【作者】 付真金；

【导师】 胡常伟；

【作者基本信息】 四川大学 ， 物理化学， 2003， 硕士

【摘要】 本文在常温常压下，采用以Ni为主的系列催化剂，研究了不同反应条件下由苯催化氧化制备苯酚的反应活性，并采用XRD，TPR和XPS对催化剂晶相结构特征、还原行为及表面状态进行了表征。 采用不同载体，制备了仅含Ni的系列催化剂，活性测试表明，在本文条件下，以γ-Al₂O₃为载体的催化剂活性最好，分子筛次之，再次是TiO₂，然后是活性炭，SiO₂为载体的活性最差。 在γ-Al₂O₃为载体，Ni为主催化成分并引入其它三种金属元素共存的系列催化剂上进行的苯直接氧化制备苯酚反应表明，Ni负载量为3wt％的催化剂效果较好。同时，该催化剂未经还原直接使用时的催化活性比经H₂还原后使用时的效果好，其活性还受催化剂用量、氨水用量、苯用量、过氧化氢用量及氨水的浓度的影响。 Ni3／γ-Al₂O₃催化剂中添加Ce、Ca或Pt后催化剂的活性降低。同时，反应后，仅含Ni催化剂经H₂还原后可再生，而添加助剂的催化剂再生能力有所降低。 用XRD，TPR及XPS对这一系列催化剂进行表征，结果表明，含四组分催化剂的活性相是由高分散的Ni物种衍生而成的，晶相镍氧化物及单质镍对该反应无活性，Ce、Ca、Pt的添加使得Ni的负载量降低，影响了这种高分散的Ni状态，从而使催化剂活性降低了。通过TPR研究发现，载体不同，Ni在载体上分散性好且易还原的催化剂活性好。但这种易还原物种量超过催化剂最佳活性量时，也会使活性下降。 对Ni3／γ-Al₂O₃催化剂实验条件进行优化实验设计。采用正交试验设计方法，对影响苯酚收率的因素进行了优化设计和实验，用正交表L₂₅（5⁶）来安排实验。对实验中的六个因素：反应时间、氨水用量、过氧化氢用量、反 四川大学硕士学位论文应温度、催化剂用量和苯用量，各作了五个水平的考察，找到一个该条件下的最优方案。最优反应条件是:温度40℃、反应时间4.5h、氨水50ml、苯25ml、过氧化氢10ml、催化剂19。采用最优化方案进行的实验证明，优化所得的这个方案的确是最优方案。找到苯为该反应的主要影响因素，对该反应的影响因素从主到次的顺序是:苯，氨水，过氧化氢，催化剂，反应时间，反应温度。 最后对本实验的反应机理作了可能性的推测，认为本实验的反应机理可能是: NH3+（）一（NH3）（3 .8） HZOZ一珑O+[O]（3.9） 【01+（NH:）一（O）+NH3（4.0） C6H6+（O）一（C6HSOH）（4.1） （C6HsOH）^C6HSOH+（）（4.2） 注:（）活性中心，〔O]活泼氧更多还原

【Abstract】 The activities of a series of Ni containing catalysts were studied under mild conditions. The phase composition, reducibility and surface structure of the catalysts were investigated by using X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) techniques.Different support materials were used to prepare the catalysts, it was observed that these catalysts show different activities. When y -Al2O3 is used as support, the catalyst shows the highest activity, then molecular sieve, TiO2, activated carbon and SiO2 in a decreasing order.A series of Ni containing gamma-Al2O3 catalysts promoted by other three components were prepared and used in the direct oxidation of benzene to phenol. The results show that the catalyst with Ni loading up to 3wt% has the highest activity. Several parameters, such as the amount of catalyst used, the amount of ammonia, the amount of benzene, the amount of hydrogen peroxide and the concentration of ammonia also affect the performance of the catalyst.The additions of Ce, Ca or Pt on Ni3/gamma -Al2O3 catalyst does not enhance the catalytic performance of the samples for the target reaction, and a remarkable decrease in activity was observed. The used Ni3/ gamma -Al2O3 catalyst could be regenerated by H2 reduction.XRD, TPR and XPS characterizations indicate that the active phase for the target reaction may be originated from highly dispersed nickel oxide, while the presence of crystallites nickel oxides or nickel metal may reduce the activity. Theaddition of Ce, Ca or Pt may result in a decrease of nickel loading and the dispersion state of nickel, and then reduce the activity and stability of the catalyst. For different supports used, TPR profiles show that the catalysts with well-dispersed nickel oxide species and reducible at low temperature show high activity.L25(56) orthogonal design was used to optimize the experimental parameters for the direct hydroxylation of benzene by hydrogen peroxide over Ni3/gamma-Al2O3 catalyst. The six factors chosen for test are as the following, the reaction time, the amount of ammonia used, the amount of hydrogen peroxide used, reaction temperature, the amount of catalyst and benzene used, each with five levels. The result of the experiment carried out using the optimized conditions confirms that orthogonal design is really a perfect one for optimality catalyzed reaction conditions (reaction temperature 40,reaction time 4.5 hour, ammonia 50 ml, benzene 25 ml, H2O2 10 ml, catalyst Ig).Finally, we speculates the possible reaction mechanism as follows:更多还原