Mechanisms of mercury transformation over α-Fe_2O_3(001) in the presence of HC1 and/or H_2S

摘要

Hematite (alpha-Fe2O3) has been proved to be a promising sorbent for mercury removal in various situations. The mercury removal performance of alpha-Fe2O3 was investigated using a simulated coal gasification syngas containing Hg-0, N-2, HCl, and/or H2S, a series of experiments were designed with HCl and H2S separately and both employed. For a better understanding in the interaction between HCl and H2S in mercury removal, the differences in mercury oxidation were demonstrated on the basis of density functional theory calculations. The rate-limiting step in HgCl2 formation is Hg-0 - HgCl with the energy barrier of 139.47 kJ/mol, but for H2S in mercury oxidation, the generation of active sulfur species is the key step and the rate-limiting step is detachment of second H with an energy barrier of 57.53 kJ/mol. Experimental results point that HCl has inhibition on H2S for mercury removal, it may be ascribed to the competition of active Fe sites on Fe2O3. Conversely, HCl contributes to the mercury oxidation at high temperature while H2S has a limit effect at elevated temperature.