Preparation Of Co₂C-based Catalysts For Low-temperature Water-gas Shift Reaction

Water-gas shift reaction?WGSR?is mainly used for preparation of hydrogen and is also widely applied in industrial processes such as ammonia synthesis,methanol synthesis,hydro-refining,hydrocracking,and Fischer-Tropsch reactions.The traditional WGSR catalysts in industry include Fe-Cr high-temperature shift catalyst,Cu-Zn-Al low-temperature shift catalyst and Mo-Co sulfur-tolerant wide-temperature shift catalyst.However,the Cr in the Fe-Cr catalyst is a highly toxic substance.Cu-Zn-Al catalyst exhibits poor thermal stability.The pretreatment process of Mo-Co catalyst is rather complicated.These shortcomings limit the further applications of traditional catalysts.To meet the requirement of new industrial processes,it is necessary to develop high-performance water-gas shift catalysts at mild reaction conditions.Herein,Co₂C-based catalysts were prepared and tested for low-temperature water-gas shift reaction.The active phase and structure-performance relationship were investigated in detail.The research progress was summarized as following.1.Development of Co₂C-based low-temperature water-gas shift catalyst and study of structure-performance relationshipCo₂C-based catalyst was prepared and exhibited promising catalytic performance for low-temperature water-gas shift reaction.CO conversion reached up to 40%while the CO₂ selectivity was 100%at 220?.The effect of reaction conditions,including reaction temperature,weight hourly space velocity?WHSV?and H₂O/CO ratio on catalytic performance was studied in detail.CO conversion increased with the increase of reaction temperature and H₂O/CO ratio,while CO conversion sharply decreased with the increase of WHSV.However,there was no obvious change for the CO₂ selectivity.In addition,the effect of reduction temperature on the catalytic performance and catalyst structure was also investigated.The catalysts reduced at 250?and 300?exhibited high activity.In contrast,low activity was found for the catalysts reduced at 350?and400?.According to the structure characterization,low reduction temperature benefited for the formation of small Co₂C nanoparticles with high activity.With the increase of reduction temperature,metal Co with larger particle size was obtained and led to the formation of larger Co₂C nanoparticles with low activity.2.Effect of Mn on Co₂C-based WGSR catalystThe addition of Mn exhibited a profound effect on the catalytic performance and catalyst structure of Co₂C-based catalyst.With the increase of Co/Mn ratio from 1 to20,CO conversion gradually increased and reached 52.6%at 220?for Co20Mn1catalyst.However,the activity of per unit mass Co increased to the maximum and then decreased.The Co2Mn1 catalyst exhibited the highest specific activity with 97.5 mMol CO/h·g Co at 220?.The catalyst structure was studied via XRD,TPR and TEM.CoMn composite oxides existed in calcined and reduced samples.The particle size of spend catalysts was obviously higher than that of the fresh catalysts.According to the TEM result,Co₂C nanoprisms were observed when Mn was added.Combining the result of catalytic performance and structure characterization,the Mn could promote the formation of Co₂C nanoprisms.In addition,the addition of Mn benefited for the dispersion of Co and led to small Co₂C nanostructures with high activity.3.Effect of metal promoters on Co₂C-based WGSR catalystThe effect of metal promoter on Co₂C-based WGSR catalyst was investigated.The addition of noble metal?Au,Pd,and Ru?promoted the catalytic performance of Co₂C-based catalysts.However,the addition of Cu inhibited the catalytic activity.Among the noble metal,the addition of Au showed the best promotion effect.However,serious sintering for Au nanoparticles occurred for the Au-promoted catalyst prepared by impregnation method,which led to catalytic deactivation.Therefore,it is necessary to find new methods to avoid Au agglomeration and further improve the catalytic performance.