Preparation And Study Of Precursor Alloy Of Skeletal Ru Catalyst And Its Support

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.