【作者】 王智力；

【导师】 鄢俊敏； 蒋青；

【作者基本信息】 吉林大学 ， 材料学， 2014， 博士

【摘要】 氢气被人们认为是能满足不断增长的高效、清洁的能源需求的最佳载体。氢气在聚合物电解质膜燃料电池(PEM)技术中应用时可以有效地转变为电能。然而，由于氢气具有很低的体积能量密度和质量能量密度，安全、高效地储存和运输氢气成为实现氢能社会的一大挑战。为了解决这一难题，可以使用甲酸作为储氢材料，因为它是无毒的、具有很高的质量能量密度，而且在室温下呈液态，可以安全地储存和运输。更重要的是，甲酸可以通过光催化二氧化碳加氢得到。发展高效和经济的催化剂以进一步提高甲酸的脱氢动力学和热力学性质是应用甲酸作为储氢材料的关键。本论文的研究内容包括以下三个方面：1.目前，所有用于甲酸脱氢反应的固体催化剂都是由贵金属组成的。由于资源稀缺、价格昂贵，这些催化剂不适合大规模实际应用。为了减少贵金属的使用以及进一步提高催化剂的活性，我们引入非贵金属Co与AuPd结构组成CoAuPd合金结构。通过共还原法，在不使用表面活性剂的条件下制备了CoAuPd/C催化剂。由于电子从Co原子转移到Au和Pd原子，CoAuPd/C在室温下对甲酸脱氢反应具有优异的活性和100%的氢气选择性。此外，通过使用DNA功能化氧化石墨烯(GO)并进一步引导CoAuPd纳米粒子(NPs)在DNA-GO表面生长，我们发现，DNA不仅可以有效地控制CoAuPd NPs的生长和分布，而且还能提高CoAuPd/DNA-rGO复合物在水中的分散性。研究结果表明，在室温、没有添加剂的条件下，CoAuPd/DNA-rGO复合物的初始转化频率(TOF)达到85.0mol H2mol催化剂-1h-1，分别是CoAuPd/rGO、CoAuPd NPs和CoAuPd/C的1.9、6.4和2.3倍。另一方面，为了进一步减少贵金属的使用，我们通过共还原法，在不使用表面活性剂的条件下设计和制备了新型的NiAuPd/C催化剂。结果表明，Ni与Au和Pd的合金化改变了催化剂表面的电子结构，使它们在甲酸脱氢反应中的活性得到大幅度提高。2.为了提高催化剂的活性和简化催化剂的制备过程，我们使用柠檬酸(CA)作为分散剂，通过原位合成法制备了Pd/C-CA催化剂并发展了一个高效的甲酸/甲酸钠放氢系统。我们发现，在该系统中，甲酸钠既可以作为氢源又可以作为还原剂，柠檬酸可以极大地提高Pd/C-CA在甲酸脱氢反应中的活性。研究结果表明，在室温下，Pd/C-CA的TOF和转化率在160分钟内可以分别达到64mol H2mol催化剂-1h-1和85%。3.利用氨水作为N源，我们在较低的温度下合成了新型的AuPd-CeO2/N-rGO复合物。我们发现，还原的氧化石墨烯(rGO)中的N原子可以有效地控制AuPd-CeO2纳米复合物(NC)的生长和分布，使得AuPd-CeO2NC具有超细的尺寸和良好的分散性。因此，使用N掺杂石墨烯(N-rGO)可以大幅度提高AuPd-CeO2NC在甲酸脱氢反应中的活性。在室温、没有添加剂的条件下，AuPd-CeO2/N-rGO复合物的初始TOF达到52.9mol H2mol催化剂-1h-1。另外，通过Au3+、Pd2+与GO之间的氧化还原反应，我们发展了一种简易的、绿色的方法合成了Au@Pd/N-mrGO复合物。结果表明，在室温、不使用添加剂的条件下，Au@Pd/N-rGO复合物比它的合金结构和Pd/N-rGO复合物在甲酸脱氢中具有更高的活性，其初始TOF达到89.1mol H2mol催化剂-1h-1。更多还原

【Abstract】 Hydrogen has been considered as one of the best alternative energy carriers to satisfythe increasing demands for an efficient and clean energy supply. Hydrogen can be convertedefficiently to produce electricity when it is combined with polymer electrolyte membrane(PEM) fuel cell technology. However, the safe and efficient storage and transfer of hydrogenis a challenge because of its low volumetric and weight energy densities. To solve thisproblem, formic acid can be used as a material for the storage of hydrogen, because it offershigh energy density, is non-toxic and can be safely handled at room temperature. Moreimportantly, formic acid can be produced from photocatalytic CO2hydrogenation. One of thekeys to the practical application of this system is to develop efficient and economicalcatalysts for further improving the kinetic and thermodynamic properties. In this thesis, themain results are divided into three parts as following:1. All catalysts previously synthesized for the dehydrogenation of formic acid arecomposed of noble metals, hindering their large-scale practical applications due to high costsand scarcity. In order to reduce the usage of noble metals and further improve the activity ofthe catalyst, we introduced non-noble metal Co into AuPd alloys. CoAuPd/C is synthesizedthrough a surfactant-free co-reduction method. Due to the electron transfer from Co atoms toAu and Pd atoms, the CoAuPd/C shows the superior activity and100%hydrogen selectivitytoward hydrogen generation from formic acid at room temperature. In addition, DNA wasused to functionalize graphene oxide (GO) and further to guide the growth of CoAuPd alloynanoparticles (NPs) on DNA-GO surface. We found that DNA can not only efficientlycontrol the growth of CoAuPd NPs, but also promote the good dispersion of theCoAuPd/DNA-rGO composite in water. As a result, the initial turnover frequency (TOF)over the CoAuPd/DNA-rGO composite is measured to be85.0mol H2mol catalyst-1h-1atroom temperature without any additives, which is almost1.9,6.4, and2.3times higher thanthose of CoAuPd/rGO composite, CoAuPd NPs, and CoAuPd/C under the same conditions,respectively. On the other hand, in order to further reduce noble metal usage, we designedand prepared a new catalyst, NiAuPd/C, using a co-reduction method without surfactant. Wefound that alloying of Ni with Au and Pd can modify the catalyst surface, resulting in anenhanced activity for formic acid dehydrogenation. 2. In order to improve the activity of atalyst and simplify the catalyst preparationprocesses, we developed the highly efficient hydrogen generation from formic acid/sodiumformate aqueous solution catalyzed by in situ synthesized Pd/C with citric acid. We foundthat sodium formate plays the role of both reducing agent and hydrogen source in our systemand citric acid can dramatically improve the activity of Pd/C for the dehydrogenation offormic acid. As a result, the conversion and TOF for decomposition of formic acid/sodiumformate system can reach the highest values ever reported of85%within160min and64mol H2mol catalyst-1h-1, respectively, at room temperature.3. Using ammonia solution as the N source, we successfully prepared a new N-dopedgraphene based catalyst, AuPd-CeO2/N-rGO hybrid at low temperature. We found that theincorporation of N atoms into reduced graphene oxide (rGO) is the key to the formation ofthe ultrafine and well-dispersed AuPd-CeO2nanocomposites (NC). As a result, theapplication of N-rGO dramatically improves the activity of AuPd-CeO2NC for hydrogengeneration from formic acid. The intial TOF over AuPd-CeO2/N-rGO hybrid is measured tobe52.9mol H2mol catalyst-1h-1without any additives at298K. On the other hand, wedevelop a green and facile sequential reduction route to prepare Au@Pd core-shell NPsgrowing on nitrogen-doped reduced graphene oxide (Au@Pd/N-rGO) by redox reactionsbetween Au3+, Pd2+and GO. As a result, the Au@Pd/N-rGO hybrid shows much higheractivity for formic acid dehydrogenation than that of the AuPd alloy nanoparticles/N-rGOand Pd/N-rGO hybrid. Its initial TOF is89.1mol H2mol catalyst-1h-1at room temperaturewithout any additives.更多还原