared,indicating complete WS_2 crystallite gradually resulted. It is considered that tungsten has only indirect effect on the HDN activity, and can be regarded as the 'primary support' of nickel dispersion. At sulfiding temperature lower than 300℃, although most nickel is already in the states capable to form active phase but a large part of tungsten is still in its oxide form which can not be used as 'primary support' for nickel dispersion. So NiWF/Al_2O_3 catalyst did not express its maximum activity until sulfiding at 300-400℃. Depending on the XPS results, it is found that nickel amount reaches its maximum in the surface layer of NiWF/Al_2O_3 catalyst at sulfiding temperature of 300-400℃. Nickel can be classified into four forms depending on its XPS binding energy, one of which has a binding energy of 853.0eV, between NiS (854.9eV) and metal Ni (852.0eV), having strong reductive environment. The amount of this form of nickel shows a clear relation to the HDN activity of NiWF/Al_2O_3 catalyst. It is suggested that the states of nickel and the amount of nickel in the surface layer are the main factors determing the HDN activity of NiWF/Al_2O_3 catalyst. Nickel in the strong reductive environment is the origin of HDN activity.
出处
《石油学报（石油加工）》
EI
CAS
CSCD
北大核心
1994年第2期62-68,共7页
Acta Petrolei Sinica(Petroleum Processing Section)
