Preparation And Performance Investigation Of The Catalysts For Syngas Production Via Biogas From Municipal Solid Waste

A large volume of biogas,whose main constituent are methane and carbon dioxide with a volume ratio of about 2:1,could be production through an anaerobic digestion process from municipal solid waste.So the syngas production could be carried out by adding appropriate volume of steam to the biogas.It is not only a promising untilization of the municipal solid waste,but also a reduction of greenhouse gas exhausts.And the key work for the realization of this method is the development of a novel catalyst with excellent catalystic performance and diathermancy.In this paper,a series of Ni/SBA-15 catalysts with Ni loadings from 5wt%to 15wt%were prepared by impregnation method.For the improvement of the catalystic performance,modifications were also done with alkali or alkaline earth metal oxides,rare earth metal oxides,transition metals and Ce_xZr_1-xO₂.For the enhancement of their diathermancy,Ni/SBA-15/Al₂O₃/FeCrAl catalysts and Ni/M/SBA-15/Al₂O₃/FeCrAl(M=La₂O₃,MgO,Ce_xZr_1-xO₂) catalysts were also prepared.Finally,their catalystic performances were investigated,and their structures were also characterized by XRD,H₂-TPR and CO₂-TPD techniques.The catalysts with 10wt%Ni loading had a best catalystic performance. Under the reaction conditions:T=850℃,CH₄:CO₂:H₂O=-2:1:1.5 and GHSV=2.70×10⁴ ml g_cat^-1h^-1,over the 10wt%Ni/SBA-15 catalyst,CH₄ and CO₂ conversion was 98%and 86%respectively,which droped to 85%and 53%after a 120 h reaction.Varied catalystic performances were exhibited over the catalysts after modification by various promoters,and the one modified by 3wt%MgO was the most excellent:Over it,the CH₄ conversion was still about 98%,and the CO₂ conversion dropped to 77%from 92%after a 620 h reaction under the same conditions.For the 10wt%Ni/SBA-15/Al₂O₃/FeCrAl catalyst,the CH₄ and CO₂ conversion was 90.9%and 89.2%respectively, which droped to 36.8%and 25.7%after a 24 h reaction.The modification had a positive effect on the catalystic performance,especially,for the catalyst modified by 7%MgO,whose CH₄ and CO₂ conversion just droped to 94.0% and 75.5%from 98.0%and 80.1%respectively.From the results of characterization,it could be concluded that,the main reasons for the deactivation of the Ni/SBA-15 catalysts were carbon deposition and oxidization of Ni⁰ species during the reaction.And the modification by La₂O₃ or MgO promoter could improve the dispersity of the active component and diminish the formation of the carbon deposition,and the modification by MgO promoter could also enhance the alkalescence of the catalysts.The main reason for the deactivation of the Ni-based metal monolith catalysts was that,most Ni⁰ species converted to NiAl₂O₄ under the function of high temperature and steam.