Perovskite Oxides Supported Cobalt Catalysts For Steam Reforming Of Ethanol To Produce Hydrogen

Hydrogen, as an efficient and environmentally-friendly energy carrier, hasreceived high attention from the people in the last century. Hydrogen fuel cell hasbeen widely concerned by the world with its efficient and pollution-free features.Steam reforming of ethanol (SRE) has become an important way of hydrogengeneration from ethanol for its high efficiency of hydrogen production and wide rawmaterial sources. The hydrogen obtained can be used as the hydrogen source of fuelcell through a series of purification. Sintering and carbon deposition are the keyproblems ought to be solved, which may affect the stability of catalysts for hydrogenproduction in SRE. According to the known research reports, the catalytic activity andselectivity of the majority of catalysts can meet the requirements of practicalapplications, but we still need to improve the stability of catalysts (namely, to solvethe sintering and carbon deposition problems) and reduce costs. Cobalt and nickelcatalysts have good C-C fracture ability, exhibit high activity and selectivity ofethanol reforming. But both of them present the sintering, oxidation and carbondeposition of active metals. Because the two metals interact on the surface of thecarrier to restrain the growth of metal particles, bimetallic catalysts have goodsintering and carbon deposition resistance properties, which is beneficial forincreasing the stability of catalysts. Perovskite has good adjustable degeneration,thermodynamic stability and chemical stability and it can improve the dispersion ofthe active ingredients and form interaction with them. In addition, the oxygenvacancies of the perovskite can inhibit the production of carbon deposition and reducethe activity of active ingredients, thus improve the stability of catalysts. Combiningthe structural properties of the perovskite with the catalytic activity characteristics ofCu, Co and Ni, the paper adopts the impregnation and citric acid complex method toprepare single metallic and bimetallic perovskite-type catalysts with good activity,selectivity and stability, and uses them for SRE, as well as studies the existence formof active ingredients, structure of carriers and relationship between catalytic propertiesand structures.Based on structural properties of the perovskite, the La1-xCaxFe1-xCoxO3catalystis prepared by the citric acid complex method, compared with the steam reforming ofethanol and ethanol oxidation reforming reactions, and characterized by means ofTPR, XRD, XPS and TEM. Results show that Co3+in La1-xCaxFe1-xCoxO3is reduced to metal particles which are highly dispersed on the surface of the perovskite carrierunder reducing atmospheres, when the reduced catalyst is oxidized again, the highlydispersed nano-Co particles will return to perovskite lattice so as to achieveregeneration of catalyst and thus increase the stability of catalyst. TheLa0.7Ca0.3Fe0.7Co0.3O3catalyst shows good catalytic activity and stability when it isused for OSRE reaction, which is maybe due to the fact that nano-Co particlesproduce internal and external circulations in perovskite lattice and inhibit the sinteringand carbon deposition generation of Co particles.Based on structural properties of the perovskite and good activity of steamreforming of ethanol of Cu and Co, the Cu-Co perovskite-type bimetallic catalysts(Co/LaFe0.7Cu0.3O3and Cu-Co/LaFeO3) are prepared by the citric acid complex andimpregnation method, and characterized by XRD, TEM, TPR and TG/DTA. Resultsshow that Co/LaFe0.7Cu0.3O3catalyst forms Cu-Co alloys which are highly dispersedon the surface of the perovskite carrier after being reduced successively, whileCu-Co/LaFeO3catalyst does not form alloys and Cu and Co are independentlydispersed on the surface of the carrier. The locations of the carrier where Cu and Codispersed are different and the existence forms of Cu and Co after reduction are alsodifferent. Through SRE catalytic activity tests, the two types of catalysts have goodreforming activity but more serious carbon deposition, which is maybe related to theeasier carbon deposition generation of Cu.Combined with good ethanol reforming activity of Co and Ni and structuralproperties of the perovskite carrier, the perovskite supported bimetallic catalystNi/LaFe0.7Co0.3O3and single metallic catalysts Ni/LaFe0.7Ni0.3O3andCo/LaFe0.7Co0.3O3are prepared by the citric acid complex and impregnation methodto be used in hydrogen production from steam reforming of ethanol reaction, andcharacterized by TPR, XRD, TEM and TG/DTA. Results show that Co and Ni formalloys after reduction, and the experiment result shows that this catalyst has goodcatalytic activity and stability. The bimetallic catalyst has better anti-sintering abilitythan that of single metallic catalyst, which is maybe due to the fact that Co and Niproduce synergistic action and form Co-Ni alloys and improve the stability andanti-sintering ability of catalyst according to characteristics of the carrier.