Study On Supported Ni-Ru Bimetallic Catalysts For Hydrogen Production From Ethanol Steam Reforming

Ethanol can be prepared from fermentation of agricultural residues and hence it is a renewable resource. Its production is simple and cheap and hence steam reforming of ethanol to produce hydrogen is attractive more and more. Ni-Ru bimetallic catalysts were prepared using impregnation method and the catalytic properties for hydrogen production from ethanol steam reforming were investigated in this thesis. The effects of different ratio of Ni-Ru, different supports and different ratio of metal oxide in composite support on catalytic properties of bimetallic catalysts were discussed. The catalysts were characterized by means of nitrogen adsorption-desorption, H₂ temperature programmed reduction(H₂-TPR), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and thermo gravimetric(TG) to study BET surface area, redox properties, phase structure, surface composition and valence and resistance to carbon deposition. The applications of Ni catalysts prepared by a plasma treated method in ethanol steam reforming were studied primitively. The influence of plasma treatment on phase of catalysts, redox properties and catalytic activities were investigated.In Ni-Ru/ZnO bimetallic catalysts Ni-Ru alloy maybe formed in the catalysts and the reduction of ruthenium oxide enhanced reduction of nickel oxide. Ni-Ru alloy existed in the bulk phase not on the surface of the catalysts. Activity test proved that the ability of Ni for rupture of C-C bond was stronger than that of Ru, and Ru was active in the ethanol dehydration reaction leading to the formation of ethylene. However, Ru could improve the selectivity of hydrogen. The catalyst with metal loading of 6wt%Ni and 3wt%Ru showed best performance. The ethanol conversion could reach 100% at 400℃. And CO selectivity was minimum of 0.41% at 450℃while the selectivity for hydrogen was 77.2%.The precursor of La was La₂(CO₃)₃ whereas XRD exhibited that La was in the form of hexagonal La₂O₂CO₃ in Ni-Ru bimetallic catalysts and there existed mixed oxide of Ni and La. The lattice oxygen existed on the surface of the catalysts supported on La₂O₂CO₃, which was benefit for improvement of catalytic activity and hydrogen selectivity. As ZnO supported catalyst, the catalyst with metal loading of 6wt%Ni and 3wt%Ru supported on La₂O₂CO₃ showed best performance. The ethanol conversion could reach 100% at 400℃, and CO selectivity was minimum of 0.87% at 450℃while the selectivity for hydrogen was 85.9%. Ni-Ru bimetallic catalysts supported on La₂O₂CO₃ could decrease the amount of carbon deposition and improve the stability of catalysts.ZnO-La₂O₂CO₃ mixed supports were prepared using impregnation method. The effect of different molar ratio of Zn and La in supported 6wt%Ni-3wt%Ru bimetallic catalysts on the catalytic performance was discussed. The results showed that the catalyst with molar ratio of Zn: La=1:2 performed best. The ethanol conversion was 100% at 400℃, and CO selectivity reached minimum of 0.57% at 450℃while the selectivity for hydrogen was 87.8%. XPS studies exhibited that lattice oxygen could be enriched on the surface of composite support compared with mono support. XRD and TPR showed that mixed oxide of nickel and lanthanum was formed and the integrity of lattice for hexagonal ZnO and La₂O₂CO₃ was damaged.Catalysts Ni/ZnO and Ni/La₂O₂CO₃ were prepared using plasma enhanced impregnation method. The phase of catalysts did not change after plasma treatment whereas the particle size of metal oxide could be decreased. TPR results exhibited that the interaction between metal and supported didn't be changed greatly but the distribution of NiO was improved. The activity and hydrogen selectivity on Ni/ZnO prepared using plasma enhanced impregnation method were improved. However, the ethanol conversion decreased at low temperature and at a high temperature hydrogen selectivity decreased on the plasma-treated Ni/La₂O₂CO₃.