【作者】 白富栋；

【导师】 李廷举； 吕连海；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2011， 博士

【摘要】 催化剂在化学反应中起着非常重要的作用。骨架金属作为一类重要的催化剂已被人们广泛认识,它的制备过程是先将铝与活性金属熔炼得到合金,然后用碱液活化浸出其中的铝,得到的具有海绵状结构的活性金属就是骨架金属催化剂。其中,骨架镍催化剂的制备和研究是最早也是最多的,很多材料制备技术如机械合金化、快速凝固技术等被用到了铝镍母合金的制备上,不同的制备技术会对母合金的结构产生影响,从而影响最终骨架镍催化剂的性能。骨架钌是一类高度活泼的加氢催化剂,它能够在较低温度和较低压力下,催化多种不饱和键的加氢反应,在医药、精细化学品等许多高经济附加值产品工业领域具有十分广阔的应用前景。但是由于金属钌价格昂贵、熔点高,制备骨架钌催化剂母合金(铝钌合金)比较困难,文献报导主要集中于骨架钌催化剂在加氢反应中的应用方面,而对铝钌合金具体的制备方法以及不同的制备过程对铝钌母合金结构的影响却鲜有报导。另一方面,骨架钉催化剂母合金中钉的含量一般在50Wt%左右,与负载型催化剂相比,骨架钌催化剂的成本太高,能否找到合适的途径来降低其成本,直接关系到骨架钌催化剂能否推广应用。本文主要以铝钌合金为研究对象,但由于钌是贵金属,所以在工艺探索过程中会用铝镍合金作为替代物进行分析考察。首先采用高频感应熔炼和机械合金化以及后续热处理的方法制备了铝钌合金,考察了制备工艺对合金相组成的影响。然后,结合本实验室的优势,将电磁搅拌技术引入到了铝镍合金的制备过程中,通过变化磁场强度来改变铝镍合金的晶粒尺寸,考察能否获得只有晶粒尺寸单一因素变化的母合金锭,为深入研究母合金结构与对应催化剂结构和活性的构效关系提供基础。最后考察了几种添加载体的方法,以期来降低骨架金属催化剂的成本。取得的主要研究成果如下：由高频感应熔炼得到的铝钌合金(50wt% Ru)中主要存在Al13Ru4和Al2Ru两相。对对烷基苯甲酸加氢实验结果表明,由水淬后的铝钌合金制得的骨架钌催化剂具有更高的活性。相对于随炉冷却的试样,水淬后的试样中的Al2Ru相含量更高,而且晶粒尺寸也有变小趋势,这可能是其具有更高活性的原因之一。在高频感应熔炼过程中向铝钌合金中引入镍进行改性后,合金中除了Al3Ni2相外,其他为铝镍钌三元合金相,继续添加石墨粉热处理后混合粉中的合金相变为Al2Ru和铝镍钌三元合金相。Al-Ru-Ni-C合金粉经NaOH浸取活化后制得的骨架钌镍碳催化剂用于对硝基苯甲醚的加氢反应制备对氨基苯甲醚,使用寿命超过63小时,反应温度低于100℃,目的产物的选择性高达99.4%,这可以归因于催化剂中骨架钌和骨架钌镍两种共存结构的配合以及石墨的分散和稳定作用。以纯铝粉和钌粉为原料通过机械合金化球磨20、30和50小时后并没有直接得到铝钌金属间化合物,而是得到亚稳的Ru(Al)过饱和固溶体,经过550℃和700℃热处理后Ru(Al)过饱和固溶体完全转变为铝钌金属间化合物。此过程大大降低了生成铝钌金属问化合物的温度,最低相转变温度为394.3℃。研究结果表明工艺控制剂乙醇参与了机械合金化进程,热处理时消耗了一部分铝,使得最终合金成分发生变化,致使Al5Ru2相意外地出现在热处理后的样品中。本实验条件下制得的Al5Ru2在550℃下可以稳定存在,而在700℃下分解而消失。由于文献中对此相的稳定性存在争议,为了进一步验证Al5Ru2的存在不是由乙醇造成的,采用电弧熔炼制备了铝钌成分在5：2附近(原子百分比)的合金。结果表明,在成分允许的条件下,Al5Ru2可以在激冷条件下与Al13Ru4、Al2Ru竞争形核长大而出现,也可以在凝固速度缓慢的条件下由液相与Al2Ru相包晶反应而得到。将电磁场引入到了骨架金属催化剂母合金的制备过程中。研究结果表明,施加80A和140A电磁搅拌后铝镍合金中较大的Al3Ni2树枝晶消失,变为细小的等轴晶,Al3Ni2相的平均尺寸由64.5μm变为37.2μm和35.5μm。而且合金中Al3Ni2相含量略有减少,而Al3Ni相含量略有增加。这主要是由于电磁搅拌过程中,Al3Ni2枝晶被打碎,增加了Al3Ni2相与液相的接触机会,有利于生成Al3Ni的包晶反应的进行。加氢活性测试结果表明,由施加电磁搅拌后得到的铝镍合金制备出的骨架镍催化剂具有更高的催化活性。为降低骨架贵金属催化剂的成本,我们首先考虑了添加载体来负载母合金的工艺。实验结果表明,直接将合金粉与无机微粉混合进行高温处理并不能使合金有效分散于无机微粉上,而且在高温条件下合金粉容易被氧化而转变为尖晶石结构。采用特殊的磁控溅射设备可以将铝钌合金镀在SiC、MgO、SiO2微粉和空心微球上,但这种方法对设备要求较高,制备周期长,产量低。通过分析铝镍合金中Al3Ni和Al3Ni2相的活化过程以及对比常规纳米金属粒子的制备方法,我们指出制备骨架金属催化剂的过程实际上就是制备具有特殊结构纳米金属催化剂的过程。常规浸取活化方法制得的骨架金属催化剂是母合金活化过程中产生的一次纳米金属粒子聚集长大后的产物,通过添加载体可以防止纳米金属粒子的团聚,选择合适的载体将可以制备出廉价的负载型骨架金属催化剂。提出了向铝镍合金粉中添加拟薄水铝石来降低成本的方法,采用5-6%的硝酸溶液进行胶溶,热处理适宜温度为550℃,可以得到γ-Al2O3结合铝镍合金的混合粉,活化结果显示,γ-Al2O3的存在不会阻碍活化过程的进行,而且活化出的纳米镍粒子可以有效地分散在}-Al2O3载体上。更多还原

【Abstract】 Catalysts play a very important role in chemical reactions. Skeletal metal have been well known as a kind of important catalyst. It can be obtained by alkali leaching the alloy of Al and the active metal. When Al is removed from the alloy, the left active metal with a sponge like structure can be used as skeletal metal catalyst. Skeletal Ni catalyst has been used and studied for a long time. Many materials production processes such as mechanical alloying, rapid solidification are used to produce the precursor alloys. Different production process has a very important influence on the alloy structure which finally affects the performance of skeletal Ni catalyst.Skeletal Ru is a kind of catalyst with high activity for hydrogenation. It can be used for hydrogenation of unsaturated bonds under very mild conditions. And it has a very wide application prospect in the production of high value added medicine, fine chemicals. However, skeletal Ru catalyst can not be widely used because ruthenium is a noble metal. Moreover, ruthenium has a high melting point which makes the production of precursor Al-Ru alloy difficult. Previous reports mainly concerned about the application of skeletal Ru catalyst and had very few reports on the details of the production of Al-Ru alloy and the relationship between the production process and the alloy structure. Compared with supported catalysts, precursor alloy of skeletal Ru catalyst is too expensive since it has a very high content of ruthenium (50wt%). Therefore, a method which can cut the cost of skeletal metal catalyst is urgently needed for its application in industry.Al-Ru alloy is the main research subject in this dissertation. Al-Ni alloy is used as a substitution for Al-Ru alloy in the process of technical investigation because Ru is too expensive. The first part is about the production of Al-Ru alloy by high frequency induction melting and mechanical alloying with subsequent heat treatment, and the influence of preparation process on phase composition was studied. In the second part, rotating magnetic field (RMF) is introduced in the production process of Al-Ni precursor alloy of skeletal Ni catalyst to study the influence of RMF on the microstructure and phase content of Al-Ni alloy, because it is well known that the alloy grain size can be effectively refined when electromagnetic field (EMF) is introduced in the solidification process. Therefore, it is interesting to investigate whether the introduction of EMF in the solidification of Al-Ni alloy can only change the grain size or not. The last part is about several exploratory experiments in which support is added to reduce the cost of skeletal metal catalysts. Main research details and results are as follows.The Al-Ru alloy with 50 wt% Ru produced by high frequency induction melting contains two main phase:Al13Ru4 and Al2Ru. When the melt was quenched by water, the content of Al2Ru increased, and its grain size decreased. Skeletal Ru catalyst obtained from quenched samples shows higher hydrogenation activity. Al-Ni-Ru alloy with 50 wt% Ni and 50 wt% Ru was produced by the same method, and it contains Al3Ni2 and several ternary phases. When graphite powder was added into the Al-Ni-Ru alloy powder and heat treated at high temperature, the phases transformed to Al2Ru and several ternary phases. The skeletal Ru-Ni-C produced by leaching Al-Ru-Ni-C powder shows very high activity in the hydrogenation of p-nitroanisole to produce p-aminoanisole. It could be used for more than 63 hrs at temperature lower than 100℃and the selectivity for desired product was higher than 99.4%. It can be attributed to the synergy of skeletal Ru and skeletal Ru-Ni and the dispersion of graphite.Metastable Ru(Al) solid solution was the only phase obtained after milling elemental Al and Ru powders (50wt% Ru) for 20,30 and 50 hours. It transformed to Al-Ru intermetallics after heat treatment at 550℃and 700℃. Al5Ru2 phase was appeared accidentally in the samples. The results showed that the process control agent ethanol participated in alloying and consumed part of aluminium which finally changed the alloy composition. Al5Ru2 phase is stable at 550℃and disappear at 700℃. The lowest phase transformation temperature is 394.3℃, which is very low compared with that in metallurgy production process. To clarify the controversy in the references and verify that the appearance of Al5Ru2 was not induced by ethanol, Al-Ru alloys with almost the same composition of Al5Ru2 was produced by arc melting. It showed that Al5Ru2 can be obtained not only via competitively nucleation with Al13Ru4 and Al2Ru and growing under rapid solidification circumstance but also via peritectic reaction of fluid and Al2Ru under low solidification circumstance.Rotating magnetic field (RMF) was introduced in the production process of Al-Ni precursor alloy of skeletal Ni catalyst. The results showed that the big dendrites of Al3Ni2 disappeared, the size of Al3Ni2 decreased from 64.5μm to 37.2 and 35.5μm, phase content of Al3Ni2 decreased while Al3Ni increased after applying field current of 80A and 140 A, respectively. The change of phase content is probably caused by the increase of surface area between the Al3Ni2 phase and fluid which is favorable to the peritectic reaction. Skeletal Ni catalysts obtained from samples with RMF showed higher hydrogenation activity.As to the methods to reduce the cost of skeletal metal catalysts, we first thought about adding support to carry precursor alloy. The results showed that the alloy powder was not effectively dispersed on inorganic micro powder by heat treating the mixture of both powders and it can be readily oxidized and transformed to spinel at high temperature. Then we plated Al-Ru alloy on the surface of SiC, MgO, SiO2 micro powder and cenosphere particles using a special magnetron sputtering equipment, but this method has several disadvantages, like highly requirement on equipment, long production period and low outcome.By analyzing the leaching process of Al3Ni and Al3Ni2 and comparing the conventional production of nano metal particles, we conclude that the production process of raney metal catalyst is a production process of nano metal particles with special structure. The skeletal metal catalyst obtained by conventional leaching process is a product after the aggregation of the first nano metal particles obtained by leaching. Adding support can prevent the aggregation of the first nano metal particles, and cheap supported metal catalyst can be produced by choosing an appropriate support. Therefore, we proposed a method to produceγ-Al2O3 supported skeletal Ni catalyst. The mixture of Al-Ni alloy powder and pseudo-boehmite was first peptized using 5-6% HNO3 and then it was heat treated at 550℃. Pseudo-boehmite transformed toγ-Al2O3. The results showed that the presence ofγ-Al2O3 would not hinder the leaching process and nano Ni particles produced in the leaching process can be effectively dispersed onγ-Al2O3.更多还原