Preparation And Performance Study Of Catalysts For Catalystic Steam Reforming Of Rice Straw To Hydrogen-rich Syngas

Thermal cracking and gasification of biomass to H₂-rich syngas not onlycan make effective use of the abundant biomass resources but also canimprove energy efficiency. However, the quality of traditional biomassgasification gas product is not high, the gas product usually containsunacceptable levels of tar, and excessive tar not only reduces the overallgasification efficiency but also has a negative impact on the composition ofsyngas. Pyrolysis gasification with steam is a process which can solve theabove problems.A series of Ni-based catalysts with different supports （TiO₂, CaO, SiO₂and γ-Al₂O₃）, of which Ni content were from2.5wt%-15.0wt%, were preparedby an incipient wetness impregnation. And Ni-based catalysts with γ-Al₂O₃assupports and Co, La, Ce, Ca, Mg as promoter were also repared, of which Nicontent were7.5wt%. By using target biomass agricultural waste rice straw,the performance of catalytic steam reforming of rice straw converting into thehydrogen-rich syngas was tested in a fixed-bed reactor. The various factors of influencing the generation of syngas, such as Ni content, steam/biomassratio（S/B）, biomass/catalyst mass ratio （B/C）, space velocity and reactiontemperature were investigated. The structure of the catalysts was characterizedby X-ray diffraction and N2adsorption-desorption, some new experimentalachievement were obtained as the following:Catalysts with γ-Al₂O₃as support showed better activity compared to theother three Ni-based catalysts with different supports （CaO, TiO₂and SiO₂）.Among which, the hydrogen yield over7.5%Ni/γ-Al₂O₃catalysts reached1071.3ml H₂/g biomass, H₂volume fraction reached33.2%, H₂/CO ratiowas1.4. The optimum reaction conditions were S/B ratio2.02, B/C ratio5, andreaction temperature820℃. The excellent catalytic activity of Ni/Al₂O₃catalysts may due to the surface acidity of γ-Al₂O₃which may promote tarcracking reaction, the interaction between Ni and γ-Al₂O₃which promoted theendothermic reforming reaction.As for the Ni-based catalysts with γ-Al₂O₃as supports, Ni content7.5wt%, Co, La, Ce, Ca, Mg as promoters, the addition of Mg improved thecatalytic activity significantly. Among them1.0%MgO-7.5%Ni/γ-Al₂O₃catalysts showed the best catalytic activity, the hydrogen yield over themreached1194.6ml H₂/g biomass, the H₂/CO ratio reached5.2, which not onlycan improve the hydrogen yield but also can generate more H₂-rich syngas. Onone hand, the addition of Mg to Ni/γ-Al₂O₃catalysts can improve the steamcatalytic reforming of rice straw to syngas; on the other hand, it can improve the water-gas shift reaction in the process of catalytic reforming which thengreatly improved the hydrogen yield and H₂/CO ratio. According to thestructure characterization of catalysts, the addition of Mg improved thespecific surface area of catalysts.