The Study Of Ni-based Catalysts With Composite Support For CO Methanation

Coal and natural gas is an effective way to produce alternatives to petroleumproducts. Methanation reaction has a large amount of heat release and the main problemof Ni/Al2O3catalysts commonly used in industrial applications is hard to reduce and poorthermal stability. Studies have shown that doped with rare-earth composite carrier canimprove the interaction between Ni and Al2O3, increase the catalyst performance ofresistance to carbon deposition and prevent active component aggregated and sintered. Inthis paper, because of CeO2-rich surface defects, we systematic study the interactions,surface performance, acid-base property and crystal structure between Al2O3and CeO2onthe CeO2-Al2O3composite carrier to optimize the synthesis conditions of CeO2-Al2O3composite support. Also, we investigated the adjustment and control of structure and itsrelation between CO and methanation performance.An impregnation method had been applied to prepare composite carrier to increasecerium oxide content. It also helps to reduce the reduction temperature of nickel oxideand increase the reduction amount. The composite carrier of CeO2-Al2O3couldeffectively prevent the formation of nickel-aluminum spinel. Specially,20%N40%CAJcatalyst presented higher catalytic activity, the conversion rate of carbon monoxidereached a maximum of99%at350℃, exhibit a low active temperature.The optimum condition of preparing cerium-aluminum composite carrier usingprecipitation method as follows: aging temperature was80℃, pH=10, calcinationtemperature was650℃and the ratio of cerium-aluminum was20%. Wherein the highpH can increase the solubility of Al (OH)3, as a result, the acting force between Ni and Albecame relatively reduced, and the reduction of the amount of nickel in the lowtemperature or Medium temperature of nickel catalyst significantly increased. Thenickel-aluminum spinel components generated because of the increase of calcinationtemperature inhibited the activity of the catalyst. When the reaction temperature was400℃and the catalyst was20%N20%CAC10, the conversion rate of carbon monoxidereached100%, yield and selectivity of methane get to97%and96.5%, respectively. Thecatalyst stability experiments confirmed that when the reaction temperature was450℃, the conversion rate of carbon monoxide remains above99%, yield and selectivity ofmethane get to around96%and95%respectively after50hours.A Sol-gel method had been applied to obtain cerium-aluminum composite carrierthat has a bee-hole structure. The results showed that the conversion rate of carbonmonoxide reached100%, yield and selectivity of methane get to96.3%and96%,respectively when the reaction temperature was500℃and the catalyst was20%N40%CAR750. The bee-hole structure was good for improving the catalytic activity but it alsoreduced the high-heat activity of the catalyst.A Coprecipitation method had been applied to obtain mesoporous YAlO that has acertain orderliness of worm-like pore structure and pore walls contain Al5Y3O12grains.Grain by the mesoporous connected to each other with a size of about6nm. The stabilityexperiments in50h of mesoporous catalyst NYA50h confirmed that the activity decreasedwith increasing time, heat stability of the catalyst was significantly lower than20%N20%CAC10catalyst.The catalytically active of compound carrier was higher than the same amount ofnickel aluminum catalyst loading, relatively neat hole structure could improve thecatalytic activity, bee hole was larger than mesoporous aperture, so it made the activecomponent dispersed better, shown more active component, and lower living temperature,but the hole wall was too thin to the thermal stability, with the temperature increaesed,activity droped rapidly.