【作者】 辛俊娜；

【导师】 吕连海；

【作者基本信息】 大连理工大学 ， 应用化学， 2008， 博士

【摘要】 负载型纳米Pd基催化剂由于其优异的催化活性和选择性,被广泛应用于芳香化合物和芳香硝基化合物的选择性催化加氢反应中。传统的浸渍法工艺,易造成Pd纳米粒子团聚和分散不均匀。与传统工艺相比,采用保护剂化学还原法制备的纳米Pd基催化剂具有Pd粒径小且分布窄的优点,但由于现在所选用的制备方法和保护剂类型的限制,得到的催化剂稳定性不好,使用寿命较短,且工艺仍十分复杂,限制了其应用。本文从寻找新的保护剂种类,简化制备工艺以提高催化性能方面进行了研究,提出了一种新型的方法。采用两种非离子表面活性剂Tween-20和Brij-35作为保护剂,NaBH₄作还原剂,以水为反应介质,不加入任何有机溶剂,根据载体的不同性质,从两种不同的合成工艺路线,制备了分别负载于活性碳、Al₂O₃、TiO₂、SiO₂几种载体上的纳米Pd基催化剂;采用TEM、XRD、ICP和SEM等对其结构特征进行了表征;考察了其在几种典型的双环芳香化合物和芳香硝基化合物的选择性催化加氢反应中的催化性能。以两种非离子表面活性剂Brij-35和Tween-20作为保护剂,采用合成路线一先还原后负载的方法,用NaBH₄还原制备了负载量为4%、5%和10%Pd/C的催化剂。由于Pd纳米粒子受到表面活性剂的保护,Pd纳米尺寸有效地控制在2-4 nm之间。海绵状的Pd纳米晶高度分散在活性碳载体的表面,每个Pd纳米晶均是由多个2-4 nm的Pd纳米粒子组成,并且随着Pd的负载量的增加,可以形成非晶态Pd₂B化合物。采用路线二先负载后还原的方法,制得了5%Pd/Al₂O₃和Pd/SiO₂催化剂,并且用两种制备路线制得2.5%Pd/TiO₂催化剂,这三种催化剂Pd纳米微粒均匀地分散在载体的表面和孔道中,不具有Pd/C催化剂的海绵状Pd纳米晶结构,Pd的纳米粒径在2-4 nm之间。以10%Pd/C作催化剂,选择性液相催化加氢对羟基联苯的制备对环己基苯酚。在优化的反应条件140℃、3.5MPa下,以THF取代了文献中报道的腐蚀性的乙酸作溶剂,对环己基苯酚的收率高达92.3%。采用浓度为1wt%-2.5wt%NaOH溶液和甲苯辅助萃取的方法可以有效地将对环己基苯酚从加氢产物中分离出来,对环己基苯酚的收率高达95%。以α-萘酚（NP-OH）液相选择性催化加氢反应为对象,乙醇作溶剂,考察了2.5%Pd/TiO₂催化剂的催化性能。NP-OH的加氢产物由两种四氢产物（THNol）,四氢萘酮（Tetralon）和四氢萘（THN）组成,无全加氢产物十氢萘生成。反应机理研究表明该反应是一个复杂的平行连串反应。1,2,3,4-THNol证明是由中间体四氢萘酮进一步加氢后得到,1,2,3,4-THNol继续加氢后发生脱羟基反应转化为THN的速率要高于5,6,7,8-THNol转化的速率,反应条件的控制将影响NP-OH的加氢产物分布,在优化的反应条件140℃,2.6MPa下,1,2,3,4-THNol的收率高达46.3%,该值远高于当前文献报道的结果。以5%Pd/C作催化剂,高选择性液相催化加氢喹啉制备1,2,3,4-四氢喹啉（py-THQ）,在优化的反应条件125℃,3.0MPa下,喹啉的转化率达到100%,py-THQ的选择性达到99.7%。反应过程中生成的中间产物吸附在Pd/C催化剂的活性位使其在二次循环中失活。将催化剂用溶剂反复洗涤后,活性基本可以恢复。以4%Pd/C作催化剂,温和条件下高选择性催化加氢8-羟基喹啉（8-Qol）制备8-羟基-1,2,3,4-四氢喹啉（1,2,3,4-THQol）,优化的反应条件:温度100-120℃,压力2.0-2.5MPa,原料浓度3-4g/30ml MeOH,反应时间在1-2 h,原料100%转化,1,2,3,4-THQol的收率高于98.5%。将负载于Al₂O₃、C和TiO₂三种载体上的Pd基催化剂分别应用于4-硝基邻苯二甲腈（4-NPN）选择性还原制备4-氨基邻苯二甲腈（4-APN）的反应当中,三种催化剂对4-NPN的加氢反应的速率大小顺序为:Pd/Al₂O₃＞Pd/TiO₂＞Pd/C,三种催化剂的使用寿命顺序为:Pd/Al₂O₃＞Pd/C＞Pd/TiO₂。Pd/Al₂O₃表现出最高的催化活性,在优化的反应条件80℃、0.6Mpa、原料浓度0.64mol/L、45min下,4-APN的收率高于99.7%,催化剂连续循环14次后,仍能在80℃时使原料100%转化,采用本方法制备的Pd基催化剂可以大大提高4-APN的产率。将5%Pd/C催化剂用于邻、间、对氯代硝基苯的选择性加氢反应中,不需要加入任何脱氯抑制剂,氯代芳胺的选择性在第二次循环后均在99%以上,催化剂进入稳定期后选择性均保持在100%。该催化剂对邻、间、对氯代硝基苯加氢反应的速率大小为:对位＞间位＞邻位,在催化剂活性进入稳定期后,在反应压力2.5MPa下,反应温度分别在130℃、120℃、110℃下,反应3h,邻、间、对氯代硝基苯的转化率达到100%,氯代芳胺的选择性均保持在100%。催化剂可连续套用40次,活性保持不变。更多还原

【Abstract】 Supported Pd catalysts are widely used in selective hydrogenation of aromatics and reduction of nitroaromatic compounds due to their excellent catalytic activity and seletivity. The traditional impreganation process for preparation of supported Pd catalysts usually resulted in aggregation of Pd nanoparticles and low dispersion.Comparing with the conventional process,chemical reduction method with protection agents can prepare smaller nanosize Pd particles with high dispersion.At present,due to the limitation of the categories of protecting agentst,the supported catalysts prepared from this method still exist some problems such as short catalytic life,instability,complicated procedures and so on.In this work,we have developed a new technical process to prepare supported nano-Pd catalysts by using mixture of laurylether（Brij-35） and sorbitanmonolaurate（Tween-20） as binary stabilizing surfactants.Pd nanoparticles were obtained by chemical reduction of chloropalladium acid（H₂PdCl₄） with sodium borohydride（NaBH₄） in aqueous solution without any organic solvent.According to the properties of different supports,the preparation procedure was typically designed by two routes.We prepared four series of supported nano-Pd catalysts on different carriers including C,Al₂O₃,TiO₂ and SiO₂.The microstructure of supported Pd catalysts was characterized by means of TEM,XRD,ICP and SEM.The catalytic activity of supported nano-Pd catalyst was tested in several typical probe reactions including selective hydrogenations of bicyclic and nitro-aromatic compounds.Pd/C catalysts with different Pd loading amount 4wt%,5wt%and 10wt%were prepared from Route No.1 first reduction then support using Brij-35 and Tween-20 as protection agents. Well-dispersed Pd particles measuring 2-4nm were successfully prepared without aggregation. Both Tween-20 and Brij-35 were proved to be suitable for our purposes.Sponge-like nano-Pd crystals were highly dispersed on the surface of active carbon.Simultaneously,the spong-like Pd nanocrystals consist of several nano-Pd particles in the nanometric size rang 2-4nm.The amorphous Pd₂B compound may be formed with increasing Pd loading amount of Pd/C catalyst.5%Pd/Al₂O₃ and 5wt%Pd/SiO₂ were prepared from Route No.2 first support then reduction and 2.5wt%Pd/TiO₂ from both routes.Pd nanoparticles with the average size of 2-4nm in above three catalysts were highly dispersed on the surface and inside pores of the support without the formation of sponge-like nano-Pd crystals. The hydrogenation of p-phenylphenol（p-PP） can be regioselectively performed to produce p-cyclohexylphenol（p-CP） by using 10wt%Pd/C catalyst.The selectivity of p-CP can be as high as 92.3%at 413 K,3.5 MPa when the conversion of p-PP is 100%.THF is an effective solvent for the reaction which can successfully replace the corrosive acetic acid as reported in previous patent,p-CP can be separated and purified by using aqueous NaOH solution and toluene extraction,giving rise to 95%yield of separation and 99.9%high purity p-CP.2.5wt%Pd/TiO₂ was examined for the partial hydrogenation of 1-naphthol（NP-OH） in EtOH solvent.The hydrogenation products consist of tetrahydronaphthols（THNols）,tetralone and tetralin（THN） without the formation of decaline.Kinetic study proved that the reaction was a complicated one containing multi-step parallel and consecutive hydrogenations. Tetralone was an intermediate for the hydrogenation of NP-OH to 1,2,3,4-THNol.Further hydrogenation of THNol to THN occur faster from 1,2,3,4-THNol than from 5,6,7,8-THNol. The 1,2,3,4-THNol selectivity can be up to 46.3%under 140℃,2.6MPa with 100% conversion of NP-OH.It is very important to optimize the pressure,reaction temperature, reaction time as well as catalyst in order to reach high 1,2,3,4-THNol selectivity.Selective hydrogenation of quinoline over 5wt%Pd/C catalyst in liquid phase gave rise mainly to 1,2,3,4-tetrahydroquinoline（py-THQ）.High regioselectivity of py-THQ was up to 99.7%under 125℃,3.0MPa,3h when the conversion was 100%.The reaction intermediates were responsible for the catalyst deactivation in the second run.However,catalytic activity of the catalyst could be almost recovered through washing it repeatedly with organic solvent. Partial hydrogenation of 8-quinolinol（8-Qol） to 1,2,3,4-tetrahydroquinolinol（1,2,3,4-Qol） was performed over 4wt%Pd/C catalyst under mild conditions.Selectivity of 1,2,3,4-Qol 98.5%was obtained under optimized conditions of 100-120℃,2.0-2.5MPa,concentration of raw material 3-4g/30ml MeOH within reaction time 1-2h with 100%conversion.Hydrogenation of 4-nitrophthalonitrile（4-NPN） was studied under mild conditions over supported Pd catalysts.The influence of various reaction parameters and the effect of different support were investigated.The hydrogenation rate was dramatically affected by the property of supports.The hydrogenation rate increases in the order:Pd/Al₂O₃＞Pd/TiO₂＞Pd/C and the catalytic life increases in the order:Pd/Al₂O₃＞Pd/C＞Pd/TiO₂.Pd/Al₂O₃ catalyst exhibited the best activity and longest lifetime.Under optimized conditions of 80℃,0.6 MPa and concentration of raw material 0.64 mol/L,45min,the yield of 4- aminophthalonitrile （4-APN） was up to 99.7%with 100%conversion of 4-NPN.The Pd/Al₂O₃ was repeatedly used for 12 times and kept 100%conversion of 4-NPN and high yield of 4-APN,indicating excellent stability. 5wt%Pd/C catalyst was applied in selective hydrogenation of chloronitrobenzenes（CNBs） with no addition of dechlorine inhibitors.An induction period of the catalyst performance was observed.The hydrogenation rates of different CNBs over Pd/C were dramatically affected by the position of substituent -Cl group.The reaction rates increased in the order of p-＞m-＞o-Effects of various reaction parameters were investigated after the induction period.When the reaction pressure was set to 2.5MPa and reaction time of 3h,the conversion of o-,m- and p-CNB were all up to 100%at different temperature of 403K,393K,383K,and selectivity to the corresponding CANs were 100%.The catalyst can be repeatedly used for 40 runs with 100%conversion of the CNBs.更多还原