Study On Co Based Activated Carbon Catalyst Of CH₄-CO₂ Reforming For Synthesis Gas

Carbon dioxide reforming of methane can make use of methane and carbon dioxide of greenhouse gases,Which can can make them into an ideal raw material for methanol,liquid fuels,and so on.It provides an effective way to reduce emissions of carbon dioxide and the utilization of methane gas.The thermodynamic properties of methane and carbon dioxide are very stable.In order to reduce their activation energy,the development of reforming catalyst is particularly important.At present,there are two kinds of catalysts,such as noble metal catalyst and transition metal catalyst.The noble metal catalyst has high activity,but the precious metal resources with a expensive price are limited,which is not conducive to industrial use.Transition metal catalysts are susceptible to carbon deposition,sintering,poisoning and structural changes.Therefore,it is the core content of CO₂ reforming CH₄ to select a cheap catalyst with good activity and stability.Compared to metal catalysts,carbon-based catalysts have a sufficient source and a significant price advantage.The coke produced in the reaction can also act as a carrier and an active site.Activated carbon is widely used as catalyst or catalyst carrier because of its rich pore structure,large specific surface area,good adsorption performance,stable chemical properties and easy regeneration.In this paper,the effects of different supports on the performance of the catalyst are investigated.It is found that the carrier has a significant effect on the performance of the catalyst.When activated carbon and modified activated carbon are used as a carrier,its catalytic activity is significantly higher than carbon molecular sieve of a carrier,which is mainly due to the specific surface area of activated carbon and modified activated carbon than the surface area of carbon molecular sieve.It is also found that the specific surface area of modified activated carbon was reduced,but the reactivity did not decrease.It is found that the specific surface area and pore size have an effect on the activity of the catalyst,but not the only factor affecting the activity of the catalyst.SEM shows that the dispersion of the active components on the different carriers was significantly different.The dispersion of the active components on the modified activated carbon is the best,the modified activated carbon is the second,and the carbon molecular sieve is the worst.At the same time,it is found that the interaction between the metal and the carrier was also different when the carrier is different.The order of the strength is carbon molecular sieve> activated carbon> modified activated carbon.The overall performance of the carrier determines the performance of the catalyst.On the basis of the study of the carrier,the influence of the cerium and tungsten on the activity of the catalyst prepared by different activated carbon is also investigated.Through the orthogonal experiment to determine cobalt,cerium,tungsten three components significant sequence of catalysts in different preparation of activated carbon in the catalyst.The order of the three components of cobalt,cerium and tungsten is the order of cobalt> tungsten > Cerium in Xinhua activated carbon.In the modified activated carbon and Datong activated carbon prepared catalyst,the most obvious significance cobalt has the most obvious significance,while cerium and tungsten have the same significance.According to the order of the three components of cobalt,cerium and tungsten in different activated carbon,the best dipping concentration of cobalt,cerium and tungsten on the different carriers is determined in turn,and the optimum concentration of the three components was determined.The optimal concentration of cobalt nitrate impregnated by Xinhua activated carbon is 33.33g/100 g H₂O,the concentration of cerium nitrate is 2.52g/100 g H₂O,the concentration of ammonium metatungstate is 3.36 g/100 g H₂O.The optimal concentration of cobalt nitrate impregnated by modified activated carbon is 33.33 g/100 g H₂ O,the concentration of cerium nitrate is 1.68 g/100 g H₂O,the concentration of metatungstic acid ammonium is 1.26g/100 g H₂O.The optimum concentration of cobalt nitrate impregnated by Datong activated carbon which is modified by Potassium Permanganate is 38.88g/100 g H₂O,the concentration of cerium nitrate is 1.68 g/100 g H₂O,the concentration of ammonium metawolframate 1.26g/100 g H₂O.The results of XRD show that the calcination temperature and calcination time have a significant effect on the crystal size of the catalyst.The catalyst with the best calcination temperature and calcination time has the highest activity,which has the smallest crystal size.The optimum calcination temperature of the activated carbon catalyst is 600 ?,the calcination time is 2h,the average particle size of the catalyst is 28.8nm;The optimum calcination temperature of the modified activated carbon catalyst is 500 ?,the calcination time is 4h,the average particle size of the catalyst is 29.4nm;The optimum calcination temperature of Datong activated carbon modified by potassium permanganate is 600 ? and the calcination time is 3 h,the average particle size of the catalyst is 27.9 nm.The results of XRD and SEM show that the addition of cerium and tungsten can significantly improve the dispersion of the catalyst and reduce the crystal size of the catalyst.The characterization of BET showed that the specific surface area and pore volume of the catalyst is increased more than the catalyst without adding additives.The results showed that the addition of promoter could promote the adsorption of each component.With the increase of the adsorption amount,the dispersion increases and the crystal size decreases,?It can provide more active sites for the same amount of catalyst and improve the catalytic activity of the catalyst.H₂-TPR showed that the addition of cerium and tungsten has different influence on metal-carrier interaction force.The addition of promoter on Xinhua activated carbon weakens the metal-carrier force of the catalyst,while in the modified activated carbon and Datong activated carbon, the addition of promoter enhances the metal-carrier force of the catalyst.XPS shows that the relative content of Co3+ decreases and the relative content of Co2+ increases with the addition of auxiliary agent cerium and tungsten.It indicate that electron transfer occurs during the preparation of the additive,which forms a more stable chemical state and changes the chemistry of the catalyst surroundings.The cerium has a strong ability of oxygen migration,which can enhance the ability of the catalyst to reduce carbonization.It can reduce the formation of carbon deposition.Tungsten has a high melting point,which can inhibit the formation of large particles of grain and enhance the ability of the catalyst to reduce carbon.The formation of stable chemical states and the reduction of carbon deposition are favorable to the improvement of catalyst stability.