Control of Hg0?and NO from coal-combustion flue gases using MnOx-CeOx/mesoporous SiO2?from waste rice husk.

Abstract MnO x - and MnO x -CeO x -impregnated SiO 2 particles were developed from waste rice husk via a hydrothermal synthesis for removal of Hg 0 and NO x . MnO x of 5 or 20 wt% associated with 5 or 10 wt% CeO x was impregnated into resource-recovery mesoporous SiO 2 . The presence of MnO x and CeO x reduced the specific surface area (S BET ) and pore volume of the SiO 2 particles. Nevertheless, MnO x (5%)-CeO x (5%)/SiO 2 possessed the largest S BET (123 m 2  g −1 ) among the impregnated samples. Electron microscopy images show that the metal-oxide-impregnated SiO 2 was plate-shaped with sizes of 3–10 μm. Mn 4+ /Mn 3+ and Ce 4+ /Ce 3+ were the major valence states in the MnO x -CeO x /SiO 2 samples; the ratio of Mn 4+ /Mn 3+ increased as CeO x was present. The presence of both amorphous/highly dispersed and crystalline MnO x was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. Removal of Hg 0 and NO was achieved by both MnO x /SiO 2 and MnO x -CeO x /SiO 2 at between 150 and 350 °C. MnO x -CeO x /SiO 2 showed greater Hg and low-temperature NO removal potentials than MnO x /SiO 2 , with MnO x (20%)-CeO x (10%)/SiO 2 having Hg 0 removal efficiency of 96% at 150 °C and nearly 100% reduction of NO under a broad operation window of 100–300 °C. These results indicate that resource recovery of waste rice husk for producing SiO 2 adsorbent/catalyst for Hg 0 and NO x removal is successful.