| Currently, the hydrogen is mainly produced though the reformation of fossil fuels. However, great amount of COx is produced in these processes, which lead to serious environment pollution. Comparing with these processes, the direct decomposition of nature gas could produce hydrogen with high purity. However, the catalyst deactivation is still a problem.In the current investigation, we designed a type of new catalyst to resolve the catalyst deactivation problem. Certain metals were heated to a molten state to catalyze the decomposition of hydrocarbons to produce hydrogen and carbon. In a quartz reactor, a methane conversion of 23% with hydrogen selectivity of 100% was reached. A catalyst lifetime of more than 67 hours was achived, which is very difficult to obtain from regular solid state catalysts.It was found that higher temperature favors methane decomposition. However, the catalyst stability was not good and the lifetime of catalyst was shorted at relatively higher reaction temperature. The increasing of catalyst loading could enhance the decomposition of hydrocarbons, but when the amount of catalyst loading was higher than certain amount, there was no further increase in hydrocarbon conversion. At the same conditions, we investigated the decompositions of ethane and propane over molten magnesium. The results showed that even higher hydrocarbon conversions were achieved. However, carbon containing byproducts were formed, which led to the hydrogen selectivity decrease.Through the in-situ IR characterizations and catalytic reaction, it was thought that methane reacted with magnesium to form magnesium carbide intermediates and hydrogen, and then the magnesium carbide intermediates further decomposed to magnesium and carbon to complete the catalytic cycle. In the reaction, Magnesium was found evapourated from the bottom of the reactor and condensed in the up section of the reactor. The magnesium evapouration might be the reason of catalyst deactivation. However, the magnesium evapouration automatically separates catalyst from product, which makes the catalyst recovery easy.Besides the light alkanes, we found that the molten matel catalyst could also catalyze the decomposition of high molecular weight hydrocarbons, such as plastics and rubber. In an investigation of polyethene decomposition, almost 100% of hydrogen element recovery was obtained. In the decomposition of rubber,60% hydrogen recoverage was obtained. The current investigation offered altanative approach to recover hydrogen and carbon from waste hydrocarbon materials.We also examined the catalytic activities of other low melt point metals, such as sodium and zinc. However we found that sodium did not show obvious improvement comparing with magnesium at similar reaction conditions. Metal zinc was found not to be active for hydrocarbon decomposition reactions.As part of dissertation investigation, the pesticide intermediate methyl 3, 3-dimethoxypropionate was succeefually synthesized from the oxidation of acrylic acid in methanol. The reaction carried out efficiently over the Wacker catalyst PdCl2/CuCl2. Conducting reaction at 35?and 5 atm pressure for 6 h with an acrylic acid to methanol mol ratio of 1:4,95.2% of acrylic acid conversion and 90.6% of 3, 3-dimethoxypropionate selectivity were obtained over PdCl2/CuCl2. In this process, it is proved that the methanol acted as both reactant and solvent. The investigation indicated that the possible reaction mechanism of the reaction could be that acrylic acid reacted with methanol to form methyl acrylate by self-catalyzed esterfication reaction, then the methyl acrylate was oxidized to aldehyde intermediate over PdCl2/CuCl2. The aldehyde intermediate reacts with methanol to form the target product. The oxidation and aldehyde-alcohol condensation reaction moves the self-catalyzed esterfication reaction equilibrium towards the formation reaction of methyl acrylate, which finally drives the reaction to the completion. |
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