基于树状聚合物模板的Pt基催化剂的制备及性能研究

发布时间：2018-05-20 22:13

本文选题：树状聚合物 + Pt纳米粒子　；参考：《东南大学》2016年硕士论文

【摘要】：Pt基负载型催化剂由于具有较高的催化反应活性,广泛应用于各类反应中,如低碳烷烃脱氢、一氧化碳氧化、醇的选择性氧化等。一般认为,该催化剂的反应性能与催化剂表面的Pt颗粒的分布以及载体的结构密切相关。传统浸渍法制备的负载型Pt催化剂由于不能有效控制Pt颗粒的尺寸和分布,易于导致催化剂的快速失活。因而如何在制备催化剂的过程中有效控制金属粒子的分散性,并且改善载体的结构,成为改善催化剂反应性能的关键。本文从提高Pt粒子分散性和催化反应活性出发,以聚酰胺-胺型(PAMAM)树状聚合物为模板剂制备了均匀分散的Pt纳米粒子,将其分别负载到介孔A1203、介孔Ce02、介孔Co3O4-CeO2载体上。利用特定条件下的热处理去除聚合物,制备得到不同载体负载的Pt基催化剂。利用多种手段对制备的材料进行了表征分析,并以对硝基苯酚的还原反应为探针反应,结合催化剂的系列表征结果,探讨了催化剂的内在构效关系。以羟基端聚酰胺-胺型树状聚合物为模板剂,通过配位反应封装Pt2+,以硼氢化钠作为还原剂,制备了基于树状聚合物模板的均匀分散的小尺寸Pt纳米粒子(标记为Pt DENs)。而后将其负载到介孔氧化铝(MA)载体上,制得了Pt/MA催化剂。研究了聚合物分解的不同焙烧气氛以及焙烧温度对Pt粒子分布的影响。结果表明,氮气气氛下的焙烧可缓慢分解聚合物,从而能有效控制Pt颗粒间的团聚。同时该气氛下550℃的焙烧既能充分分解聚合物,又能维持Pt颗粒的较小粒径。在催化对硝基苯酚还原反应中氮气下550 ℃处理的催化剂显示最好的催化活性,并且样品易于回收并具有良好的重复使用性。以水热法制备的介孔硅KIT-6作为硬模板,浸渍硝酸铈溶液,经过焙烧和刻蚀后,制备了具有高结晶性的有序介孔氧化铈(meso-CeO2),比表面积为115.3 m2/g。同时,采用溶胶-凝胶法制备了无序孔道的纳米氧化铈材料(nano-CeO2)。然后,将PAMAM树状聚合物封装的Pt纳米粒子分别负载到有序介孔氧化铈和纳米氧化铈载体上,得到Pt/meso-CeO2和Pt/nano-CeO2两种催化剂。研究结果表明,meso-CeO2的高比表面积有利于分散Pt纳米粒子,并且其规整的孔道结构可以限制Pt粒子的团聚,有利于维持Pt颗粒的尺寸。另外,和Pt/nano-CeO2催化剂相比,Pt/meso-CeO2催化剂在对硝基苯酚还原反应中显示出更高的催化反应活性,且具有优良的重复使用性能。以硝酸铈和硝酸钴的混合溶液浸渍到介孔硅KIT-6,经过焙烧和刻蚀后得到有序介孔Co3O4-CeO2复合金属氧化物Co3O4-CeO2将PAMAM树状聚合物封装的Pt纳米粒子固载到介孔Co3O4-CeO2复合金属氧化物载体上,焙烧分解聚合物后得到Pt/meso-Co3O4-CeO2催化剂。Pt纳米粒子负载到Co3O4-CeO2复合金属氧化物后仍维持较小尺寸和良好的分散性,且载体依然保持较好有序结构。在催化对硝基苯酚还原反应中,经过6 min反应后对硝基苯酚的转化率己达到97.3%,其催化反应性能明显高于单纯氧化铈载体负载的Pt基催化剂。
[Abstract]:Pt based supported catalysts are widely used in various reactions, such as dehydrogenation of low carbon alkanes, oxidation of carbon monoxide, selective oxidation of alcohols, and so on. It is generally believed that the reaction performance of the catalyst is closely related to the distribution of Pt particles on the surface of the catalyst and the structure of the carrier. The Pt catalyst can not effectively control the size and distribution of Pt particles, which can easily lead to the rapid deactivation of the catalyst. Therefore, how to effectively control the dispersity of the metal particles and improve the structure of the carrier in the process of preparing the catalyst is the key to improve the reaction performance of the catalyst. The dispersion of Pt particles and the catalytic reaction are improved in this paper. Homogeneously dispersed Pt nanoparticles were prepared with polyamide amine type (PAMAM) dendrimers as templates and loaded onto mesoporous A1203, mesoporous Ce02 and mesoporous Co3O4-CeO2 carriers. Pt based catalysts with different carrier loads were prepared by heat treatment under specific conditions. A variety of means was used to prepare the catalyst. The prepared materials were characterized and analyzed. The intrinsic structure-activity relationship of the catalyst was discussed with the reduction reaction of p-nitrophenol as a probe reaction and the series characterization results of the catalyst. The hydroxyl terminated polyamide amine type dendrimer was used as the template, the Pt2+ was encapsulated by the coordination reaction, and the sodium borohydride was used as a reductant, and the tree was prepared based on the tree. A uniformly dispersed small size Pt nanoparticle (marked as Pt DENs) of a polymer template was then loaded onto a mesoporous alumina (MA) carrier and a Pt/MA catalyst was prepared. The effect of different calcination atmosphere on the decomposition of the polymer and the effect of calcination temperature on the distribution of Pt particles was studied. The compound can effectively control the agglomeration between Pt particles. At the same time, the roasting at 550 C can not only fully decompose the polymer, but also maintain the smaller particle size of the Pt particles. In the catalytic p-nitrophenol reduction reaction, the catalyst at 550 C shows the best catalytic activity, and the sample is easily recovered and has good repetition. The mesoporous silicon KIT-6 prepared by hydrothermal method, as a hard template, impregnated with cerium nitrate solution, was prepared by roasting and etching, and prepared an ordered mesoporous cerium oxide (meso-CeO2) with a specific surface area of 115.3 m2/g.. The nano cerium oxide material (nano-CeO2) was prepared by the sol-gel method. Then, the PAMAM tree was made. The Pt nanoparticles encapsulated by the polymer are loaded on the ordered mesoporous cerium oxide and the nano ceria carrier, and the two catalysts of Pt/meso-CeO2 and Pt/nano-CeO2 are obtained. The results show that the high specific surface area of meso-CeO2 is beneficial to dispersing Pt nanoparticles, and its regular pore structure can restrict the aggregation of Pt particles, which is beneficial to the maintenance of the particles. The size of Pt particles. In addition, compared with the Pt/nano-CeO2 catalyst, the Pt/meso-CeO2 catalyst shows a higher catalytic activity in the reduction reaction of p-nitrophenol and has a good reuse performance. The mixed solution of cerium nitrate and cobalt nitrate is impregnated to the mesoporous silicon KIT-6, and the ordered mesoporous Co3O4-CeO2 is obtained after roasting and etching. Composite metal oxide Co3O4-CeO2 Pt nanoparticles PAMAM dendrimer encapsulated supported mesoporous Co3O4-CeO2 composite metal oxide carrier, roasting decomposition polymers obtained after Pt/meso-Co3O4-CeO2 catalyst load.Pt nanoparticles to Co3O4-CeO2 composite metal oxide still maintain a small size and good dispersion, and the load In the catalytic p-nitrophenol reduction reaction, the conversion rate of p-nitrophenol has reached 97.3% after 6 min reaction, and its catalytic performance is obviously higher than that of Pt based catalyst supported by pure cerium oxide carrier.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O643.36

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