Study Of Pd/Fe And Pd-Ce/Fe Magnetical Material For The Removal Of Elemental Mercury From The Coal Derived Fuel Gas

Coal gasification is one of the effective cleaning coal technology.However, Hg is normally released in a gaseous form at high temperatures during the gasification process. The content of Hg0 has been reported to be higher than coal fire procedure with coal gasification procedure being a reducing environment. Besides, mercury is considered as a global threat to human and environmental health because of its toxicity, volatility, persistence and bioaccumulation in the environment. So, it’s quite important to remove heavy toxic metal pollutant effectively and economically in coal gasification procedure. At present, there are three forms of mercury sorbents including activated carbon, noble metal and transition metal oxides. Activated carbon has a poor mercury removal efficiency and regeneration capacity. The noble metal Pd has been considered as the good sorbent for mercury removal at mid-temperature, but it is expensive, mostly being supporting adsorbents. In our preparatory works, a series of sorbents such as γ-Al2O3 and activatedcarbon as supports, the noble metal Pd as active component have been studied and the feasibility of the bimetallic sorbents to remove mercury was preliminary confirmed. But these sorbents can’t be separated and recovered easily for reuse. So in this paper, we report on the development of a facile one-pot method for the direct preparation of nano-magnetite-supported,magnetically recyclable and highly active Pd sorbent and its application in removal of Hg0 in fixed bed. The temperature and H2 S were investigated, the Hg0 removal mechanism over Fe3O4-NH2 and Fe3O4-NH2-Pd sorbents was explored using the results of XRD, FTIR, BET, XPS and TEM. The results indicated that adding Pd can improve the Hg removal performance of the Fe3O4–NH2–Pd sorbent and increase the temperature of capture of Hg0.But easy to be poisoned by H2 S, the regeneration capacity is poor and need to be improved.CeO₂ can react with H₂S quickly in high temperature, so we involve CeO₂ into Pd/Fe3O4 sorbent, prepared PCxF sorbent（P represent Pd, C represent CeO₂,F represent Fe3O4,x is the mass ratio of CeO₂/Fe3O4, from 0.2to 1.5）. As H2 S can be adsorbed by CeO₂ in PCxF, so the introduction of CeO₂ can relieve the poison by H2 S, enhancing Sulfur resistance of sorbent. The conclusions are mainly summarized as follows:（1） The optimum temperature for removal of Hg0 of Fe3O4–NH2 sorbent was 100 °C while Fe3O4–NH2–Pd sorbent was 200 °C. Mercury removal efficiency of both sorbents was reduced with temperature increasing.（2） H₂S was helpful for Hg0 removal of Fe3O4–NH2 sorbent while was inhibited of Fe3O4–NH2–Pd sorbent, the inhibition was remarkable with temperature increasing.（3） The optimum desorption temperature of Fe3O4–NH2–Pd was 300 °C, it can reuse for two times and with good magnetism, which can be separated easily by external magnetic.（4） On the basis of the main products on the surface of the sorbents after Hg0 adsorption, there were two possible mechanisms for the capture of Hg0 over the Fe3O4–NH2–Pd sorbent, by either the formation of HgS or the formation of Pd-Hg amalgam. Based on these results of evaluation experiments and chemical characterization of sorbents, it can be concluded that Pd0 was the main active component.（5） The introduction of CeO₂ can improve the efficiency of Hg0 removal of Pd/Fe3O4 sorbent. When the mass ratio of CeO₂/Fe3O4 was 0.2, the efficiency of Hg0 removal was the best of Pd-CeO₂/Fe3O4 sorbent and can be reached over 85%. It is a prospective candidate for Hg0 control from syngas.H2 and CO was found to be slightly promotional for Hg0 removal.（6） The main active component was also Pd of Pd-CeO₂/Fe3O4 sorbent,the Hg0 capture performance was generally enhanced by the incorporation of Ce as a result of the consumption of H2 S. The individual presence of H2 or CO resulted in the reduction of CeO₂ to CeOn（n<2）.It was the reason that Pd-CeO₂/Fe3O4 had a good regeneration performance。...