Research On Catalysts Of CH₄ Dry Reforming In A Fluidized Bed Reactor

CH₄-CO₂ reforming has attracted much attention for its great significance toward sustainable development of energy.Although a large amount of researches have been displayed to improve the activity and stability of catalysts,the of catalyst deactivation and reactor block originated from severe carbon deposition have not been solved yet and it still needs further research to make it applicable to industrial use.Among various kinds of catalysts,Co/MgO catalyst is highlighted for its excellent performance of reaction activity and stability while it can suppress carbon deposition due to the exposed（111）crystalline face of MgO which strongly absorbs CO₂.However few literatures have illustrated the deactivation mechanism and carbon deposition behavior of Co/MgO.Compared to fixed bed reactor,fluidized bed reactor exhibits lower pressure drop and higher efficiency of mass and heat transfer which can get rid of reactor block.However only a few researches are based on CH₄-CO₂ reforming in fluidized reactor where the quality of fluidization of catalyst particles should be taken into consideration.In this research,Co-based catalysts loaded on MgO carriers are evaluated in a fluidized bed reactor while the innovative discoveries are listed as follow:（1）The research of Co/MgO catalyst prepared by impregnation has proved that the initial deactivation of catalyst coming up with significant carbon deposition is mainly resulted from Co metal oxidization.During the reforming reaction,oxygen species from dissociated CO₂ combine with metallic cobalt which suppresses carbon elimination process.Followed by the formation of multilayered carbon（CNOs）coating on the surface of Co,the quantity of layers increases with the extent of metal oxidization till totally blocking the active center and leads to catalyst deactivation.（2）Co@MgO catalyst with diameter in micrometer scale has been prepared by hydrothermal method.Compared with Co/MgO loaded on commercial MgO carrier,Co@MgO exhibits better fluidization quality and higher BET and dispersion as well as better performance of activity and stability.（3）Fluidization quality and reaction activity are tested with and without the assistance of magnetic field.Fluidization test indicates the magnetic field reduce the bubble size and improves gas-solid contact efficiency while U_mf measured by fluidization method does not change.Stability tests under 700℃and 800℃show that the reactant conversion is higher（⁵%higher under 800℃）with magnetic field.Characterization of used catalysts show that the I_D/I_G ratio in magnetic field bed is much higher than fluidized bed indicating the introduction of magnetic improves the mass transfer efficiency and suppress the transfer from C_β to C_γ.