Superhydrophobic Catalyst Coating For Hydrogen Mitigation And Superhydrophobic Ceramic Membrane Contactor

Shortage of energy sources and environment pollution in in the world are becoming more serious.For the development and utilization of energy,there are requirements for hydrogen mitigation,for example,in the case of the hydrogen generation during a severe accident for a nuclear power plant and the hydrogen off-gas of hydrogen fuel cells.For converting hydrogen into water,supported noble catalysts have been reported to be the most effective.Those catalysts,however,have to face the challenges of impurities in the practical applications,which may lead to an obvious decrease in catalytic activity.Given the flammable and explosive properties of hydrogen,the deactivation might result in a big threat to safety.To address these issues,further investigations should be conducted to improve the catalytic activity and stability to better meet the requirements in the real applications.However,few reports can be found on these issues.In this thesis,the catalysts were modified from hydrophilicity to superhydrophobicity to remove the hydrogen off-gas for PEFCs and to get rid of the generated hydrogen during a serious nuclear accident.Besides,the superhydrophobic modification was applied to ceramic membranes,which were used for NO removal.The main reseaech contents and findings are as follows:?1?Superhydrophobic Pt-Al₂O₃ catalyst coating concerning oxidation of hydrogen off-gas from fuel cellTo ignite the hydrogen oxidation at room temperature with negligible induction period,the Pt-Al₂O₃ catalyst coatings on the walls were modified from hydrophilicity to superhydrophobicity.The suitable hydrophobic modification significantly promoted catalytic activities and stabilities of the catalyst coatings under both humid and dry feed stream conditions.The results of DPD simulation showed that the higher grafting density provided stronger repulsive force on water?favorable effect?and meanwhile more barriers for accessibility of the reactants to the active metal species?unfavorable effect?.Under the humid feed stream condition,the catalytic activities heavily depended on the hydrophobicity extent with the most active catalyst of 5WM-Pt-Al₂O₃ showing the biggest contact angle of 150°.The hydrogen concentrations at the outlets of CPR?channel plate reactor?5WM-Pt-Al₂O₃ slightly increased from from 450 ppm?at 5 min?to 632 ppm?at 130 min?.No hydrogen was detected at the microchannel reactor?coated with 5WM-Pt-Al₂O₃?outlet at 333 K.The microchannel reactor with superhydrophobic catalyst coatings showed great potential for conversion of hydrogen off-gas of PEFCs to water.?2?Superhydrophobic Pt-Pd/Al₂O₃ catalyst coating for hydrogen mitigation system of nuclear power plantSuperhydrophobic Pt-Pd/Al₂O₃ catalyst coatings were prepared for PAR system by wet impregnation method and the grafting of FAS.The formation of a Pt-Pd intermetallic compound was confirmed by in situ diffuse reflectance infrared Fourier transform infrared spectroscopy for the Pt-Pd/Al₂O₃ catalyst.The Pt-Pd/Al₂O₃ catalyst exhibited a superior resistance of water poisoning to the monometallic catalysts.In addition,compared with the monometallic catalysts,the least influence by the iodine poisoning was observed for the Pt-Pd/Al₂O₃ catalyst,which is attributed to the smallest influence on the bindings of H2 and O₂ on the Pt-Pd intermetallic compound by the iodine addition?carried out by density functional theory calculations?.Within the initial 60 min,in the case of 20 ppm iodine poisoning,hydrogen conversion for Pt0.5Pd0.5 declined from 90.1%?at 10 min?to 32.8%?at 60 min?,which was still much higher than that of the monometallic catalysts.?3?Pd@CeO₂/Al₂O₃ catalyst coating for hydrogen mitigation system of nuclear power plantPd@CeO₂ core-shell nanostructured catalysts were prepared to alleviate the aggregation under high temperature by a biomolecule-assisted method.The core-shell structure was assembled with a Pd particle size of 9^-13 nm in the center and surrounded by a shell of CeO₂ in 10-20 nm thickness.For the hydrogen mitigation,the Pd@CeO₂/Al₂O₃ catalyst exhibited a strong resistance to iodine poison with the hydrogen conversion of 32.8%?120 min?,which is much higher than those of Pdi.o and Pt0.5Pd0.5.This is attributed to the exsitance of small nanopores in the CeO₂ shell?1.52 nm?,which creates a strong barrier for the diffusion of iodine from the outsides to the active sites located in the core of the Pd@CeO₂.?4?Fabrication of a superhydrophobic ceramic membrane contactor and the application in the NO removalWe proposed a new denitration method by using superhydrophobic ceramic membrane contactor.After grafting by FAS,the ceramic membrane achieved a contact angle of 153° and with a trans-membrane pressure of 6 bar.The NO gas from a simulative flue gas was oxidized by H2O₂ aqueous solution using the superhydrophobic membrane.The high-pressure gas entered the membrane module from the shell side and absorbent solution was pumped into the lumen side.To minimize the detrimental effects of low solubility of NO in water,the gas pressure was enhanced to 6 bar.With the optimized parameter,the NO removal efficiency?27.1%?and mass transfer rate(15.8 mol m2 h^-1)both increased with an increase in gas pressure from 0 to 6 bar,respectively.The experimental results showed great potential for removel of gas with low solubility.