Carbon Dioxide Reforming Of Methane Over Ni-based Catalysts

CH₄-CO₂ reforming for syngas production is a promising way for effective use of CO₂, which has great significance for comprehensive utilization of resources and environmental protection. At present, looking for the highly efficient and stable catalysts for carbon dioxide reforming reaction of methane is the key to the technology.This thesis mainly used doping metal additives and improving the catalyst preparation method, explore their modulations on the performance of the catalysts used in carbon dioxide reforming of methane. The characteristics of the multi metal catalysts for methane carbon dioxide reforming were studied in detail. The study mainly designed two kinds of catalysts（Ni-Cu-Mo/Al2O3 and Ni-Ce/TiO₂-Al2O3）, and also carried out the activity evaluation of these two kinds of catalysts to determine the better reaction conditions. At the same time, the characteristics of the catalysts were checked with X-ray diffraction（XRD）, Brunauer-Emmett-Teller（BET） analysis, scanning electron microscope（SEM）, X-ray Photoelectron Spectroscopy（XPS）, Thermogravimetric analysis（TG）, Energy Dispersive Spectroscopy（EDS） and temperature-programmed desorption of CO₂（CO₂-TPD）.The catalytic activity of Ni based catalysts with doping metal additives was significantly better than the single metal catalyst Ni/Al2O3. The alloy structure and metal oxide formed between activated components and metal additives could promote the CH₄/CO₂ reforming. The Ni-Cu-Mo/Al2O3 catalyst prepared by doping Cu and Mo metal additives showed the best catalytic activity among the catalysts prepared traditional impregnation method. The chemical composition of the Ni-Cu and Ni-Mo alloys were found to have a higher dispersed state in the Ni-Cu-Mo/Al2O3 catalyst. The Ni-Cu-Mo/Al2O3 catalyst with Ni/Mo mass ratio of 0.75 was better than other Ni-Cu-Mo/Al2O3 catalysts. The Ni-Cu-Mo/Al2O3 catalyst with Ni/Mo mass ratio of 0.75 had higher BET surface area, more alkaline activity sites and uniform distribution, which showed potential for carbon dioxide reforming of methane. Results indicated that, the catalysts with Ni/Mo mass ratio of 0.75 exhibited better activity at the optimum temperature of 800℃. At the reaction conditions of 800℃ and a space velocity of 182 mL·g-1·min-1, the conversion rates of CH₄ and CO₂ were 97.7% and 99.1%, respectively, the selectivity of CO and H2 were 94.4% and 92.1%, respectively. The characteristic of the catalyst with Ni/Mo mass ratio of 0.75 was highly active and the conversion of CH₄ and CO₂ were still over 90% after 60 h.This study adopted the modified impregnation method and the improved sol-gel method to make a series of fixed mass ratio of the supported Ni-Ce/TiO₂-Al2O3 catalyst with the introduction of plasma modified the catalysts. SP-RP catalyst prepared by improved sol-gel method and IP-RP catalyst prepared by modified impregnation method showed higher catalytic activitives. The activity evaluation and characterization analyses showed that the plasma-assisted method had a significant effect on catalytic performance. The conversions of methane and carbon dioxide on Ni-Ce/TiO₂-Al2O3（SP-RP） catalyst could reach 52.29% and 48.33% at 600℃ and 96.81% and 97.87% at 800℃.The introduction of plasma of the SP-RP and IP-RP catalysts showed smaller particles, improved the metal dispersion, and provided larger specific surface area, as well as more alkaline active sites, which was responsible for good catalytic performance. The strong alloys of Ni₃ Ti formed in the SP-RP and IP-RP catalysts could improve the antioxidant capacity of Ni significantly, which could improve the catalytic activity of the catalyst and prevent the accumulation of carbon.