The Study Of Transition Metal Oxide Nano- Mesoporous Material In Oxidative Dehydrogenation Of Propane To Propylene

Propane is an inactive alkane, which is abundant in natural gas, light hydrocarbon oil and refinery gas. Propane selective oxidation is promoting the use of abundant natural gas resources in alternative way of chemical production of petroleum products, which has an extremely important in the natural gas industry significance. Currently, many researchers have carried out extensive study about propane oxidative dehydrogenation, and series of catalysts were prepared, all of these developed the application and chemical reaction engineering theory. The PODH reaction is an exothermic reaction which can carry out at lower temperature, and is thermodynamically easy and can greatly reduce energy consumption, but the deep oxidation reaction of propane is easy to take place and generate the byproducts of oxo-products and CO, CO2, etc.. The catalysts applied in PODH reaction are still in the research stage, and the practical application of the catalysts remains to be further studied. Thus, the research of the active site in propane oxidative dehydrogenation and the impact factors of different reaction passway (the deep oxidation or selective oxidative reaction) in propane oxidative dehydrogenation are necessary and important to guide the development of high activity and propene selectivity catalysts.This paper carried out the study of nanocrystal catalysts and mesoporous catalysts for the oxidative dehydrogenation of propane used the transition metals (V, Mo, Mn, Cu, Cr, W) which could activate propane as the main active species. The properties of bulk/surface, crystal structure, active species distribution and valence state, surface acidity and oxygen species on the surface of catalysts were extensively characterized and analyzed. The relationship between the active sites and performance was explained preliminary. The detailed chapter contents are as follow:The first chapter analyzes the research status and application of propane oxidation to propylene and gives the research meanings. The different characteristics of active species in the catalytic reaction are summarized in detail. The problems and limitations which are necessary to study further in this project are pointed out.The second chapter describes the experimental reagents, test methods and catalyst characterization techniques used in this paper.In the third chapter, we successfully synthesized a series of Zr-M (M=V, Mo, Fe, Mn, Mg, Nb) nano-crystalline catalysts in the use of hydrothermal synthesis method which could good disperse the active component. In this section, different elements were chosen to dope in the catalysts and applied in oxidative dehydrogenation of propane. And the different catalysts gave different catalytic activity, in which the Zr-V system catalysts got the highest propylene yield of 21.3%. The redox capability of the catalysts, the catalyst surface acidity (acidic type and the generation reasons of Bronsted acid) as well as the relationship between them and the performance of the catalysts were studied.In the fourth chapter, mesoporous Mn2O3 was successfully synthesized by hard template method. A series of catalysts loaded of V, Mo and Cu elements on meso-Mn2O3 were applied in PODH reaction and showed different catalytic performance. The reaction paths of the oxidation reaction on the catalyst surface were studied by in situ infrared experiments used propane and propene as probe molecules. The changes of the acid properties on the catalysts surface and oxygen species were analyzed by in situ IR and XPS experiments. In the result, we found that the catalytic performance (including catalytic reaction path) is closely related with the acidic properties and the oxygen species on the catalyst surface, which clarified preliminary that different element oxides and the surface oxygen species (variety, distribution and activities) can induce different reaction paths (deep oxidation and selective oxidative reaction) in the propane oxidation reaction.In the fifth chapter, we studied the performance of the catalysts of W/MgO and M-W/MgO in PODH reaction. The aggregation of active species and oxygen species on the surface were preliminary studied by Raman, UV-visible and CO2-TPD experiments. But there are still some problems to be solved in the next lab work, such as the role played by W in the interpolation of oxygen, the amount of the loadings, the impact of surface oxygen species and the acid properties for reaction pathway.