The Study On Ethanol Steam Reforming Over Molecular Sieve SBA-15 Supported Cobalt Catalyst

As a high efficient and clean energy, hydrogen can solve the environmental problem and energy crisis, with the growing of application field hydrogen, it is very necessary for developing. Ethanol steam reforming(ESR) is becoming a hot topic of hydrogen production and has a good application prospect for its high hydrogen yield and good reaction efficiency. Mesoporous molecular sieves SBA-15, has large surface area, regular pore structure, large pore size and good thermal stability. The above advantages make SBA-15 has a good prospect in the catalysis field. Nowadays, metals loading into the channels of the support SBA-15 in order to prepare high active catalysts have received extensive concern of researchers.In this paper, we used mesoporous molecular sieves SBA-15 as support, first with cobalt nitrate as cobalt source, by incipient-wetness impregnation method to prepare Co/SBA-15 catalyst with different Co loadings. The catalysts were characterized by XRD, N2 adsorption, H2-TPR,TG and FT-IR, the results showed that catalysts after loading Co maintained the mesoporous structure well and mainly existed on the surface or inside the pore of SBA-15. After reaction, it showed that the loading content effect the reaction results. Hydrogen selectivity isn’t increased monotonically with the cobalt loading increasing. Hydrogen selectivity became lower when cobalt content increased to a certain extent, for the reason of the accumulation and reunite of cobalt. After compared with other catalysts, 10wt% Co loading catalyst at reaction temperature of 550℃ was found to be the best catalytic performance.In order to study the change of the cobalt active sites during the reaction, we prepared Co/SBA-15 with 10wt% loading. And then were reduced under a flow of H2 with different reduction temperature. Through X-ray diffraction, it was showed the catalyst was mainly composed of Co3O4 after calcined, but after reduction at 300℃ the main composition went to Co O. With the increase of the reduction temperature, CoO transforming into metallic cobalt. The result of catalytic activity exhibited that coexistence of CoO and metallic cobalt can get higher hydrogen selectivity and ethanol conversion. When the catalyst was reduced at 400℃, the selectivity of H2 reached 68.40% and the conversion of ethanol went to 93.49%. So we draw a conclusion that the main active site of the catalyst is metallic cobalt with CoO.Chose cobalt nitrate, cobalt sulfate, cobalt chloride and cobalt acetate as cobalt source, prepared four different Co/SBA-15 catalysts with 10wt% loading respectively. Catalysts characterization showed that after calcined, catalysts prepared by cobalt nitrate, cobalt chloride and cobalt acetate only showed Co3O4 while cobalt sulfate showed CoSO4. After reduced at 400℃, there were CoO and metallic cobalt coexisted in nitrate and cobalt acetate prepared catalysts, but Co SO4 still existed except metallic cobalt in cobalt sulfate prepared catalyst. There was found carbon in cobalt acetate prepared catalyst. The stability test showed that due to the problems as deposition of carbon, compared with catalyst prepared by cobalt nitrate, other catalysts’ performance is not very good and catalyst prepared by cobalt nitrate had the best performance.