C1Chemistry:Studies On Methane Reforming With Carbon Dioxide To Syngas And Methanol To Olefin

In recent years, the development of material science has provided abundant academic thoughts and technical tools for the research of catalysts and catalytic processes, with the design, synthesis and catalytic properties of nano catalyst as the developing trend of catalytic science. Novel nanomaterials are usually designed for specific heterogeneous catalytic processes and their catalytic performances are studied after assembling or modification. Natural gas is an important energy source for human activities, and the effective use of natural gas has become particularly important as the growing tension of fossil energy reserves. Therefore it is necessary to study the conversion and utilization of traditional energy resources in conventional catalytic processes, aimed at improving efficiency and reducing emissions. The research in our thesis is focused on the conversion and utilization of natural gas in conventional catalytic reactions, e.g., the key points of the catalyst stability for methane reforming with carbon dioxide, the reaction route of MTO process and the effect of catalyst polarity for relative reactions. Nanomaterials are designed, synthesized and modified for specific reactions, in order to improve the reactivity, product selectivity and catalyst stability, and further elaborate the reaction mechanisms.1. Reforming of methane to syngas and then into a variety of important chemicals is the most important way for the effective utilization of natural gas. The study of methane reforming with carbon dioxide has been carried out for over ten years, but its industrial application has been limited for the rapid deactivation of catalysts, however, it appears as an important alternative way to obtain syngas and has received more attention again in recent years from the viewpoint of environmental protection and industrial development. The degradation of catalysts is all along the problem for methane reforming with carbon dioxide, due to the carbon deposition on active sites and/or catalytic supports and sintering of active components at high temperatures. With base metals and modified alumina support, the present work has developed highly stable catalysts free of coke formation and sintering of active components. Firstly, copper-nickel alloy in homogeneous nanoparticles (NPs), which has never been used for the purpose in advance to supporting, is primarily synthesized and then supported as catalytic centers on alumina. It is found that the CuNi alloy catalyst with the Ni to Cu ratio of unity totally prohibits the carbon deposition on the active centers while keeping high activity for the reforming reaction. Secondly, the modification of alumina by zirconia coating before CuNi alloy supporting, drastically restrains the coke on the support, and more importantly, prevents the reaction of Cu in the alloy with alumina at high temperatures and hence promotes the stability of active alloy NPs. At the end, after supporting the CuNi alloy NPs on zirconia coated alumina, a thinner layer of zirconia is again coated onto the catalyst, with which the CuNi NPs are basically free of sintering while keeping high activity. The state-of-the-art catalyst is proved to be highly stable for methane reforming with carbon dioxide at high temperatures and high space velocity, and the deactivation constant is found close to zero in a long-term operation.2. The production of methanol from syngas with methane as the raw material is a common way in industry, and recently the study of methanol to olefin (MTO) has been promoted, with several sets of plant constructed. The acid property and pore structure of the MTO catalyst, HZSM-5, can be adjusted by changing the Si/Al ratio or through surface modification, and how to selectively produce propylene is an important direction for its higher value. An improved transient12CH3OH/13CH3OH switching method is used at steady-state conditions with a computer-controlled multi-position valve to distinguish the formation paths of propene and ethene over HZSM-5zeolites in the methanol-to-olefin process for understanding the effects of Si/Al ratios and the carbonaceous deposited in the zeolites. By carefully analyzing the isotope distribution in products in short time intervals at transient state, it is demonstrated that a fraction of the carbonaceous species is active and participates in the methanol reactions. On high silica zeolite, the active carbonaceous species are responsible for the production of ethene, while propene is formed mainly through rapid alkene methylation in zeolite channels. High Si/Al ratio of zeolite leads to high ratio of propene to ethene in products of methanol-to-olefin process.3. In order to investigate the surface polarity of heterogeneous catalyst for reactions with large difference in polarity of the reactant and product molecules, the esterification between n-butanol and acetic acid was catalyzed by SBA-15with a heteropoly acid fixed in the channels, which was synthesized with different hydrophilic/hydrophobic property. In a rigorous sealed batch reactor, the conversions of the reactants surpass the limit of chemical equilibrium with the hydrophilic catalyst, from which the hydrophobic n-butyl acetate can be rejected and the counter-reaction of hydrolysis is then suppressed.As the above mentioned results, specific traditional reactions have been studied from new viewpoints on the basis of remaining the reactivity, product selectivity and catalyst stability, and these results are practically important to develop catalysts for the relevant reactions in industry.