Effect of impregnation sequence of Pd/Ce/γ-AlO sorbents on Hg removal from coal derived fuel gas.

This study attempted to investigate the effect of impregnation sequence of the Pd/Ce/γ-AlO sorbents on Hg removal. To this end, five kinds of sorbents were prepared and tested in simulated coal derived fuel gas (N-H-CO-HS-Hg), including Pd/γ-AlO, Ce/γ-AlO and three kinds of Pd-based sorbents with Ce impregnation on γ-AlO substrate. The tests were conducted at 250 and 300 °C respectively. According to the results, bimetallic Ce-Pd/γ-AlO sorbent prepared by simultaneously impregnating Pd and Ce showed much higher and more stable removal efficiency of Hg than the other three kinds of sorbents. The Hg removal efficiency of Ce-Pd/γ-AlO sorbent reached above 98% within 480 min at 250 °C and 91% within 200 min at 300 °C. Characterization results indicated that the sorbent Ce-Pd/γ-AlO prepared by the co-impregnation method had bigger specific surface area (216.6 m/g) than the other three kinds of Pd-based sorbents. The content Pd and Ce on the sorbent Ce-Pd/γ-AlO surface is 0.21% and 0.61%, which proved higher than that of the other three kinds of Pd-based sorbents, and observation from STEM-XEDS maps showed it demonstrated the highest dispersion. It is found that Ce is likely to promote the dispersion of Pd on the support surface during the preparation of the sorbent under the co-impregnation method. Meanwhile, Ce enhanced the HS resistance of the sorbent. Thereby, Ce-Pd/γ-AlO sorbent is found to have the optimal performance of mercury removal. In this study, the Hg removal mechanism of the Pd/Ce/γ-AlO sorbents in the simulated coal derived fuel gas was also elaborated.