Synthsis Of Novel Ni-Based Catalysts With Controned Shape For CO₂ Reforming Of Methane

CO2 reforming of methane reaction is one of the important technologies to produce synthesis gas (syngas, H2/CO) for fuel and to eliminate the greenhouse gases. There are two kinds of catalysts used in this technology, noble metal and transition metal catalysts. Nickel (Ni) based-catalysts are regareded as the most promising candidates due to their high activity and relatively low cost. But the Ni based catalysts susceptable to deactivation by metal sintering or carbon deposition. Therefore, it is of urgency to develop Ni based catalysts with improved catalytic performances.In recent years, people have realized the controllable synthesis of nano-structured catalysts with various morphologies. This can not improve the catalytic activity and/or stability of the catalyst. The controllable synthesis of nano-structured catalyst morphology provides idea for the design and development of an efficient catalyst for CO2 reforming of methane reaction. Therefore, this thesis starts with synthesis of morphology controllable ?-Al2O3. Through the electrospinning and hydrothermal synthesis techniques ?-Al2O3 nanofibre, nanoplate and nanosheet were successfully synthesized and employed as supports for Ni based catalysts. According to its own characteristics, the catalytic performance of these three kinds of catalysts in CO2 reforming of methane reaction was systematically investigated. The main results are summaried as follows:(1) In the electrospinning synthesized Ni/?-Al2O3 catalyst, metallic Ni nanoparticles were highly dispersed on ?-Al2O3 nanofibres with an average particle size of 3.4 nm. Compared with the Ni/?-Al2O3 catalyst conventionally prepared via incipient impregnation method using commercial ?-Al2O3 powder as the support, the electrospun Ni/?-Al2O3 catalyst exhibits improved metal dispersion, leading to higher activity and superior coke resistance in CO2 reforming of methane.(2) Ni/?-Al2O3 nanoplate catalyst exhibited high initial activity. Its initial activity was about 15% higher than that of the conventional catalyst. But the stability of the Ni/?-Al2O3 nanoplate catalyst was relatively poor. The activity of the catalyst decreased markedly after reaction of one hour. HR-TEM images demonstrate sintering occurred for metallic Ni nanoparticles during reactions. In addition, the carbon deposition on the Ni/?-Al2O3 nanoplate catalyst was severe. H2-TPR characterizations confirmed that metal-support interaction on the the Ni/?-Al2O3 nanoplate catalyst was weaker than that on the conventional catalyst, which may explain the observed relatively poorer stability property.(3) The metal-support interaction was strengthened by adding 6 wt% CeO2. The catalytic activity and stability of the catalyst was improved simultaneously. The conversion of methane and carbon dioxide reached 66% and 78%, respectively, and the catalytic activity remained stable after 6 h. After adding CeO2 in the Ni/?-Al2O3 nanoplate catalyst, coke deposition on the catalyst decreased significantly. That is, anti-coking property of the catalyst was significantly improved.(4) Compared to Ni/?-Al2O3 nanoplate catalyst, Ni/?-Al2O3 nanosheet catalyst had larger specific surface area, higher metal Ni dispersion and superior catalytic stability. In adittion, the Ni/?-Al2O3 nanosheet catalyst only has a small amount of carbon after reaction of 6 h, suggesting excellent resistance to carbon deposition.