【作者】 史荣会；

【导师】 李永红；

【作者基本信息】 天津大学 ， 化学工艺， 2010， 博士

【摘要】 高温蒸汽裂解、催化裂化或热裂化过程所产生的低碳烯烃中常存在微量的共轭二烯烃和炔烃,虽然含量较少,但这些二烯烃和炔烃在烯烃后加工特别是烯烃聚合过程中是有害杂质,需要除去。采用选择性加氢脱除二烯烃是一种有效的手段,制备活性高、选择性好的催化剂是关键所在。本论文对选择性加氢脱二烯烃用非贵金属Ni基催化剂的制备活化进行了研究,设计和研发了一种双助剂金属催化剂,具有良好的二烯选择加氢活性,选择性和稳定性。本文首先对单金属催化剂进行制备、表征及性能研究。采用等体积浸渍法制备一系列镍基催化剂,通过BET,XRD,H₂-TPR,和XPS等表征方法研究了其比表面积、晶相结构、还原温度,还原度和表面元素的价态以及催化剂使用前后性质的变化,并以异戊二烯选择加氢为探针反应,考察了制备方法、制备条件和预处理条件等影响因素,研究了催化剂表面氧化镍与不同晶型氧化铝载体之间的相互作用的区别以及对催化性能的影响。结果表明,以Al（OH）₃为载体前驱体制备的（γ+ ）-Al₂O₃和（κ+θ）-Al₂O₃中活性组分与载体间相互作用的不同并且对催化性能有较大的影响,其中负载量15%左右的Ni/（γ+ ）-Al₂O₃与7.5%左右（κ+θ）-Al₂O₃催化性能较好。当负载量过高时,由于（γ+ ）-Al₂O₃比表面积大,金属分散度高,活性位过多导致催化剂过度加氢,选择性下降,但由于金属载体间强相互作用抑制了表面碳化物沉积使其稳定性提高;而（κ+θ）-Al₂O₃负载的催化剂晶粒较大,活性组分聚集烧结,表面碳化物沉积,导致活性和稳定性下降。为保证催化剂加氢活性的同时,提高催化剂对单烯烃的选择性,对活性较高的7.5% （κ+θ+ ）-Al₂O₃催化剂,进行了预硫化处理,并对硫化条件进行优化,使单烯选择性从0增加至93%。通过CS2催化剂中毒机理的考察,发现CS₂低温下极易使催化剂失活,除了CS2能与催化剂活性中心反应形成金属硫化物外,CS₂在催化剂表面的物理吸附也可能导致催化剂失活。通过共浸渍法加入金属助剂改性后发现,Ce的引入,催化剂的活性和稳定性提高,Cu的加入使催化剂的活性有所降低,但对催化剂对单烯烃的选择性却有明显的提高,而且与无助剂及Ce助剂相比,产物中单烯烃产物分布明显不同。通过对Ni-Ce/Al₂O₃、Ni-Cu/Al₂O₃和Ni-Ce-Cu/Al₂O₃催化剂进行H₂-TPR、BET、XRD,XPS等表征,分析了各种助剂对催化剂性能调变作用机理。对单助剂和双助剂催化剂的加氢作用机理的研究发现,金属Cu首先与载体间发生相互作用,明显提高了金属Ni的还原度,而Ce金属的添加则由Ni、Ce的协同作用促进了活性金属在表面的分散,容易使催化剂表面吸附的二烯烃被加氢,从而提高催化剂的稳定性。针对金属与载体间的相互作用对催化性能的影响,本文选用与（κ+θ+ ）-Al₂O₃中较接近的最稳定氧化铝构型-Al₂O₃作为载体,采用密度泛函理论（DFT）的Dmol3模块,模拟了Ni₄团簇沉积吸附其（0001）面的Ni4/ -Al₂O₃（0001）构型。Ni团簇倾向于同表面不饱和配位的氧原子和铝原子成键。与载体作用后,与纯Ni₄团簇相比,减弱了镍原子之间的结合能,也削弱了气体分子在镍上的吸附,说明载体对活性金属具有分散作用。通过模拟H₂和异戊二烯分子在催化剂Ni₄/ -Al₂O₃（0001）表面上的吸附,为二烯烃加氢反应的机理提供理论数据,为更有效的催化剂体系的设计提供理论参考。更多还原

【Abstract】 Olefins produced by steam cracking, catalytic cracking or thermal cracking processes are associated with few alkynes and dienes invariably. The presence of these compounds is undesirable and harmful to successive process, especially for olefin polymerization. It was a valid means to take selective hydrogenation of dienes to mono-olefins. It was a key method to develop a new hydrogenation catalyst with high activity and selectivity.In this paper, preparation rules and pretreatment conditions of Ni-based catalysts were studied and a Ni-based double promoter catalyst with high activity, mono-olefins selectivity and stabilization was designed and developed. This catalyst possesses good catalytic properties with high activity, selectivity and stability in diene hydrogenation reaction.At first, studies on preparation, characterization and properties of Ni catalysts were performed. Nickel-based catalysts prepared by impregnation were characterized by BET, XRD, H2-TPR and XPS methods to study the surface area, crystal structure, reduction temperature, the chemical valence of surface elements and the used catalyst property changes compared with fresh catalyst. Selective hydrogenation of isoprene was used as a probe reaction to study the effect of different treatment to support and preparation conditions on catalytic activity of Ni-based catalyst. Strong Metal-support interaction （SMSI） and the effect of this interaction on catalytic performance was studied. The results showed that （γ+ ）-Al₂O₃ and （κ+θ）-Al₂O₃ supports obtained by calcination Al（OH）3 and the interaction between the different supports and NiO have great influence on catalytic properties. The catalysts with 15% nickel supported on （γ+ ）-Al₂O₃ and 7.5% on （κ+θ）-Al₂O₃ have good catalytic properties.High nickel loading over （γ+ ）-Al₂O₃ with large surface area, high metal dispersion and too many active sites lead to over-hydrogenation and selectivity decreased, however, carbide deposition on catalyst surface was suppressed to improve the stability by SMSI. Catalysts support on （κ+θ）-Al₂O₃ with weak interaction between metal and support have large sizes of Ni crystal with high Ni loading, which leads to the active component together sintering and surface carbon deposition, resulting in the decrease of activity and stability.To obtain high hydrogenation activity and selectivity of mono-olefins, 7.5% （κ+θ+ ）-Al₂O₃ catalyst was studied by pre-curing treatment. In the optimal curing conditions, the selectivity of mono-olefins can be greatly improved（from 0 to 93%）. By the discussion of poisoning mechanism with CS2,it was found that CS2 easily deactivate the catalyst at low temperature, besides metal sulfide formation, CS2 physical adsorption on the catalyst surface also leads to catalyst deactivation. The method of adding promoter to modify the single Ni catalyst by co-impregnation was applied with the function of the second metal Cu or Ce metal.The modified catalyst can be used to hold good stabilization to selective hydrogenation of isoprene. The introduction of Ce resulted in the higher activity and stability. With Cu modification, the catalytic activity decreased, however, the selectivity of mono-olefins catalyst increased significantly, and olefin products varied significantly compared with Ce and other promoters.Ni-Ce/Al₂O₃, Ni-Cu/Al₂O₃ and Ni-Ce-Cu/Al₂O₃ catalysts were characterized by H2-TPR, BET, XRD, XPS and other characterization methods to study the promoter modulation mechanism on catalytic performance. In the discussion of hydrogenation mechanism of promoters catalysts,it was found that the addition of Cu promoted the interaction between Cu and support and increased the reduction degree of Ni metal significantly, while the addition of Ce with the synergetic effect of two metals increased the degree of metal dispersion. As selective hydrogenation of diene on surface, the stability of catalyst, the stability of catalyst enhanced.To study the effect of interaction between metal and support on the catalytic properties, this paper used the most stable configuration -Al₂O₃ which is closer to （κ+θ+ ）-Al₂O₃ as the support, to simulate the adsorption and deposition of Ni4 cluster on the -Al₂O₃（0001） surface with the Dmol3 module based on density functional theory （DFT）. Nickel clusters tend to coordinate with the unsaturated surface oxygen atoms and aluminum atoms in bonding.The support weakened the binding energy between Ni atoms compared with pure Ni4 clusters, and reduced the H2 molecules adsorption energy on the nickel catalyst, indicating the dispersion effect of active metal by support. This work has calculated isoprene and H₂ molecules adsorption on catalyst Ni₄/ -Al₂O₃（0001） by DFT. The results would provide many theory data for the study of the reaction mechanics in selective hydrogenation and be helpful in understanding real heterogeneous catalytic process.更多还原