Preparation And Reaction Investigation Of Catalysts For Catalystic Steam Reforming Of Biomass To Hydrogen-Rich Syngas

Hydrogen is regarded as the energy for future with its cleanness and high calorific value and has become a focus of renewed interest in many parts of the world. As the fossil energy resource reduces sharply and the pollution of the environment becomes more serious, biomass has been considered as one of the most probable source for hydrogen production. The number of disused biomass proved to be enormous in our national city. Coversion from this part of biomass to hydrogen-rich syngas using an effective catalyst and gasifying agent is thought to be a feasible option. This production pathway is an environmentally clean and economically viable solution which results in scarcely any CO2 emissions with greenhouse effect. Gasfication of biomass often results in heavy tar and low hydrogen yield in gas product. These two notable problems confine the varity use of gas production to application. Stream has been recognized as a effective gasifying agent for tar removal and higher hydrogen yield. It is investigated that Ni-based catalyst has been recognized as an effective catalyst with high activity for catalytic steam reforming from biomass to hydrogen.In this paper, the poplar leaves biomass materials as the feedstock for the steam reforming were collected and ground to powder. The proximate analysis and ultimate analysis of biomass sample were made as well as TGA. A series of Ni-based SBA-15 catalysts with Ni content from 5wt% to 20wt% and the modifications with alkaline earth metal (Mg, Ca, Sr, Ba), rare earth metal (La, Ce) and transition metal(Co) were prepared by impregnation method. A great many factors affected the performance of catalytic steam reforming of the poplar leaves to the hydrogen-rich syngas was investgated in fixed-bed reactor under atmospheric pressure, such as temperature, steam flow, Ni content, mass ratio of biomass and catalyst. The structure of catalysts was characterized by X-ray diffraction (XRD), N2-adsorption/desorption, transmission electron microscopy (TEM).The results indicated that the 12.5wt%Ni/SBA-15 catalyst exhibited the best performance for the catalytic steam reforming of poplar leaves to hydrogen-rich syngas. A maximum hydrogen yield and hydrogen volume fraction among gas products was observed to 158.50 ml H2/g biomass and 31.08% under the optimal reaction conditions that reaction temperature was 800℃, steam flow was 60ml.h-1, biomass/catalyst mass ratio was 5. It could be acquainted with the fact that the prepared molecular sieves SBA-15 maintained a good meso-porous structure and the structure of SBA-15 modified by Ni kept in good condition. The interaction force between active component and carrier was moderate, which promoted the catalystic reforming. Noteworthily, CaO-12.5%Ni/SBA-15 catalysts exhibited the highest performance among the series of M/Ni/SBA-15 catalysts. It was indicated that the CaO content of 7wt% favored the maximum hydrogen production which increased to 273.30 ml H2/g biomass and 54.5% in volume under the same condition. The addition of MgO also largely improved the product distribution and gas quality of poplar leaves. Hydrogen yield reached 272.85ml H2/g biomass and hydrogen volume fraction to 57.05%. Both addition of CaO and MgO promoted the reaction to a finer performance.1 g biomass generated 321.16ml H2. In the meantime, hydrogen volume fraction reached over 60%.The addition of CaO and MgO improved the product distribution and gas quality of poplar leaves, resulting in the decrease of CO. Future investigation suggested that the addition of CaO increased the dispersity of NiO and CaO was in a high degree of disparity. Meanwhile, molecular sieves SBA-15 maintained a good meso-porous structure with the modification of CaO. CO2 was absorbed by CaO and largely lowered in the gas system. In the presence of excessive steam, the free energy of Gibbs of system declined substantially, which played a promotive role in pushing water-gas shift reaction. It changed the original equilibrium of gas phase and pushed water-gas shift reaction to take place on the direction of hydrogen production to produce the additional H2.30% CO2 was absorbed while CaO content increased to 7wt%, which attributed to the limited capability of CaO for CO2 absorption under high temperature. CaO played the role not only of a CO2 sorbent but also that of a catalyst for biomass gasification.