Removal of elemental mercury from flue gas using wheat straw chars modified by Mn-Ce mixed oxides with ultrasonic-assisted impregnation

- A novel adsorbent of Mn-Ce mixed oxides modified wheat straw char was prepared.
- Ultrasonic-assisted impregnation method was used to prepare the adsorbent.
- Mercury removal performance and mechanism were studied.
- Presence of CeO2 contributed to the form of Mn/Ce redox cycle.
- Chemical adsorption of Hg0 played a key role in mercury removal.

In this article, Mn-Ce mixed oxides modified wheat straw chars were prepared by an ultrasonic-assisted impregnation method, and were employed to remove elemental mercury (Hg0) from flue gas. Thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) were employed to characterize the physicochemical properties of the catalysts. The effects of ultrasonic-assisted impregnation, Mn/Ce molar ratios, calcination temperatures, Mn-Ce loading values, reaction temperatures and main flue gas components such as SO2, O2, NO and H2O on mercury removal using these catalysts were studied in a fixed bed reactor. The results showed that the catalyst with a Mn/Ce molar ratio of 2/1 exhibited high mercury removal activity at 150 °C. The optimal Mn-Ce loading value and calcination temperature were 0.12 mol/L and 250 °C, respectively. The presence of O2 and NO obviously promoted Hg0 removal. Low concentrations of water vapor and SO2 strengthened Hg0 removal, but high concentrations of water vapor and SO2 inhibited Hg0 removal. Finally, the mercury removal mechanism was also discussed based on experimental results and characterization analysis.