Preparation And Performance Of Promoted Multimetal Co-based/AC Catalysts For Carbon Dioxide Reforming Of Methane

Dry reforming of methane, which offers several advantages in the utilization of rich methane gas and CO₂ the reduction of greenhouse gases emission and the transmission of chemical energy, has received considerable attention in recent years. At present, the catalysts for the reaction at home and abroad studies have been largely focused on precious metals and transition metal. Precious metal catalysts is expensive, and transition metal catalysts has low stability. Activated carbon has the advantages of abundant pore structure, large specific surface area, high mechanical strength and high temperature resistance. So activated carbon is widely used as a carrier. The transition metal supported on activated carbon can improve the activity and stability of the catalyst. In this paper, multi metal catalysts were prepared by using activated carbon as the carrier, Co as active component, Ca and Cu as promoted components. The effects of impregnation methods, the types of promoter, the content of additives, the calcination temperature and the calcination time on the catalyst were studied. The catalysts were characterized by TG, SEM, BET, XRD and XPS techniques. The main research achievements are as follows:1. The optimized preparation condition of Co-CaO/AC catalysts is as follows: adopting co-impregnation method to load active constituent, an optimal calcium loading of 14 wt.%, calcined at 500℃ for 4h. The conversion of methane and carbon dioxide were maintained at about 89% and 93% respectively, no obvious deactivation is observed in the 2000 minutes.2. BET and SEM showed that adding Ca metal to Co/AC catalyst increased the specific surface area of catalyst and improved the distribution uniformity of active metal. H₂-TPR, XPS and XRD analysis showed that Ca₃Co2O₆ was generated on the catalyst by the addition of CaO, the generated Ca₃Co2O₆ can provide new active site in the reaction, at the same time, Ca metal promoted the carbon balance between CH₄ and CO₂ for CH₄ cracking generates and CO₂ eliminates the sedimentary carbon, thus maintaining catalyst activity and stability.3. The optimized preparation condition of Co-Cu-CaO/AC catalysts is as follows: using co-impregnation method to load the active component, an optimal Cu（NO₃）2?6H₂O impregnation amount of 0.002mol/L, calcined at 500℃ of 4h. Under 750℃ reaction temperature and 200 minutes reaction time, Co-Cu-CaO/AC exhibited good activity and stability, the conversions of CH₄ and CO₂ were 48% and 68% respectively and H₂/CO syngas ratio maintained dioxide were maintained at about 96.7% and 97.0% respectively within continuous operation of 1200 min at 900℃.6. The XRD indicated that Co₃O₄ and Co2MgO4, which are more reducible, were formed in preparation of Co-MgO/AC catalysts calcined at 400℃. When the calcination temperature is too high, it will be difficult to reduce the formation of（Co,Mg）O. BET showed that a proper amount of MgO promoter could increase the catalyst’s surface area as the cooperative effect with activated carbon.7. The optimum process conditions for Co-Cu-CaO/AC catalytic reforming of CH₄/CO₂ were optimized: reaction at 800℃, CH₄/CO₂ ratio is 1,the raw gas is 120mL/min. Based on the proposed reaction mechanism of DRM reaction on the Co-Cu-CaO/AC catalyst, CH₄ molecules adsorbed to the Co particles formed free hydrogen and surface carbon species C-Co; CO₂ molecules adsorbed onto CaO to form bidentate carbonate species CaCO₃; C-Co and bidentate carbonate species CaCO₃ reaction produces carbon monoxide.