【作者】 陈渝；

【导师】 樊森清； 王文国；

【作者基本信息】 四川大学 ， 化学工程（专业学位）， 2022， 硕士

【摘要】 纳米催化材料是反应过程中不可缺少的重要介质,在实际工业应用中一般需要通过造粒将其制备成具有特定形状的大颗粒。成型后的大颗粒催化剂在用于固定床/流化床反应器时,会存在明显的内扩散和外扩散效应。此外,催化床层中不均匀的空隙尺寸和空隙率,使得反应流体不能均匀地流过催化床层,并由此带来停留时间、温度场以及浓度场的非均匀分布,从而影响催化反应效果。针对上述问题,本文通过原位合成的方法将纳米催化材料以游离分散的状态固载于微纳尺度的膜孔道内以得到催化膜纳反应器（catalytic membrane nano reactor,CMNR）,并采用所构建的CMNR用于对硝基苯酚（p-NP）加氢反应以评测性能强化行为。主要研究内容和结果如下:（1）通过离子交换法将ZIF-8衍生的银纳米颗粒（Ag nano particles,Ag NPs）固定在聚醚砜（PES）多孔膜的膜孔道中,以形成Ag/PDA/PES CMNR。根据X射线单晶衍射（XRD）、X射线光电子能谱（XPS）、衰减全反射红外光谱法（ATR-FTIR）等表征方法,描述了CMNR制备过程中的离子交换行为;采用场发射扫描电子显微镜（FE-SEM）、透射电子显微镜（TEM）对膜孔道内的催化剂分布、粒径进行了分析,其结果表明经过离子交换法制备得到的Ag NPs的粒径为4.55±1.67 nm,比未采用离子交换法制备得到的Ag NPs缩小了5倍;采用电感耦合等离子体发射光谱仪（ICP-OES）对催化剂的含量进行了测试,结果表明Ag NPs在膜孔道内的含量为11.8 g·m^-2,比未采用离子交换法制备得到的CMNR高了5倍。在p-NP的加氢催化中,当膜通量为127 L·m^-2·h^-1,Na BH₄与p-NP之比为500:1的条件下,p-NP的转化率为99%,对应的表观反应速率常数(k_app)为104.4 min^-1,比未采用离子交换法制备得到的CMNR的k_app高出2个数量级。（2）通过流动合成法和置换法将Cu-Ag双金属纳米颗粒（Cu-Ag nano particles,Cu-Ag NPs）固定在PES膜的膜孔道中,以形成Cu-Ag/PES CMNR。采用TEM对双金属核壳纳米结构进行了分析,其结果表明所制备得到的Cu-Ag双金属为“点缀型”核壳结构;采用XPS表征证明了Cu-Ag双金属之间存在着电子偏移行为;采用p-NP的加氢催化行为,研究了Cu-Ag/PES CMNR的催化强化行为。其结果表明:在“点缀型”核壳结构中,Ag NPs分散在Cu核上可以提高Ag NPs的分散性和利用率;双金属组分之间的电子偏移现象可以促进高电子密度活性位点的形成,有利于产生具有强还原性的活性氢用于加氢反应;膜孔道的分散性可以防止Cu-Ag NPs出现超过膜孔尺度的团聚,强化反应物和催化剂之间的接触;最后,在穿流过膜的反应操作模式下,可以强化反应物和催化剂之间的质量传递。（3）通过流动合成法和置换法将Cu-Ag_x（其中x是AgNO₃的毫摩尔浓度）双金属纳米颗粒（Cu-Ag_x NPs）固定在膜孔道中,以形成Cu-Ag_x/PES CMNR。采用XPS和ICP-OES对Cu-Ag_x NPs中的元素含量进行了分析,其结果表明Ag元素主要分布在催化剂颗粒的表面;采用XPS和H₂程序还原升温（H₂-TPR）技术证明了双金属之间存在着显著的电子相互作用;采用p-NP的加氢催化行为,研究了Cu-Ag_x NPs中活性元素含量的不同对催化性能的影响,并提出了Cu-Ag_x NPs用于p-NP加氢催化的机理:在催化过程中,Cu作为一个缺电子的位点来吸附和活化p-NP的-NO₂基团,而Ag则有利于活性H溢流到Cu表面,然后完成p-NP的加氢催化。根据Ag元素的含量和k_app作图,可以得到一个火山状的k_app分布图,其中,k_app先随着Ag含量的增加呈现出增大的趋势,然后随着Ag含量的进一步增加呈现出下降的趋势。由于最适的吸附活化行为和最佳的氢溢流行为,固定Cu-Ag₂NPs的CMNR具有最大的k_app,为1071 min^-1（Na BH₄与p-NP之比为100:1）。更多还原

【Abstract】 Nano catalytic materials are indispensable and important media in the reaction process.In practical industrial applications,nano catalytic materials generally required to be prepared into large particles with a specific shape by granulation.The prepared large particle catalysts are subject to significant internal and external diffusion effects when used in fixed/fluidized bed reactors.In addition,the reaction fluid cannot flow uniformly through the catalytic bed due to the heterogeneous void size and void ratio in the catalytic bed,resulting in a non-uniform distribution of residence time,temperature and concentration fields,which affects the catalytic reaction effect.In this paper,the catalytic membrane nanoreactor（CMNR）was obtained by in-situ synthesis of nano catalytic materials in membrane pores with micro-/nano-scale,and the prepared CMNRs were used for the hydrogenation of p-nitrophenol（p-NP）to evaluate the enhanced performance.The main studies and results are as follows:（1）An Ag/PDA/PES CMNR was obtained by immobilizing ZIF-8-derived Ag nanoparticles（Ag nano particles,Ag NPs）in the membrane pores by ion-exchange methods.The ion-exchange behavior during the preparation of CMNR was characterized by X-ray single crystal diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,and Attenuated total reflection infrared spectroscopy（ATR-FTIR）.The catalyst distribution and particle size in the membrane pores were characterized by Field emission Scanning electron microscopy（FE-SEM）and Transmission electron microscopy（TEM）.The results showed that the particle size of Ag NPs obtained by ion-exchange methods was 4.55±1.67 nm,which was 5 times smaller than that of the Ag NPs not prepared by ion-exchange methods.The catalyst content was tested by Inductively coupled plasma optical emission spectrometry（ICP-OES）,and the results showed that the content of Ag NPs in the membrane pores was 11.8 g·m^-2,which was 5 times higher than that of the CMNR prepared without the ion-exchange methods.In the hydrogenation catalysis of p-nitrophenol（p-NP）,the conversion rate of 99%can be achieved under the ratio of 500:1 of Na BH₄ to p-NP and the membrane flux of 127 L·m^-2·h^-1.The apparent reaction rate constant(k_app)of Ag/PDA/PES CMNR obtained by ion-exchange method was 104.4min^-1,which is 2 orders of magnitude higher than the k_app of the CMNR prepared without ion-exchange methods.（2）A Cu-Ag/PES CMNR was obtained by immobilizing Cu-Ag bimetal nanoparticles（Cu-Ag nano particles,Cu-Ag NPs）in the membrane pores by flowing synthesis and displacement method.The nanostructures were characterized by TEM,which showed that the Cu-Ag NPs were prepared in a“dotted”core-shell structure.The existence of electron transfer behavior between Cu and Ag elements was characterized by XPS.And the enhanced catalytic performance of Cu-Ag CMNR was investigated by the p-NP hydrogenation.The experimental results show that in the"dotted"core-shell structure,the dispersion and utilization of Ag NPs can be guaranteed due to Ag NPs is dispersed on Cu.The electron transfer between Cu-Ag bimetallic components can promote the formation of high electron density active sites,which is beneficial to the production of highly reductive active hydrogen.The Cu-Ag NPs agglomeration beyond the membrane pore scale can be prevented due to the dispersion of the membrane pores,resulting in the enhanced contact between reactants and catalysts.Finally,the mass transfer between reactants and catalysts can be enhanced under the mode of flowing reaction.（3）A Cu-Ag_x/PES CMNRs with different active element contents were obtained by immobilizing Cu-Ag_x（where x is the millimolar concentration of Ag NO₃）bimetallic nanoparticles（Cu-Ag_x NPs）in membrane pores by flowing synthesis and replacement methods.The active element content of Cu-Ag_x NPs was investigated by XPS and ICP-OES,which showed that Ag was distributed on the outer surface of catalyst particles.The significant electronic interactions between Cu and Ag elements were characterized by XPS and H₂ Temperature programmed reduction（H₂-TPR）.The catalytic behavior of p-NP hydrogenation was used to investigate the effect of different active element contents in Cu-Ag_x NPs on the catalytic performance.And the mechanism of Cu-Ag_x NPs for p-NP hydrogenation catalysis was proposed that during the catalytic process,the Cu core acts as an electron-deficient site to adsorb and activate the-NO₂ group of p-NP,while the Ag shell is beneficial for enhancing reactive H spilling to Cu surface and then performing hydrogenation.A volcano-like distribution of k_app can be obtained by plotting the Ag content and k_app,where k_app initially shows an increasing trend with increasing Ag content and subsequently shows a decreasing trend with further increases in Ag content.The CMNR with Cu-Ag₂ NPs immobilized has the largest k_app of 1071 min^-1（ratio of 100:1 of Na BH₄ to p-NP）due to the optimum adsorption activation behavior and the best hydrogen spillover behavior.更多还原