Mechanisms of mercury transformation over α-Fe2O3(0 0 1) in the presence of HCl and/or H2S

Hematite (α-Fe 2 O 3 ) has been proved to be a promising sorbent for mercury removal in various situations. The mercury removal performance of α-Fe 2 O 3 was investigated using a simulated coal gasification syngas containing Hg 0 , N 2 , HCl, and/or H 2 S, a series of experiments were designed with HCl and H 2 S separately and both employed. For a better understanding in the interaction between HCl and H 2 S in mercury removal, the differences in mercury oxidation were demonstrated on the basis of density functional theory calculations. The rate-limiting step in HgCl 2 formation is Hg 0  → HgCl with the energy barrier of 139.47 kJ/mol, but for H 2 S 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 H 2 S for mercury removal, it may be ascribed to the competition of active Fe sites on Fe 2 O 3 . Conversely, HCl contributes to the mercury oxidation at high temperature while H 2 S has a limit effect at elevated temperature.