Study On The Solid Acid And Metal Catalysts Used For DME Steam Reforming To Produce Hydrogen

Nowadays, the remarkably increasing consumption of fossil fuels brings us not only energy crisis but also various environment pollutions. Thus, it is highly necessary to search for clean and sustainable energy sources. As a new clean energy, hydrogen is getting more and more attention from worldwide governments and researchers. In the past several years H2-based fuel cells such as proton exchange membrane fuel cells（PEMFCs） have become research hotspots due to their high efficiency in chemical-to-electric energy conversion. However, as a renewable gaseous energy source, H2 is hard to be stored, compressed and transported, which restrict the wide application of H2-based fuel cells on vehicles. So, the techniques of onboard H2 production from H2-rich carriers must be developed in future. DME steam reforming（DME SR） is now regarded as a promising route for onboard hydrogen production. In this work, we studied the P-modified HZSM-5 solid acid catalysts and the Cu-base spinel MSR catalysts, respectively, and employed them to DME SR reaction.P-modified HZSM-5 catalysts with different P content were prepared. The effects of phosphorus modification on the acidity and catalytic performance of HZSM-5 for DME SR were investigated in detail. Compared with HZSM-5, the P-modified HZSM-5 catalysts（mixed with CuZn AlO catalysts） show not only higher CO₂ selectivity but also higher stability during DME SR. The techniques of N₂ adsorption–desorption, XRD, O₂-TPO, NH₃-TPD, pyridine-IR and 31 P MAS NMR were used for catalyst characterization. NH₃-TPD results show that both the acid quantity and strength of HZSM-5 are changed after P modification. With P content increasing, the density of strong acid sites decreases, while that of weak acid sites changes little. Based upon the results of 31 P MAS NMR, NH₃-TPD and pyridine-IR, a scheme of phosphorus modification on HZSM-5 is proposed.A series of Cu-based spinel catalysts（CuM₂O₄, M=Cr, Mn, Fe, Co, Al） were prepared via citric acid-assisted sol-gel method, the coupling function of Cu-based spinel catalysts and the 5 % P-modified HZSM-5 in DME SR was investigated. Among all spinel catalysts, the CuFe₂O₄ spinel catalyst exhibits the best catalytic performance. The XPS and XAFS results reveal that the CuFe₂O₄ catalyst has the highest Cu⁺/Cu ratio, which is favorable to the formation of HCOO- and COOintermediates during methnol steam reforming. Therefore, the CuFe₂O₄ catalyst exhibits the best catalytic performance and hightest CO₂ selectivity. In addition, the effect of mass ratio of CuFe₂O₄ to 5 % P/HZSM-5 on the DME SR performance of the mixed catalysts was also investigated,it is found that the catalyst with 1:1 mass ratio of CuFe₂O₄ to5 % P/HZSM-5 displays the best DME SR performance at 350 ℃.