Mesoporous Transition Metal Oxides And Porous-supported Metal Oxides Catalytic Activation Of Methane

At current usage, worldwide reserves of petroleum and coal are projected to only last for a few decades. This situation is a serious problem on a global level.Developin g efficient strategies for the selective activation and transformation of methane as the most abundant feedstock for organic chemicals to value-added chemicals or liquid fuels would provide a promising alternative for easing up the coal and oil-demanding situation during the high-growth process of the economic and the rapid development of science and technology. However, the bonds to be broken are thermodynamically strong and kinetically inert. Construction of the more sophisticated value-added architectures via C-H bond activation in methane is a highly difficult task.Although methane conversion has been investigated for one hundred years, only indirect conversion method has realized in industrial scale. The development of direct conversion of methane to useful chemicals by activating C-H bonds still remains a difficult task despite thousands of Catalysts and almost all elements except group zero elements in periodical table used in the past decades.The investigation for new ways of methane conversion and the inherent laws of methane conversion is very important to solve the energy, resources and environmental problems in the sustainable development of humane society.In addition to with the composition of the transition metal oxides and the usual physical and chemical properties, mesoporous transition metal oxides possess a large aperture, large surface area, diverse surface structures, nanoparticle properties and function of micro-reactor. Moreover, their pore structure and composition can be tunable. By comparison with the known methane conversion catalyst, mesoporous transition metal oxide materials exhibit a lot of unusual characters and may provide a great deal of opportunity to find the excellent catalysts for breaking the C-H bonds to establish the new C-C, C-O. In this thesis, the research effort has focused on the preparation of mesoporous transition metal oxide and activation of methane by mesoporous transition metal oxide as catalyst. The main points of the thesis are as follows.(1) A novel mesoporous α-Fe2O3material have been prepared by using the ionic liquid as the media, acetylacetone iron as the iron source and diphenyl ether as the morphology control reagent. It is found that the material has a flower-like structure by SEM, each nanorod of about567nm, the width of52nm. It is also characterized by TEM, and found there are mesopores in the the nanorod, the pore diameter is3.2nm. The BET showed that the novel material has a specific surface area of55.1m2·g-1. Carried out the catalytic activation of methane experiments, at3atm, CH4/O2=3, GHSV=4800ml/g-h, the results show the lowest temperature of breaking C-H bond of methane is130℃over this Mesoporous α-Fe2O3nanorods catalyst. The reason is mesoporous α-Fe2O3surface adsorption of oxygen and interstitial oxygen plays an important part in the methane activation(2) Three-dimensional mesoporous CO3O4and doped with other transition metal and rare earth metal (Ce) material have been prepared by using improved hard template methods. Activation methane experiment were carried out over these CO3O4materials, and found mesoporous Co3O4catalyst can activate methane at145℃, compared to bulk Co3O4,the activation temperature is lower30℃, which is lower71℃than the lowest temperature in the literature. While using the mesoporous Co3O4doped with chromium(5%Cr-Co3O4) it can help break C-H bond of methane and build C-O bond at130℃, the selectivity of CO is higher than90%, and the catalyst has long life. It is promising that the material can be used as syngas catalyst.(3) Mesoporous NiO and doped with other transition metal and rare earth metal (Ce) material have been prepared by using improved hard template methods. Activation methane experiment were carried out over these NiO materials, and found mesoporous NiO catalyst can activate methane at210℃, compared to bulk NiO, the activation temperature is lower70℃, While using the mesoporous NiO doped with iron (5%Fe-NiO) it can help break C-H bond of methane and build C-O bond at130℃, which is lower86℃than the lowest temperature in the literature. The selectivity of CO2is higher than90%at250℃, and the catalyst has long life. It is promising that the material can be used as methane combustion catalyst.(4) Synthesis of the two-dimensional mesoporous TiO2and doped transition and rare earth metal oxide (Ce) catalysts have been completed by using acid-base self-regulating method. Activation methane experiment were carried out over these TiO2catalyst, we can found that the mesoporous TiO2can activate methane at210℃, compared to bulk TiO2,the activation temperature is lower290℃. The5%Ce-TiO2catalyst can activate methane at140℃, which is lower76℃than the lowest temperature in the literature. The XPS results confirmed the type of catalyst the reason is mainly chemical adsorbed oxygen from the catalytic oxidation at low react temperature, while and lattice oxygen plays an important part in high react temperature.(5) In order to further understand the rule of pore and pore structure in the catalytic conversion of methane, we prepared non-porous quartz sand, and mesoporous molecular sieve KIT-6, microporous zeolite HZSM-5supported transition metal oxides and rare earth metal Ln (Ln=La and Ce, and Gd) catalyst by impregnation method, and studied the behavior of the catalytic activation respectively. According to the experiment results, the activation temperature in non-porous quartz sand supported is the highest (670℃). Methane activation temperature over KIT-6supported metal catalyst is550℃, while the HZSM-5supported transition metal oxides and rare earth metal can activate methane at350℃. At low temperature of723K, methane can be easily activated in the presence of ethylene in the feed, and converted to higher hydrocarbons (C2-C4) and aromatics (C6-C10), through its reaction over rare metals modified Zn/HZSM-5zeolite catalysts. Methane can get37.3%conversion over the above catalysts, the catalysts show a longer lifetime than usual metal supported HZSM-5zeolite catalysts without adding any rare earth metals.In conclusions, these results indicated the pore and porous structure in mesoporous transition metal oxides play a important role in the activate methane and can significantly improve the catalytic activity of mesoporous transition metal oxides under low temperature. Mesoporous transition metal oxides may be a promising catalytic material in the large-scale production of the fine chemicals.