Load Type Ni Base The Development Of Methane Catalytic Cracking Catalyst

Lots of deuteraled and tritiated methane has been generated as a result of the interaction between the plasma and the first wall during the D-T fusion reaction in ITER (International Thermonuclear Experimental Reactor). Therefore, it’s very important to recover deuterium and tritium from the deuterated and tritiated methane by means of methane decomposition. In this thesis which was based on the literature review, methane catalytic decomposition over four kinds of solid catalysts such as Ni-SiO2, Ni-La2O3-SiO2, Ni-Cu-SiO2and Ni-Fe-SiO2prepared by different methods (impregnation method, co-impregnation method and sol-gel method) was investigated.The investigation on methane decomposition over these catalysts not only solved the problems on the catalyst preparation, methane catalytic decomposition and the regeneration of the deactivated catalysts but also established the catalyst preparation techonology and the research method of the catalytic performance of methane decomposition and accumulated the experience for decomposing the deuterated and tritiated methane to recover deuterium and tritium. The results obtained from the research were displayed as follows:(1) The Ni-SiO2catalysts doped with La2O3(Ni-La2O3-SiO2) have been prepared by co-impregnation method. The Ni-SiO2catalysts with La/Ni=0.3showed the best catalytic activity and the longest lifetime during methane decomposition at550℃among these catalysts. The changing tendency of Ni particle size during methane decomposition was different for Ni-La2O3-SiO2with different La/Ni (molar ratio). The Ni particle size of Ni-SiO2(La/Ni=0) decreased continuously during methane decomposition, however, the Ni particle size of Ni-SiO2(La/Ni=0.3) increased continuously during methane decomposition. The structure of carbon filaments generated during methane decomposition depended on La/Ni:the carbon filaments generated over Ni-SiO2with La/Ni=0.3was longer and thicker than those generated over other catalysts.(2) The Ni-SiO2catalysts doped with Cu and Fe (Ni-Cu-SiO2and Ni-Fe-SiO2) have been prepared by sol-gel method and the influences of the Cu and Fe contents in Ni-SiO2as well as the reaction temperature on methane decomposition have been investigated. The Cu and Fe species in the fresh Ni-Cu-SiO2and Ni-Fe-SiO2catalysts mainly existed in the form of CuO and NiFe2O4, respectively. Further SEM-EDX and XRD studies suggested that the introduced Cu and Fe entered into Ni lattice and Ni-Cu alloy and Ni-Fe alloy were formed in Ni-Cu-SiO2and Ni-Fe-SiO2catalysts reduced by hydrogen, respectively. The introduction of10%Cu and10%Fe (mass fraction) extended the lifetime of Ni-SiO2catalyst during methane decomposition at650℃, however, when more Cu and Fe was introduced, the methane conversion decreased. The structure of carbon filaments generated over Ni-SiO2, Ni-Cu-SiO2and Ni-Fe-SiO2was quite different. The results of TEM studies proved that "multi-walled" carbon filaments formed over Ni-SiO2catalyst, while "bifurcated" and "bamboo-shaped" carbon filaments were generated over Ni-Cu-SiO2and Ni-Fe-SiO2catalysts at650℃, respectively.(3) The activity and lifetime of deactivated Ni-SiO2, Ni-Cu-SiO2and Ni-Fe-SiO2catalysts after regeneration with air was also investigated. The activity of Ni-SiO2catalysts decreased as the regeneration times increased, while the lifetime didn’t change apparentely. The lifetime and catalytic activity of Ni-Cu-SiO2both decreased after regeneration with air which was different from that of Ni-SiO2and the lifetime during methane decomposition after regeneration with air increased with the increase of the Cu content. The catalytic performance of deactivated Ni-Fe-SiO2after regeneration with air was completely different from that of Ni-SiO2and Ni-Cu-SiO2. The activity of Ni-Fe-SiO2after regeneration with air increased, while the lifespan of Ni-Fe-SiO2decreased. Additionally, spherical carbon structure was observed after methane decomposition over Ni-SiO2, Ni-Cu-SiO2and Ni-Fe-SiO2catalysts during the second and the third regeneration cycle which might be the reason why the catalytic activity and lifetime of the three kinds of catalysts were influenced after regeneration with air.(4) The overall catalytic performance of Ni-SiO2. Ni-La2O3-SiO2, Ni-Cu-SiO2and Ni-Fe-SiO2has been compared with each other. The activity and stability of75%Ni-25%SiO2was higher than those of Ni-La2O3-SiO2with La/Ni=0.3. Ni-Cu-SiO2catalysts exhibited the best catalytic performance among the five kinds of catalysts for they showed a longer lifespan and a better stability than75%Ni-25%SiO2and Ni-Fe-SiO2at650℃. At the same time, Ni-Cu-SiO2catalysts also showed the best performance during the methane catalytic decomposition and regeneration with air cycles for the lifetime and the activity of Ni-Cu-SiO2during the three cycles were better than all the other catalysts...