Activities Of The Rare-Earth Perovskite Catalysts In Supercritical Water Gasification Of Syngas For Corn Stalks

Biomass gasification in supercritical water is a highly efficient, clean energy conversion and utilization technology, which was developed in recent years. In this paper, the rare-earth perovskite-type catalysts LaNixFe1-xO3(x=0.1,0.3,0.7,0.9)were prepared by the citric acid method, and one of the better activity catalyst compared with the corresponding perovskite-type catalysts LaFeO3, LaNiO3and La2NiFe06. And different reaction temperature on supercritical water gasification (SCWG) for corn stalks of syngas was studied. The catalysts were characterized by X-ray powder diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), specific surface area (BET), scanning electron microscopy (SEM), magnetic property and Mossbauer spectroscopy, and was tested for SCWG of corn stalks. In addition the industrial composition of corn stalks also tested by the TGA analysis.Results showed that a single-phase rare-earth perovskite oxide LaNixFe1-xO3(x=0.1,0.3,0.7,0.9), LaFeO3, LaNiO3and La2NiFe06 could be formed by sol-gel method. The LaNi0.3Fe0.7O3 demonstrates the best catalytic activity for SCWG of corn stalks in the series of catalysts LaNixFe1-xO3. It shows maximum hydrogen content in the product, and best gas conversion and gasification rate, which could be related to a lower reduction temperature, large specific surface area and morphology of lamellar structure.Meanwhile, the rare-earth double perovskite-type catalyst La2NiFeO6, with the corresponding single perovskite-type catalysts LaFeO3, LaNiO3 and LaNi0.3Fe0.7O3 were systematically compared. The results showed that the double perovskite catalysts have good conversion and gasification rate than others. This is because La2NiFe06 catalyst exist a smaller particle size and lattice distortion. Mossbauer studies demonstrate the majority of iron in the perovskite is Fe3+-ions, and single perovskite-type catalyst contain two coordinated Fe3+-ions except single-phase perovskite LaFeO3, while the double perovskite containing only Fe3+-ions in octahedral coordination, ascribe to the good crystalline phase of LaFeO3.Furthermore, the influence of different reaction temperature in SCWG of syngas was discussed. The products were analyzed by gas chromatography, infrared spectroscopy (FT-IR), elemental analysis and GC-MS. And the reaction mechanism of the process was discussed according to GC-MS analysis. The results showed that the critical temperature influence the volume fraction of gas products, with increase of temperature, gasification rate of hydrogen and carbon will be increased, and a maximum value at 500℃. Liquid products mainly included phenols, five-membered ring ketone and straight-chain alkanes. Carbohydrate formed by the hydrolysis of corn stalk with high temperature and pressure conditions at first, then the redox reaction of open-loop, dehydration, isomerization occurred.