Study On Highly Efficient Catalysts For Methane Decomposition

With the depletion of coal and oil,the proportion of natural gas in the energy structure is increasing,so the transformation of CH4 has strategic significance.Environmental pollution and climate change caused by greenhouse gases are becoming more serious,forcing us to develop cleaner,more efficient,safe and sustainable energy.Hydrogen is regarded as the most potential energy carrier in the 21st century.Catalytic methane decomposition,which converts methane to clean hydrogen and solid nanocarbon,is considered as a potential way to produce hydrogen.Highly efficient catalysts will accumulate large amounts of carbon during the reaction,which may cause catalyst deactivation.Therefore,it is necessary to study the structure-activity relationship of the catalysts for methane decomposition and the carbon produced in the reaction.In this thesis,novel SiC material and conventional SiO2 were used as catalyst support.CDC-SiC(CDC,carbide derived carbon),was fabricated by halogen extraction method with commercial low specific surface area SiC as raw material.This material was coverd with high specific surface area carbon layer.The catalysts were characterized by X-ray diffraction(XRD),N2-sorption,thermogravimetric/differential scanning calorimetry(TG/DSC),transmission electron microscopy(TEM),temperature-programmed reduction(H2-TPR).The methane catalytic decomposition reaction was carried out at 700 °C under atmospheric pressure.The feed gases consisted of CH4 and Ar with a volume ratio of 1:1,and the gas hourly space velocity(GHSV)was 48000 ml·h-1·g-1cat.The catalytic performance of the catalysts was represented by the carbon yield within 60 min.The main conclusions are listed below:1.The weight gain on Ni/CDC-SiC is 0.35 gC-g ’cat,which is the highest in Ni/AC,Ni/SiC and Ni/CDC-SiC.Ni/AC showed almost no activity.2.In Ni/CeO2-CDC-SiC catalysts with different CeO2 content,the highest carbon yield reached 1.44 gC g-1cat cat when CeO2 was 30 wt%.The specific surface area and the pore volume of Ni/CeO2-CDC-SiC increased.The better dispersibility and reduced size of Ni particle contributed to the better activity.3.In the series Ni-Fe/SiO2 catalysts,the highest carbon yield,1.75 gC-g-1cat was obtained with the optimum Fe content of 1 wt%.Large amounts of carbon nanotubes were observed on the spent catalysts.The improved catalytic performance may owe to the reduced Ni particle size caused by the doping of Fe.