Study On Roles Of Catalysts In Hydrogen Production By Partial Oxidation And Reforming Of DME

Dimethyl Ether （DME） is an ideal hydrogen carrier because of its colorless, non-toxic,non-corrosive property and high hydrogen content （up to13wt%）. Hydrogen production bypartial oxidation and reforming of DME has attracted much attention since the reaction rateand hydrogen producing efficiency are high. Till now, the roles of catalysts in the title reactionhave not been studied well.In this dissertation,0.5wt%Pt/Al₂O₃,12wt%Ni/Al₂O₃,0.2wt%Rh/Al₂O₃and20wt%Co/Al₂O₃catalyst were prepared by impregnation. The reaction process and the catalyst roleswere investigated by examining the impact of catalysts loading manners on H₂yield andproducts selectivity in the decomposition or partial oxidation and reforming of DME in afixed-bed continuous-flow quartz tube reactor. Finally, the performance of Pt/Al₂O₃+Ni/Al₂O₃dual-bed catalysts in the partial oxidation and reforming of DME was investigated.In the DME decomposition reaction, DME decomposed to CH₄, CO and H₂in thegaseous phase when no catalyst was loaded. When the reaction gas was directly introduced onthe catalyst bed, Pt/Al₂O₃catalyst, Ni/Al₂O₃catalyst and Rh/Al₂O₃catalyst can promote thedecomposition of methyl radical to H₂and CO, and inhibit the combination of methyl radicalto produce CH₄and C₂H₆. And the effect of Ni/Al₂O₃catalyst was stronger than the others.When the reaction gas was first introduced into the blank zone, then passed the catalyst bed,the product distribution on the Pt/Al₂O₃catalyst was similar to that of blank reaction, showingthat its main role was promoting the decomposition of free radicals. The disappearance ofC₃H₈product on the Ni/Al₂O₃catalyst indicated that the main role of Ni/Al₂O₃catalyst was toinhibit the combination of free radicals to produce hydrocarbons. Much C₂H₆and C₃H₈produced on Rh/Al₂O₃catalyst showed that Rh/Al₂O₃catalyst can catalyze the synthesis ofhydrocarbon from CO and H₂under reduction atmosphere while promoting the compound ofmethyl radicals. Co/Al₂O₃catalyst deactivated rapidly by carbon deposition in the experiment.In the partial oxidation and reforming of DME, deep oxidation and direct decompositionof DME takes place in the same time. When the reaction gas was directly introduced on thecatalyst bed, Pt/Al₂O₃catalyst, Ni/Al₂O₃catalyst and Rh/Al₂O₃catalyst inhibited the deepoxidation and decomposition of DME. The inhibiting effect of Ni/Al₂O₃catalyst on thedecomposition reaction was a little stronger than that of Pt/Al₂O₃catalyst or Rh/Al₂O₃catalyst, while the inhibiting effect of the latter two catalysts on the deep oxidation was a littlestronger. When the reaction gas was first introduced into the blank zone, then passed thecatalyst bed, Pt/Al₂O₃catalyst, Ni/Al₂O₃catalyst and Rh/Al₂O₃catalyst played the role of reforming of CH₄or DME to CO and H₂, decreasing the selectivity of CH₄. And the effect ofNi/Al₂O₃catalyst was stronger than that of Pt/Al₂O₃catalyst or Rh/Al₂O₃. Co/Al₂O₃catalyststill deactivated rapidly by carbon deposition in the partial oxidation and reforming of DME.The dual bed catalyst with Pt/Al₂O₃and Ni/Al₂O₃catalysts inhibited the decompositionof DME well and promoting the reforming reaction, so as to increase H₂yield and theselectivity of CO.