Ni-based Catalysts Treated By Low Temperature Plasma For Propane Steam Reforming For Hydrogen Production

Hydrogen energy has the feature of clean,safe and high heat value.Its widely application meets the sustainable development concept of the country.As a promising and novel future energy source,it has attracted much attention from the governments and researchers of different countries.Propane steam reforming is one of the important ways for hydrogen production because of the abundance of raw material,highly efficiency for hydrogen production and low reaction temperature.Ni-based catalysts have been used for propane steam reforming by many researchers due to its low cost and high initial activity.However,during the reforming process,easy agglomeration of Ni active sites and coking lead generally the deactivation of the catalysts.By reducing those perovskite and spinel compounds containing Ni cations in their structures,active Ni sites with uniform distribution,small particle sizes and having stronger interaction with the supports can be obtained,thus improving the reaction performance of the resulted catalysts significantly.On the basis of this thought,NiAl₂O₄ spinel and LaNiO₃ perovskite catalysts with bulk Ni species were designed and prepared by the assistance of plasma treating in different atmosphere for propane steam reforming.By using various characterization techniques,the reasons for coking and the structure-reactivity relationship for propane steam reforming have been explored.The major parts of the thesis are summarized:1.NiAl₂O₄ catalysts treated by low temperature plasma in different atmosphere have been prepared and investigated for propane steam reforming.XRD,H₂-TPR and H₂-sorption results have proved that the reduction of NiAl₂O₄-800-H₂p catalyst calcined and treated by plasma in H₂/Ar atmosphere can get metallic Ni active species with reduced crystallite sizes and higher Ni dispersion,which has a stronger interaction with the support.During 50 hours'stability test,NiAl₂O₄-800-H₂p maintains high stability,and its coking amount is less than other catalysts with also a lower degree of graphitization.In addition,O₂-TPD and XPS results show that NiAl₂O₄-800-H₂p possesses a larger amount surface active oxygen species than other catalysts,which is beneficial to remove coking.At the same time, its ability to adsorb C₃H₈ is enhanced,which is beneficial to adsorb and activate C₃H₈ molecules on the catalyst surface.Furthermore,the highly dispersed Ni species can cover the surface acidic sites partly,thus reducing the surface acidity and restricting coke formation on the catalysts.2.LaNiO₃ catalysts treated by low temperature plasma in different atmosphere have been prepared and investigated for propane steam reforming.It is found that LaNiO₃-700-H₂p catalyst treated by plasma in H₂/Ar atmosphere exhibits the highest initial activity and the best stability.No obvious carbon deposit can be detected by TGA-DSC and Raman on the surface of the catalyst after the stability test.In contrast,for the counterpart catalyst without plasma treating,33%carbon deposits can be detected after the stability test. N₂-sorption and XRD results have proved that LaNiO₃-700-H₂p catalyst still possesses mainly perovskite phase,but part of Ni cations in the structure have been reduced into metallic Ni species,and the pore volume and pore diameter of the catalyst have been increased.H₂-TPR and H₂-sorption results display that the Ni species has a stronger interaction with the support,and possesses a higher Ni dispersion and a better active surface area.In addition,O₂-TPD and XPS results show that the plasma treated catalyst forms surface oxygen defects,thus increasing the surface active oxygen amount,which is favorable for removing surface carbon deposits during propane steam reforming.Indeed, these are believe to be the major reason leading to the superior reaction performance of LaNiO₃-700-H₂p for propane steam reforming.