Novel,Active And Coke Resistant Pyrochlore-Supported Ni Catalysts For CH₄ Reforming For H₂ Production

With the energy crisis and environmental pollution becoming serious global problems, seeking for novel green energy is one of the pressing issues. Hydrogen, as a clean energy source, offers an alternative to the fossil fuels. C urrently, steam reforming of low hydrocarbons is an effitive way, which has been industrialized for large scale hydrogen production. Among the low hydorcarbons, the abundant storage of natural gas has provided security for its steam reforming for hydrogen production. To improve the hydrogen production effieciency and lower its cost, thus facilitating its application as a green energy, it is nece ssary to develop catalysts with higher activity and more potent resistance to coking. Pyrochlores, which have a chemical formula as A2B2O7, have been found to be active and stable for methane oxidative coupling. In addition, pyrochlores with B sites partly replaced by noble metals have been applied to dry refoming. However, using pyrochlores to support N i as catalysts for reforming for hydrogen production has been rarely investigated. In this study, catalysts with N i supported on pyrochlore supports have been prepared and used for reforming. With the combination of DBD plasma treatment, samples with higher activity, more potent coke resistance and improved stability have been obtained.First, La2Sn2O7 and La2Zr2O7, two pyrochlore compounds with different B s ite cations were prepared and used as supports for N i for methane steam reforming. Compared with Ni/γ-Al2O3, both Ni/La2Zr2O7 and Ni/La2Sn2O7 show very stable reaction performance. While Ni/La2Zr2O7 displays also reasonably high activity for the reaction, the activity of N i/La2Sn2O7 is extremely low. It was found that severe coking occurred to Ni/γ-Al2O3, but no coke formation on the two pyrochlore catalysts. On the reduced and spent N i/La2Sn2O7, Ni3Sn2 and N i3 Sn alloys were detected, which suppress the coke formation but degrade the activity simultaneously. In comparison, a large amount of La2O2CO3 species was formed on the used N i/La2Zr2O7, which can react with the carbon deposits formed on the N i particles to restore the N i sites continuously, thus suppressing the coking effectively and maintaining its initial high activity.Second, a series of N i/La2Zr2O7 pyrochlore catalysts prepared by impregnation method and treated by DBD plasma in different atmospheres and with varied sequences were prepared and applied for dry reforming of methane(DRM). It is found that all of the plasma treated catalysts show evidently improved activity and coke resistance in comparison with the non-plasma treated one. The best performance is achieved on N i/La2Zr2O7-H2P-C, a catalyst treated in H2 plasma before calcination. TGA-DSC and SEM demonstrate that carbon deposition is significantly suppressed on all of the plasma treated samples. Moreover, XRD and TEM results testify that both N iO and N i sizes on the calcined and reduced sa mples treated by plasma are also decreased, which results in higher N i metal dispersion on the reduced and used catalysts and enhances the interactions between N i sites and the support, thus improving the coke resitance and activity of the catalysts.