Modification Of Red Mud And Its Supported Ni Catalysts For Ammonia Decomposition To Hydrogen

Red mud(RM) is a by-product of the Bayer process in alumina industry. It poses a serious pollution hazard due to its high alkalinity and trace radioactivity in case of disposal. And red mud is a valuable secondary resources in terms of it's primarily composition of iron, aluminum, titanium and silicon. The existing open-air damming storage approach not only lead to the waste of land resources and valuable element in red mud, but also cause great harm to the ecological environment and human health. Therefore, the harmless treatment and resource utilization of red mud is the pressing challenges for alumina industry.In view of the strong basicity and structural complexity of bayer red mud, dilute acid digestion and alkali reprecipitation were applied to the red mud sample for modifying the surface and crystal structure, creating the conditions for its catalytic application of high added-value. Then the modified red mud(MRM) was employed as support for preparation of Ni/MRM catalysts by the impregnation method and homogeneous precipitation method, respectively. The textural and structural properties of the as-received red mud(RM), the modified red mud and the as-prepared Ni/MRM catalysts were characterized by X-ray diffraction(XRD), energy dispersive X-ray fluorescence(EDXRF), thermogravimetry-differential scanning calorimetry analysis(TG-DSC), Fourier transform infrared spectra(FT-IR), Scanning electron microscopy(SEM), transmission electron microscopy(TEM) combined with EDX and N2 sorption techniques. And the ammonia decomposition experiments were carried out in a continuous-flow fixed-bed microreactor. The results of catalytic activity measurements showed that these mesoporous nanostructured Ni/MRM catalysts were very active for ammonia decomposition to hydrogen. What's more, compared with impregnation method, using homogeneous precipitation method for loading Ni species can significantly increase the dispersion of Ni element in the surface of modified red mud(MRM) supports, which causes the Ni/MRM catalysts system to obtain the higher catalytic activity under the lower Ni loading.This investigation demonstrates the feasibility of utilizing the waste from the alumina industry for the decomposition of ammonia to hydrogen. Moreover, the use of MRM renders a great promise to be the catalyst and catalyst support for the applications in various catalytic reactions.