Study On The Nickel-based Catalysts With Bimodal Porous Structure Modified By Alkaline Promoter And Their Catalytic Performances In Dry Reforming Of Methane

There has been an increasing interest in improving the environment and applying the resources rationally.Methane and carbon dioxide as the main greenhouse gases,with the stable structure.It is an essential point to solve the problem of the greenhouse effect by transforming the two gases rationally.Dry reforming of methane could utilize methane and carbon dioxide simultaneously.The product,synthesis gas,can be used to prepare other compounds,which has a good development prospect.The development of catalysts are the key to this reaction.Nickel-based catalyst has attracted intimately attention.The advantages of nickel-based catalysts include:high activity and economy.However,it is easy to sinter and deactivate due to carbon deposition at high temperature.Aiming to solve the problem of carbon deposition,it is necessary to take measures to prevent the generation of carbon deposition and accelerate the rate of eliminating the carbon deposition.Choosing Al2O3 as the carrier and add alkaline promoters to modify the acidic sites on the surface of the catalysts to explore the stability and carbon deposition resistance of the catalysts.MgO and La2O3 were chosen as the alkaline additives for the modification of nickel-based bimodal pore catalysts.Combining the synergistic effect of bimodal porous structure and chemical effect,the effects of doping with different contents of MgO、La2O3 on the catalytic performance of nickel-based bimodal pore catalyst were explored.A series of characterization have carried out to analyse the performance of catalysts,such as N2 physical adsorption-desorption,XRD,H2-TPR,CO2-TPD,TPH,TG,Raman and so on.The specific research contents were as follows:(1)By preparing nickel-based bimodal pore catalysts with different MgO contents(0%,1%,2%,3%).It was concluded that the performance of the MgO doped catalyst has been significantly improved.The activity and stability of the catalyst doped with 2%MgO were the best.The conversion of methane and carbon dioxide of this sample was only dropped 1.35%and 1.43%with 80 h time on stream.All MgO-doped catalysts had low carbon deposition.The weight loss of the sample doped with 2%MgO was only 1.82%,and the carbon deposition was amorphous carbon,which was the easiest to be eliminated.While the weight loss of the catalyst without MgO doping was as high as 5.45%.This was related to the alkaline additives that can promote the elimination of carbon deposition.The difference performances between single pore MgO-doped catalyst and bimodal pore MgO-doped catalyst were explored.The results showed that the carbon deposition resistance performance of single pore MgO-doped catalyst was poor.This was mainly due to the macroporous structure which enhances the carbon holding capacity of the catalyst.(2)The effect of doping with different lanthanum oxide content on the performance of nickel-based bimodal pore catalyst was explored.It was concluded that a small amount of lanthanum oxide doping could improve the performance of the catalyst,and the introduction of excessive lanthanum oxide destroyed the structure of the catalyst.The catalytic performance of the nickel-based bimodal pore catalyst doped with 3%La2O3 was the best.The conversion of methane and carbon dioxide of this sample were only dropped 0.72%and 0.21%with 80 h time on stream.TPH analysis showed that when La/Al≤3%,there was only the diffraction peaks of amorphous carbon,while La/Al>3%,the diffraction peaks of layered carbon and graphitic carbon appeared,indicating that the appropriate amount of lanthanum oxide dop played an important role in eliminating carbon deposition.