Effect of MgO promoter on Ni-based SBA-15 catalysts for combined steam and carbon dioxide reforming of methane

摘要

A series of Ni/SBA-15 catalysts with Ni contents ranging from 5 wt%to 15 wt%.as well as another series of 10%Ni/MgO/SBA-15 catalysts.in which the range of the MgO content was from 1 wt%to 7 wt%,were prepared,and their catalytic performances for the reaction of combined steam and carbon dioxide reforming of methane were investigated in a continuous flow microreactor.The structures of the catalysts were characterized using the XRD,H2-TPR and CO2-TPDtechniques.The results indicated that the CO selectivity for this reaction was very close to 100%.and the H2/CO ratio of the product gas could be controlled by changing the H2O/CO2 molar ratio of the feed gas.The simultaneous and plentiful existing of steam and CO2 had a significant influence on the catalytic performance of the 10%Ni/SBA-15 catalyst without modification.After reacting at 850℃ for 120 h over this catalyst.the CH4 conversion dropped from 98%to 85%.and the CO2 conversion decreased from 86%to 53%.However,the 10%Ni/3%MgO/SBA-15 catalyst exhibited a much better catalytic performance,and alter reacting for 620 h,the CO2 conversion over this catalyst dropped from 92%to around 77%,while the CHd conversion was not decreased.Oxidation of the Ni0 species as well as carbon deposition during the reaction were the main reasons for the deactivation of the catalyst without modification.On the other hand,modification by the MgO promoter improved the dispersion of the Ni0 species.and enhanced the CO2 adsorption affinity which in turn depressed the occurring of carbon deposition,and thus retarded the deactivation process.