Studies On Supported Nickel Catalysts For Reforming Of Methane With Carbon Dioxide In The Presence Of O₂ Using Fluidized Bed Reactor

Converting methane and light hydrocarbons to syngas is one of the most promising utilization approaches. Reforming of CH₄ with CO₂ and O₂ to produce synthesis gas is a green process. This reaction has not only important environmental implications and utilization of natural gas. Furthermore, it can provide energy for partial autothermal reforming form CH₄ combustion. Reforming of CH₄ with CO₂ and O₂ using a fluidized bed reactor, can resolve the hot spot in reactor and sintering of active species in a fixed bed reactor. Simultaneously, the carbon deposition in CH₄-CO₂ reforming can be efficiently supressed because of oxygen input. H₂/CO in product can be modified according to the need of the post process by varying the composition of feed gas. At present, one of the key problems for the application of this process is the development of practical catalysts with good activity and stability. In this paper, commercial wearable SiO₂ was used as the support, nickel as the active component, the major work is focused on the study of Ni-based catalysts and the reaction process for reforming of methane and with CO₂ and O₂ using a fluidized bed reactor.The Ni/SiO₂ catalyst was modified by alkaline earth metal oxide in order to improve the thermal stability and the carbon deposition resistance for reforming of methane with CO₂ and O₂ using a fluidized bed reactor, it was possible to convert methane into syngas with low H₂/CO ratio (12/CO<2) at above 85% methane conversion without catalyst deactivation in 20 hours, in a most energy efficient and safe manner. Samples of the catalysts were investigated using H₂-TPR, CO₂-TPD, XRD and TEM techniques. The characterizaion results indicated that the addition of CaO, BaO and SrO was responsible for its high activity and resistance to sintering because it can produce a highly dispersed active surface area as bound-state Ni species when the catalyst is prepared at high calcined temperatures. The nickel particles tend to be highly dispersed and can be fixed by being segregated in modified support, which had a significant effect on its reduction behavior and show goodresistance to nickel particles aggregation. Reforming of methane with CO2 and oxygen was used to produce low H2/CO ratio syngas over Ni/MgO-SiC>2 catalyst under certain reaction conditions. The effect of catalyst fluidization on the conversion of methane was investigated over Ni/MgO-SiO2 and Pt-Ni/MgO-SiO2 catalysts. It was founded that the NiO-MgO solid solution was formed on the SiCh surface. When reduced with pure Hydrogen, a small quantity of nickel separated out of the NiO-MgO solid solution and stabilized by MgO. From the heating-cooling experiment and CH4/CQ2-TPSR-MS results, the Ni(Pt/Pd)/MgO-SiC>2 catalyst had good activity at relative lower temperature because of hydrogen spillover. Thus, the valence state changing can be practiced in the fluidized bed reactor, and the catalytic performance can be promoted.CeCVZrCb was used to modify SiC>2 support. Ni/(Ce)ZrC>2-SiO2 showed good activity and stability for reforming of CH4 with CO2 and O2 in a fluidized bed reactor. Results of heating and cooling profiles on un-reduced catalysts and H2-TPR showed that the reducibility of Ni/SiO2 was promoted by adding ZrO2. Catalysts with moderate reducibility had better activity in reforming of methane with CO2 and O2, eapecially in a fluidized bed reactor. Form the results of CKj-pulse-MS and CH4/CO2-TPSR-MS, It was proved that the fine structures and the dispersion were changed after adding CeC>2-ZrO2 to Ni/SiCh; the electron density of NiO increased, and the species that could be reduced at low temperature were formed on the catalyst surface, thus, the resistance to carbon deposition was enhanced. Metastable structure was formed on catalyst surface between Ni species and ZrCVCeCh because of electron transfer. It was favor to dissociative adsorption of CO2 and formed carbonyl species on the interface between Ni and ZrC>2. Thus, the activity of CO2 reforming and removing carbon deposition with CO2 was promoted.Major research was focused on the fluidized characterizations and the process of autothermal reforming of methane with CO2 and O2 using a fluidized bed reactor. Comparative study of activity, stability, TGA and Raman results between the fixed and the fluidized bed reactor was practiced, it was verified that the fluidized bedreactor was an efficient reactor for reforming of methane with CO2 and O2. The catalyst is in a permanent circulation between the oxygen-rich and oxygen-free zones. Thus, the catalyst oxidized by oxygen in the front region can transfer to the rear part where it is re-reduced and exhibits reforming activity. The high conversions and autothermal operation suggested that fluidized bed offer viable energy-efficient alterative reactor for synthesis gas generation by the reforming of methane with CO2 and oxygen, and this reaction probably complete through one-step mechanism.Primary study on reforming of methane and propane with CO2 and O2 to produce syngas was practiced in a fluidized bed reactor. The results of investigating catalysts showed that the catalysts contained Pt, Pd and Ru has good dissociative activity to light hydrocarbon. Perfect conversion of light hydrocarbon was obtained while there was serious coke on the spent catalyst. Good catalytic activity and resistance to carbon reposition were founded on Ni/SiO2 modified by CaO. Results CO2(O2>-TPSR-MS of showed that O2 input in feed gas could not only provide energy by combustion for reforming, but also redound to remove the coke which could not be eliminated with CO2. CHX or metal carbide derived from propane may promote the CH4 activation, and further research was practiced.