Studies Of Nickel-Based Catalysts Modified By Lanthanum Oxide For Carbon Dioxide Reforming Of Methane

The production and life in modern society rely on fossil energy to a great degree,and the search for feasible ways to achieve CO₂ utilization can help alleviating the problems of greenhouse effect and energy shortage.Carbon dioxide reforming of methane（CRM）is one of the most promising ways to achieve CO₂ utilization.It converts two main greenhouse gases（CO₂ and CH₄）into syngas with H₂/CO ratio close to one,which can be directly used as raw materials for the Fischer-Tropsch synthesis.However,many difficulties and challenges are still existed in CRM reaction,and the most important thing is the sintering and carbon deposition leading to deactivation.Studies have shown that the morphology,promoters and preparation methods of the catalysts have a profound impact on the catalytic performance.In this thesis,nickel-based catalysts modified by lanthanum oxide were investigated for the CRM reaction.The effects of La2O3 modification,Ni loading,solvent and catalyst morphology on the catalytic performance of the catalysts were investigated,and their impact on catalyst basicity,particle size and metal-support interaction were analyzed in detail.In the first part,based on the KIT-6 molecular sieve with large specific surface and rich pore structure properties,the Ni/La2O3/KIT-6 catalysts with different loadings were prepared by using the basic promoter La2O3.The characterization results showed that the La₂O₃ improved the metal-support interaction,promoted the dispersion of Ni nanoparticles and inhibited the sintering.At the same time,the La2O3enhanced the CO₂ adsorption and activation ability of the catalysts,which was beneficial to inhibit carbon deposition and improve catalytic performance of Ni-based catalysts.Among them,catalyst 6%Ni/10%La2O3/KIT-6 exhibited the highest catalytic activity,and showed the best catalytic stability in the CRM tests.In the second part,three different morphologies of LaNiO₃ perovskite catalysts were prepared by sol-gel method.The effects of catalyst morphology on catalytic performance were compared,and the effects of perovskite structure and catalyst morphology on particle size and dispersion of Ni nanoparticles were analyzed.The characterization results showed that the perovskite structure promoted the dispersion of Ni particles and inhibited the migration of Ni particles,and the pore structure limited the growth of Ni nanoparticles.At the same time,the strong interaction of metal and support inhibited the sintering of nanoparticles.After the catalyst reduction,the lanthanum species enhanced the basicity of catalysts,and promoted conversions of the reactants and inhibited carbon deposition.Among them,the porous structure of the perovskite LaNiO3 catalyst made it outstanding in suppressing sintering and inhibiting carbon deposition and eventually showed better catalytic performance for CRM reaction.Compared with the reported Ni/SBA-15 catalysts,the La2O3 promoter and KIT-6support further improved the metal-support interaction,promoted the dispersion of Ni particles and inhibited the sintering of Ni particles.At the same time,La2O3 enhanced the adsorption and activation ability of the catalyst for CO2,alleviated carbon deposition,and improved catalytic performance.In addition,the catalytic performance is also related to the amount of La2O3 modification,morphology and preparation.And compared with the reported bar Ni/La2O3 catalysts,the porous structure of the perovskite LaNiO3 catalyst made it possessing higher BET surface area and stronger structure stability,enhanced the advantage of La2O3 greatly,promoted the dispersion of Ni particles and inhibited the sintering of Ni particles,and improved catalytic performance.