چكيده به لاتين
Methane dry reforming with CO2 attract much attention by converting two greenhouse gases to syngas with H2/CO ratio close to 1. The catalyst sintering and deactivation due to carbon deposition are the major drawback of DRM reaction. There are many solution to remove carbon such as use of proper support and promoters. In this thesis, Zinc aluminate spinel with specific features as the high thermal stability, high mechanical resistance and low surface acidity, was used as the support of Nickle catalyst and evaluated in methane dry reforming for the first time. ZnAl2O4 with nano-crystalline structure was synthesized by co-precipitation method and further impregnated by different amounts of Ni. Catalyst with 12.5%wt Ni, showed the highest initial conversion (69.8%) in DRM at 700˚C temperature, GHSV=18000 ml/(h.gcat), CO2:CH4:N2=1:1:1 , but after 8 hours of reaction the conversion was reduced due to a large amount of coke deposition (according to TG analysis). In order to control carbon deposition and increase catalyst stability, Ce promoter was used with 3,5 and 7% wt loading. The conversion was increased with addition Ce due to the modification of the nickle dispersion and active phase-support interaction. High oxygen mobility of Ce enhanced coke gasification and reduced the carbon deposition and therefore improved catalyst stability. Catalyst performance was significantly affected by the amount of cerium. Although catalyst with 7%wt Ce showed the higher initial conversion (75%), but catalyst with 5%wt Ce was more stable (loss activity=3.6%) and it was selected as the optimal catalyst. After that, the effect of temperature at 650-800˚C range was investigated on the conversion of Ni(12.5)/ZnAl2O4 and Ni(12.5)/Ce(5)-ZnAl2O4 catalyst. The conversion of both catalysts was increased with increasing reaction temperature and Ce modified catalyst exhibited higher conversion rather than un-doped catalyst in all temperature examined. The highest conversion (82%) was achieved over the sample with 5 wt.% of cerium at 800 ˚C .
