Characterization of Pd/Al_2O_3 sorbents for elemental mercury capture at high temperatures

摘要

Mercury is considered to be a global threat to human health due to its high toxicity, mobility and persistence in the environment. Coal burning for power generation is the largest anthropogenic sources of mercury emissions in the United States. Recently, gasification has received significant attention as a promising use of coal due to its mitigated effects to the environment. Removal of elemental mercury from syngas is essential for the efficient gas-cleaning system of a coal gasification system for power generation. However, various sorbents, such as activated carbon, are much less effective at high temperatures (>200°C). Palladium sorbent was proved to be an attractive candidate for high temperature Hg removal because it has the highest amalgamation enthalpy. In this work, Pd/Al_2O_3 sorbents with different loading value of Pd was prepared by an impregnation method and employed to remove elemental mercury (Hg~0) at high temperatures. The sorbents were characterized by X-ray diffraction (XRD) measurement and X-ray photoelectron spectroscopy (XPS) analysis. The diffraction line due to PdO became much intensity as the loading value of Pd increased from 1% to 20%. The Pd/Al_2O_3 sorbents with a Pd loading values of 8% exhibited superior Hg~0 removal efficiency at approximately 270°C under pure N_2 condition, which could be ascribed to the better dispersion of Pd. Hg~0 removal efficiency decreased dramatically when temperature further increased to 350°C under pure N_2 condition, which is due to be the occurrence of deamalgamation. The study of such knowledge is very important in developing effective sorbents for the removal of elemental mercury from syngas.