Study On Preparation,characterization And Performance Of Catalyst For CO/CO₂ Methanation

The energy distribution in China is characterized by"rich in coal,poor in oil and natural gas".Moreover,coal will continue to be the major energy source for its economy in the foreseeable future.Natural gas has emerged as one of the most promising sources in China due to its clean and high efficiency.However,the gap between domestic natural gas supply and demand is further worsened with its faster consumption relative to the slowing production,increasing the risk of dependence on foreign natural gas.In this situation,synthetic natural gas?SNG?from coal in China should be vigorously developed,which is considered to be a clean and effective way of energy utilization.The key technique is the methanation process,therefore,developing highly efficient methanation catalysts and process technology are considered as promising applications with high academic value.Ni-based catalysts were investigated with coal syngas as the raw material for CO methanation by comparing the common Al₂O₃ support and different preparation methods?ethylene glycol?EG??modified method,direct synthesis and post synthesis methods).It can be seen that 3D-mesoporous KIT-6 as a support exhibited better catalytic performance with CO conversion of almost 100%and CH₄ yield of 75%at450^oC.Ni/KIT-6?EG?prepared by EG modified method had better catalytic activity and high temperature stability due to the formation of the smaller Ni nanoparticles with high dispersion.10Ni/KIT-6 modified by adding?V,Ce,La,Mn?additives showed better catalytic performance,and 10Ni-2V/KIT-6 exhibited the best catalytic performance with 100%CO conversion and 85%CH₄ yield at 350^oC while showed excellent catalytic stability during 60h stability test.DFT calculations were performed for the Ni₁₀V₂?111?surface to compare CO adsorption energy on the Ni?111?surface.DFT results revealed that the Ni₁₀V₂?111?surface offered two types of binding sites,which would allow a quicker regeneration of the surface sites and faster catalytic turnover,leading to the improved catalytic performance.The effects of V and Ni content on the catalytic performance for CO methanantion were investigated for xNi-yV/KIT-6.20Ni-2V/KIT-6 with 2wt%V and20wt%Ni showed the best catalytic performance for CO methanation,corresponding to CO conversion of 100%and CH₄ yield of 85%at a low temperature of 300^oC.The characterization results showed that the proper amounts of V and Ni could maintain the effective 3D mesoporous confinement effect,promote the formation of more highly-dispersed,small-grain Ni nanoparticles,and provide more Ni active sites while the appropriate V species can facilitate the dissociation of CO.These combined effects improve the catalytic activity and stability.The effects of reaction temperature,reduction temperature,space velocity and H₂/CO ratio on the catalytic performance were also investigated for CO methanation.CO₂ as methanation feedstock,not only achieves the utilization of CO₂,but also further mitigates the greenhouse effect.3D-mesoporous KIT-6 was modified by ethylene glycol,which facilitated the formation of small Ni nanoparticles.Compared with other preparation methods,Ni/KIT-6?EG?exhibited a better catalytic performance at 250⁵00^oC,atmospheric pressure and 96000m L/g/h and the maximum value for CO₂ conversion was 72.3%at 450^oC.Ni/KIT-6 was further modified with various promoters?Mg,V,Ce,La?.V species exhibited the best promoter effect for CO₂ methanation,and the selectivity of CH₄ below 400°C remained at 100%,and CO₂ steady-state conversion was achieved up to 75.4%at400°C.The effects of V and Ni contents on the catalytic performance were investigated with further optimization.Among all the catalysts,20Ni-0.5V/KIT-6 exhibited the best CO₂ catalytic performance with 87.2%of CO₂ conversion and 100%of CH₄selectivity at 350^oC.Moreover,the effects of reaction temperature,space velocity and H₂/CO₂ on the catalytic performance of CO₂ methanation with 20Ni-0.5V/KIT-6 were also investigated.Typically,coal-fired flue gas components are more complex,consisting of CO₂,N₂,O₂,H₂O,sulfide and nitride.For the CO₂ from coal-fired flue gas,it is necessary to take the absorption separation and then conversion and utilization during the hydromethanation reaction.During the process of 320^oC isothermal CO₂ absorption and catalytic conversion,the suitable carrier and active metal were selected for TH100and active metal Ru,respectively.The CO₂ absorption properties on La/Ba/Mg materials with various contents were explored,and the material with 10wt%La₂O₃was the best,corresponding to TGA result for 0.29wt%and activity test result for 0.97mol/kg,while the dual functional material?DFM?containing 10wt%La₂O₃ showed better CO₂ absorption and catalytic conversion performance.After addition of Ca species,La and Ca exhibited the best synergistic effect when the content of CaO was5wt%and the CO₂ absorption performance was 1.52mol/kg.The weight loss on the DFM with La-Ca for CO₂ absorption and methanation in the TGA test were 1.27wt%and 1.28wt%,respectively,and exhibited good stability performance after ten hydrogenation cycle stability test.