The Study On Ni/Ce-M-O (M=Zr, Ti, La) Catalysts For Steam Reforming Of Ethanol

The crucial issue for hydrogen production by steam reforming of ethanol (SRE) is to develop efficient catalysts. The critical challenge for SRE catalysts is to improve stability and low temperature activity. CeO₂-based oxides are characterized with good oxygen-storage capacity and tend to interact with active component, which is beneficial for eliminating carbon and adjusting chemical nature of active component. In this work, a series of Ni/Ce-M-O (M=Zr, Ti or La) catalysts for SRE were studied, which exhibited high low temperature activity and good stability for SRE. The relation between catalyst structure and catalyst performance was also investigated.The Ni/Ce_0.5Zr_0.5O₂ catalysts were prepared by citric complexing method. The effects of preparation conditions and reaction conditions on catalytic performance were investigated. The results indicated that 20%Ni/Ce_0.5Zr_0.5O₂-700 catalyst was very active and selective at low reaction temperature under the space velocity of 160,000ml·h^-1·gcat^-1 and the metal nickel reduced from NiO in strong interaction with support is the key active species. TG-DTA and XRD results show that 20%Ni/Ce_0.5Zr_0.5O₂-700 catalyst exhibits high anti-sintering and good carbon-resistance quality.Ni/CeO₂-TiO₂ catalysts prepared with impregnation method showed good catalytic performance for SRE. Experimental results indicate that the content of nickel, the molar ratio of Ce/Ti and calcination temperature have influence on catalysts phase structure and the interaction between Ni species and support, and thus affect catalytic performance obviously. The high activity of Ni/CeO₂-TiO₂ catalysts is ascribed to the metal nickel reduced from NiTiO3, which is highly dispersed with good anti-sintering ability. The good stability for carbon deposition resistance of this catalyst is mainly attributed to the formation of Ce-O-Ti solution which can improve oxygen mobility in the support. Among the catalysts tested in this series, 10%Ni/Ce_0.5Ti_0.5O₂-700 exhibits the best catalytic performance.The 10%Ni/La-Ce-O catalyst prepared by citric acid method shows comparatively good carbon-resistance ability at 450℃due to its high redox capability, which was originated from the formation of La-Ce-O solid solution and the interaction between nickel species and carrier. The possible reaction pathways over 10%Ni/La-Ce-O are proposed. By comparison, the addition of Zr, Ti or La has effectively improved the dispersion of NiO, the interaction between active species and support and the redox capability of CeO₂, which results in the improvement of catalytic performance of Ni/CeO₂ catalyst for SRE. The forms of nickel species in Ni/Ce_0.5Zr_0.5O₂ and Ni/Ce_0.55La_0.45O_x catalysts are similar, but the different proportion of various nickel species in two catalysts leads to a big change of products selectivity in SRE. The high activity for SRE of Ni/Ce_0.5Ti_0.5O₂ catalyst originated from metal nickel reduced from small particle NiTiO3. In addition, experimental results indicate that Ni/Ce_0.5Zr_0.5O₂ and Ni/Ce_0.5Ti_0.5O₂ catalysts are fit for high temperature reaction and that Ni/Ce_0.55La_0.45O_x catalyst prefers to be applied in low temperature.