Synthesis Of Several Mesoscopic Materials And Their Properties

It is known that the catalytic properties of a material are sensitive not only to its size but also to the shape of morphology. Using the bottom-up synthetic approach in solution, the size and morphology of nano-materials can now be controlled effectively,and therefore, the multilevel structure, the crystal facet growth, and the unique metal-oxide interfaces can be artificially created and modified. In such a way, the structure-performance relationship of the target materials can be elaborated in depth.The related field is becoming a hot spot in controlling the structure and performance of various functional materials.CO is recognized as one of the key air pollutants. The catalytic oxidation of CO has attracted considerable attention because of its wide application in CO detectors,closed-cycle CO2 lasers and petrochemical industry. In addition, CO oxidation is often used as a model reaction to study the catalytic properties of other complete oxidation catalysts. Catalytic CO oxidation has become a hot topic in the current catalysis chemistry worldwide. The research and development of an efficient yet stable CO oxidation catalyst is of practical and theoretical significance.Partial oxidation of methane (POM) is an important topic in the ulitzation of natural gas. Partial oxidation of methane is considered as the most promising approach to producing syngas from methane. Curently the syngas production from methane via POM reaction is mostly performed on the Ni-based catalysts. However,the Ni-based catalysts were found to be easily oxidized and deactivated in the POM reaction, and in addition, the sintering and coking of Ni component are the major issues to be sloved for practical application. In order to improve the stability of Ni-based catalyst, the core-shell type catalyst in which the Ni core particles can be fine tunable were developed. Not only the activity but also the durability of the Ni based catalyst has been obviously enhanced. It was observed that introduction of small amount of noble metals such as Pt, Ru, Rh to Ni can suppress Ni oxidation meanwhile promote methane conversion. Therefore, it is highly desireable to develop the core-shell catalyst with the bimetallic cores for the POM reaction, and to establish the corresponding composition-structure-performance relationship.In the family of mesoporous materials, SBA-15 has high surface area, uniform pore size distribution, and thicker pore walls. It is generally synthesized under strong acidic conditions by employing mineral acids. However, the SBA-15 materials consisting of pure-silica frameworks are of limited use in practical applications due to the lack of acid sites. Synthesis of SBA-15 material in the absence of mineral acid and simultaneous introduction of other metal ions in the framework of SBA-15 is of great importance for acid-catalyzed application.Based on the above understandings, several mesoscopic materials of hierarchical structures have been prepared and the related structure-performance relationships systematically investigated, the main conclusions are as follows:(1) A novel synthetic strategy has been adopted to deposit Au nanoparticles (NPs)(ca. 5 nm) on a hollow FeO, substrate using Au/?-FeOOH hybrid nanocrystals as the precursor. The derived Au/ FeOx hollow composite shows a substantial pretreatment effect on CO oxidation: with a pretreatment in the reaction feed at 180? for 0.5 h,the hollow Au/FeOx shows the T 100 of CO oxidation decreasing from 180 to 88?. O2 temperature-programmed desorption and X-ray photoelectron spectroscopy characterizations revealed that the pretreatment may result in (?) the creation of electron holes in the p-type FeOx substrate and electron deficiency of Au nanoparticles as well as a strong Au-FeOx interaction; (?) appropriate coverage of oxygen adspecies on the Au NPs; and (?)increased surface oxygen density,especially at the Au-FeOx boundary region, as a result of the spillover effect of oxygen adspecies from Au NPs. All of these features are responsible for an overall enhanced activity of CO oxidation and better durability of the Au/FeOx hollow composite.(2) Three Co3O4 nanostructures of different morphologies (nanocube, nanoplate,and nanobelt) were synthesized via hydrothermal and precursor calcination methods.HRTEM study indicated there are different exposed crystal facets on these Co3O4 nanostructures. The O2-TPD investigation further revealed that there are oxygen adspecies in different concentration and binding strength on the corresponding Co3O4 nanostructures. Because of the specific exposed crystal facets and different structure regularity of Co3O4 nanostructures, the surface atoms arrangement and active sites constitution and density could be largely modified, which in turn affected the catalytic activities of three distinctive Co3O4 nanostructures in CO oxidation: nanoplates >nanobelts > nanocubes. Through deposition of Au nanoparticles on the Co3O4 nanostructures, specific Au- Co3O4 interfaces can be obtained and they also showed obvious difference in CO oxidation activity. The results demonstrated the importance of both Au nanoparticles and Co3O4 substrate surfaces, especially the boundary region between the two, for the target reaction.(3) The nanostructures of nRu-Ni@SiO2 (n = 0.01-0.1) were synthesized for the POM reaction. Even low content of Ru showed significant impact on the catalytic performance. Superior performance can be achieved when the Ru/Ni atomic ratio of 0.01-0.06is adopted. The well-dispersed Ru species on Ni nanoparticles can more efficiently promote the POM reaction. The effects of reaction temperature and space velocity on catalytic performance were investigated, and the optimized temperature and space velocity were found to be 700? and 72,000 ml g-1 h-1 respectively.(4) The Fe-incorporated mesoporous SBA-15 materials with the Fe content up to a Fe/Si molar ratio = 0.05 were synthesized via pre-hydrolysis of TEOS employing P123 triblock copolymer as the template. The synthetic strategy is that hydrolysis of Fe salt precursor can provide acidic medium essential for the pre-hydrolysis of TEOS.Different Fe/Si ratios and TEOS pre-hydrolysis periods were employed to modify the structure and texture of the Fe-incorporated SBA-15. The impact of Fe sources (ferric nitrate, ferric chloride, and ferric sulfate) on the characteristics of Fe-SBA-15 has also been investigated. Ferric nitrate showed the best effect among the three Fe sources.Pyridine adsorption IR study demonstrates enhancement in Br(?)nsted and Lewis acidity of as-synthesized Fe-SBA-15 materials. Moreover, the employed treatments(700? for 10 h in air and 600? for 3 h in 100% steam) verified good thermal and hydrothermal stability of the derived Fe-SBA-15. The present methodology also seems versatile to synthesize other metal-substituted SBA-15, such as Al- and Cr-SBA-15.