Inhibitory effects of water vapor on elemental mercury removal performance over cerium-oxide-modified semi-coke.

A fixed-bed reactor was used to study the effect of water vapor on the efficiency of Hg 0 removal over CeO 2 -modified semi-coke. Adsorption experiments showed that the oxidation activity, and therefore, the mercury adsorption efficiency decreased with increasing water vapor concentrations. Hydrogen temperature-programmed reduction (H 2 -TPR) indicated that the oxidation activity of CeO 2 decreased after water vapor treatment. Fourier-transform infrared (FT-IR) studies revealed that CeO 2 -H 2 O showed new bending vibration peaks at 1110 cm −1 ascribed to Ce–OH groups. X-ray photoelectron spectroscopy (XPS) results showed that the content of Ce–OH increased from 20.85% to 39.99%, while the lattice oxygen content decreased from 68.21% to 45.83% after water vapor treatment. Density functional theory (DFT) calculations revealed that H 2 O can be dissociated on clean and oxygen-defective CeO 2 (1 1 1) surfaces to form H atoms and OH fragments. The H atoms associated with the adjacent oxygen atoms of CeO 2 , and the OH fragments were bound directly with Ce atoms to form Ce–OH for the clean CeO 2 surface; or occupied the oxygen vacancies and were surrounded by three Ce atoms via van der Waals forces, without additional bond formation for the oxygen-defective CeO 2 surface. Thus, the formation of Ce–OH groups and the consumption of lattice oxygens reduced the Hg 0 removal efficiency. [ABSTRACT FROM AUTHOR]