负载型Pd基双金属纳米粒子的合成及其催化还原六价铬

发布时间：2018-03-21 16:05

本文选题：六价铬　切入点：Pd　出处：《武汉纺织大学》2017年硕士论文　论文类型：学位论文

【摘要】：六价铬(Cr(VI))是常见的水污染源之一,具有高环境毒性及致癌性;而三价铬(Cr(III))低毒且可转为氢氧化铬沉淀,易从水体中分离。在合适的催化条件下,利用甲酸将Cr(VI)还原为Cr(III)是处理铬污染的有效方法之一。本论文通过液相法合成了两种炭负载的纳米金属催化剂,探索了其将Cr(VI)还原转化为Cr(III)的催化活性和催化机理。首先,以水合肼为还原剂、采用一步水热还原法制备了氮掺杂石墨烯(NG)负载的CuPd纳米合金(PdCu/NG),并利用XRD、HRTEM、EDX、ICP-OES和XPS等手段对材料的物相、结构、组成和表面化学态等进行了详细表征。结果表明,NG表面上负载的纳米金属为均相的PdCu合金(而非常见的Cu和Pd两相混合物),金属的负载量为35 wt.%,平均粒径为4.7 nm。该PdCu/NG催化剂对甲酸还原Cr(VI)具有优异的催化活性,催化反应速率高达0.406 min-1,活化能低至34.9 kJ/mol。优异的催化活性来源于金属-载体强相互作用(SMSI)效应,以及PdCu金属间的协同效应。相比于常见的贵金属催化剂(如Pd、Pt等),所合成的PdCu/NG具有价格低廉、活性更高等优点。其次,将金属有机框架化合物ZIF-8炭化后得到的ZC作为载体,水合肼为还原剂,合成了ZC负载的NiPd双金属纳米催化剂(NiPd/ZC)。并利用XRD、HRTEM、EDX、ICP-OES和XPS等手段对其进行了表征。研究发现,炭化后的载体保持着多孔炭骨架空间结构,NiPd双金属纳米颗粒均匀地负载在ZC介孔内。ZC上负载的纳米金属为双相Ni Pd纳米粒子。在催化还原Cr(VI)的实验中,NiPd/ZC双金属催化剂的催化活性明显优于单金属纳米催化剂。其催化速率高达0.396 min-1,活化能低至28.7 kJ/mol。经过五次循环使用后,催化剂的催化活性只降低了2.7%。相比较PdCu/NG催化剂,ZC具有更大的比表面积和独特的空间框架结构,使得金属粒子的附着位点增多,催化稳定性更好。磁性Ni粒子的引入,让催化剂的回收再使用变的更加方便。最后,总结全文并展望了课题未来研究方向。
[Abstract]:Hexavalent chromium (Cr) is one of the most common sources of water pollution, with high environmental toxicity and carcinogenicity, while the trivalent chromium (Cr) is low toxic and can be converted to chromium hydroxide precipitation, which is easily separated from water. In this paper, two kinds of carbon supported nanometallic catalysts were synthesized by liquid phase method, and their catalytic activity and catalytic mechanism were explored. Using hydrazine hydrate as reducing agent, a nitrogen-doped graphene (NGN) supported CuPd nanoalloy PdCu / NGN was prepared by a one-step hydrothermal reduction method. The phase and structure of the material were analyzed by means of XRDX HRTEMU EDXICP-OES and XPS. The composition and surface chemical state were characterized in detail. The results show that the nanometallic loaded on the surface of NG is a homogeneous PdCu alloy (not a common Cu and PD two-phase mixture). The metal loading amount is 35wt. and the average particle size is 4.7 nm. The PdCu/NG catalyst has excellent catalytic activity for the reduction of CrVI by formic acid. The catalytic reaction rate is as high as 0.406 min-1, and the activation energy is as low as 34.9 kJ / mol. The excellent catalytic activity comes from the strong metal-carrier interaction (SMSI) effect. Compared with the common noble metal catalysts (such as PD Pt etc.), the synthesized PdCu/NG has the advantages of low cost and higher activity. Secondly, the ZC obtained from the carbonization of the organometallic framework compound ZIF-8 is used as the carrier. The ZC-supported NiPd bimetallic catalyst, NiPD / ZCX, was synthesized by hydrazine hydrate as a reductant. It was characterized by XRDD-HRTEMN EDX ICP-OES and XPS. The carbonized carrier maintained the porous carbon skeleton space structure and the nanometallic particles loaded uniformly on ZC mesoporous. ZC were biphasic NiPd nanoparticles. In the experiment of catalytic reduction of CrVI, NiPd / ZC bimetallic catalyst was used. The catalytic activity of the catalyst is obviously better than that of the monometallic nanometer catalyst. The catalytic rate is up to 0.396 min-1, and the activation energy is as low as 28.7 KJ / mol. Compared with the PdCu/NG catalyst ZC has a larger specific surface area and a unique spatial frame structure, which makes the metal particles have more adhesion sites and better catalytic stability. It is more convenient to recycle and reuse the catalyst. Finally, the paper summarizes the whole paper and looks forward to the future research direction.
【学位授予单位】：武汉纺织大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X52;O643.36

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