Hydrogen Production From Steam Reforming Of Ethanol Over Co/CeO₂Catalysts

Hydrogen is a clean, efficient and renewable energy. The most attractive andpromising technology of hydrogen is its application in fuel cell. Cobalt-basedcatalysts have attracted lot s of attention due to their low cost, high activity and betterselectivity in steam reforming of ethanol. However, the sintering and oxidation of themetal cobalt particles, and carbon deposition would lead to the deactivation ofcobalt-based catalysts; as a result, the stability of catalysts needs to be furtherimproved. CeO₂owns excellent oxygen-storage capability, and CeO₂is easy to haveinteraction with the supported metal, both of which will improve the stability ofcatalyst. In this paper, we focus on the modification of Co/CeO₂catalyst. We studiedthe nature of support and the precursor of active component cobalt respectively,aiming to improve the oxygen storage capacity of the catalyst carrier as well as theinteraction between metal and support, thus the stability of the catalyst could beimproved.First, we looked into the influences of CeO₂morphology on the catalyticperformance of Co/CeO₂. CeO₂with different morphology were synthesized byhydrothermal methods. TPR results show that CeO₂nanorods owe the highest oxygenstorage capacity while the interaction between CeO₂nanoparticles and the supportedmetal is the strongest. However, the ethanol conversion over10%Co₃O₄/CeO₂NR isnot as perfect as we thought owing to the smaller surface area of CeO₂nanorods. Thebetter oxygen storage capacity of CeO₂nanorods would benefit the oxidation ofcarbonaceous products.Then, the influences of praseodymium doping on structure of catalyst andcatalytic performance for SRE were investigated. Co₃O₄/Ce_1-xPr_xO₂catalysts wereprepared by co-precipitation method and used for steam reforming of ethanol （SRE）to produce hydrogen. The best preparation conditions are: the weight content ofCo₃O₄is15%, and the molar ratio of Ce: Pr=0.8:0.2, over which the completeconversion of ethanol could be reached at T=400℃. XRD, TPR, thermal analysis andTEM results indicate that the incorporation of Pr would decrease the diameter ofCo₃O₄particles in the catalysts and would intensify the interaction between Co₃O₄and support, both of which improve the anti-sintering stability of metal cobalt.Besides that, adding of Pr into ceria favors the generation of oxygen vacancies incatalyst, which contributes to the improvement of anti-carbon deposition property. The incorporation of Pr would also have influence on the nature of carbon depositionFinally, we studied the Co/CeO₂catalyst from the perspective of the precursor ofactive component. We proposed CeO₂supported LaCoO₃perovskite-type catalysts.The best preparation conditions of this series are: the weight content of LaCoO₃is20%, and the calcination temperature of LaCoO₃is650℃, over which the100%conversion of ethanol could be achieved at T=600℃, the hydrogen selectivity is over65%. XRD results showed that all catalysts showed characteristic diffraction peaks ofLaCoO₃and CeO₂without characteristic diffraction peaks of individual Co₃O₄andLa₂O₃. After the pre-reduction treatment, LaCoO₃perovskite structure was destroyedand cobalt particles with smaller particle size were generated which were highlydispersed on the support. At the same time, La₂O₃generated from the reduction ofLaCoO₃would interact with CeO₂（some La3+would incorporate into the lattice ofCeO₂）, which would favor the elimination of carbon deposited on the catalyst surface.