Application Of Novel Supported Chromium Oxide Catalysts In Propane Oxidative Dehydrogenation

The development of human society has long been depended on coal, oil, natural gas, where oil accounts for the first place. In recent years, with the increasing depletion of oil resources, it is of great interest to implement natural gas as raw material to replace part of the traditional petroleum-based projects, so as to alleviate the current pressure on oil consumption. Natural gas resource is abundant in China, which provides a good platform for the research based on natural gas.Propane is one of the most important components of natural gas. Using propane to produce propylene can not only reduce the current dependence of propylene production on oil industry, but also meets the rising social demand for propylene, which is worthful for both industrial application and theory research. Currently industrial installations are propane dehydrogenation to propylene without oxygen process device, which shall be carried out under high temperature, and the catalysts get coked and deactivation quickly. In order to reduce the reaction temperature and extend the life of the catalyst, oxidative dehydrogenation of propane is an ideal process. Unfortunately, reports of propane oxidative dehydrogenation are still unsatisfying, and there is no catalyst that meets the industrial application standards until now. Moreover, the activation pathway of propane on different catalysts, the nature of the active sites remains unclear.In this article, chromium which has been shown to effectively activate propane, was chosen as the active species on different carriers and tested in propane oxidative dehydrogenation. Research carried out with chromium species supported on ordinary powder, high specific surface area mesoporous materials, carbon nanotubes were processed. Features on the properties of bulk/surface, crystal structure, chromium distribution and valence state were extensively characterized and analyzed to give the structure-activity relationship. The detailed chapter contents are as follow:The first chapter analyzes the research status of oxidative dehydrogenation of propane and gives the research meaning. Chromium catalysts in propane oxidative dehydrogenation are summarized in detail, and the problems and limitations in this project are pointed out.The second chapter of this thesis tells the chemicals source, experimental method and the catalyst characterization details.The third chapter studies the catalytic performance of mesoporus TiO2incorporated with chromium catalyst. One step surfactant induced self-assembly method was adapted, and a propylene yield of over20%was obtained, which is superior to that of ordinary Cr-TiO2catalyst. Through an integrated characterization and analysis of the catalysts, the high propylene yield was associated with the characteristic interaction of titanium with chromium, beneficial effect of the mesoporous structure, which makes the surface with homogeneous distribution of active chromium species.The fourth chapter talks about chromium supported on alkaline nano MgO. Chromium crystalline phases as formed on MgO were emphatically analyzed. The redox, acid-basic properties of different chromium phases, as well as the relationship between chromium phase and catalytic activity were also explored.The fifth chapter introduces the situation of multi-walled carbon nanotubes loaded with small amounts of chromium catalyst, which got higher than80%propylene selectivity at nearly20%of propane conversion. The synergistic effect between chromium and CNT was revealed. The sixth chapter talks about the application of mesoporous silica (MCF) loaded chromium catalyst and it was illustrated that potassium greatly improves propylene selectivity. Through preliminary characterization, the optimization effect may be that incorporation of K resulted in a dispersion of Cr(VI) species predominate on the surface. This chapter also compares nearly ten different carrier loaded chromium catalysts and it was discovered that the property of the carrier, specific surface area, channel structure, surface groups, chromium species distribution have great influence on catalytic activity.