The Study On Co/CeO₂ Catalysts For Steam Reforming Of Ethanol

Catalyst stability is a crucial problem for hydrogen production in steam reforming of ethanol (SRE), which can be caused by carbon deposition, metal sintering, and so on. CeO₂ has a good oxygen-storage capacity and tends to interact with active component. The presence of CeO₂ is benefit for carbon oxidation and adjusting chemical nature of active component. These would improve catalyst stability. In our work, new Co/CeO₂ catalysts for SRE were studied. The study included catalyst structure, catalytic performance and the relation of preparation method with structure and catalyst performance. Besides, the carbon deposition and the effect of support were also investigated on the Co/CeO₂ catalysts for SRE.The Co/CeO₂ catalysts were prepared by co-precipitation. The research indicates that cobalt exists in three forms including cobalt oxide with small crystal size, bulk Co3O4, and cobalt in CeO₂ lattice in these catalysts. Both the content of cobalt and calcination temperature affects the form of cobalt. Combining with activity test, metal cobalt reduced from high dispersion oxides of cobalt with small crystal size is crucial active component. The 10%Co/CeO₂-650 catalyst prepared by co-precipitation method shows high activity, selectivity and good stability.The Co/CeO₂ and Co/CeXTi1-XO₂ catalysts were prepared by impregnation method. They show higher selectivity towards methane than Co/CeO₂ prepared by co-precipitation method. It shows that the addition of Ti does not improve catalyst performance. Ti may interact with Ce or Co, and weaken the interaction between Co and Ce, so it results in the decrease of catalytic performance. In addition, XRD results show that only Co3O4 and CeO₂ phases can be observed in the Co/CeO₂ catalysts prepared by impregnation method. So the chemical nature of cobalt in the catalysts is affected obviously by preparation method. The 20%Co/CeO₂-I-650 catalyst prepared by impregnation method also shows good catalytic performance for SRE.The effect of preparation method on catalyst structure, reduction capability and catalytic performance was investigated. The results indicate that the synergistic effect exists between cobalt and CeO₂, which influences the reduction of CoOx. Co0 reduced from CoOx is key active component. The preparation method influences the interaction between cobalt and CeO₂. In comparison with catalysts prepared by impregnation, more Co ions enters into CeO₂ lattice, and results in weaker interaction between active phase and ceria on surface of Co3O4/CeO₂ prepared by co-precipitation. Thus, it is easier to reduce Co species to metal cobalt that is active for SRE. Meanwhile, the incorporation of Co ions into CeO₂ crystal lattice is beneficial for resistance to carbon deposition.The impact of reaction temperature and reaction time on carbon deposition was researched on 10%Co/CeO₂-650 catalyst with co-precipitation method. Combining with DTA-TG and SEM study, the discipline between the quantities of carbon deposition and carbon species was analyzed.The feasibility of Al2O3 as carrier for hydrogen production was investigated in SRE. Further, the effect of Al2O3 on catalyst structure and performance was studied.