MnOx- and MnOx-CeOx-impregnated SiO2 particles were developed from waste rice husk via a hydrothermal synthesis for removal of Hg0 and NOx. MnOx of 5 or 20 wt% associated with 5 or 10 wt% CeOx was impregnated into resource-recovery mesoporous SiO2. The presence of MnOx and CeOx reduced the specific surface area (SBET) and pore volume of the SiO2 particles. Nevertheless, MnOx(5%)-CeOx(5%)/SiO2 possessed the largest SBET (123 m2 g−1) among the impregnated samples. Electron microscopy images show that the metal-oxide-impregnated SiO2 was plate-shaped with sizes of 3–10 μm. Mn4+/Mn3+ and Ce4+/Ce3+ were the major valence states in the MnOx-CeOx/SiO2 samples; the ratio of Mn4+/Mn3+ increased as CeOx was present. The presence of both amorphous/highly dispersed and crystalline MnOx was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. Removal of Hg0 and NO was achieved by both MnOx/SiO2 and MnOx-CeOx/SiO2 at between 150 and 350 °C. MnOx-CeOx/SiO2 showed greater Hg and low-temperature NO removal potentials than MnOx/SiO2, with MnOx(20%)-CeOx(10%)/SiO2 having Hg0 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 SiO2 adsorbent/catalyst for Hg0 and NOx removal is successful.
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