Co3O4-based catalysts derived from natural wood with hierarchical structure for elemental mercury oxidation

Abstract Wood vessel in natural wood (NW) as the channel for water and inorganic salt transport has a natural aligned microchannel structure and a great hydrophily. In the present work, NW was used as catalyst support which was directly impregnated in Co(NO3)2 solution and then calcined in N2 atmosphere to prepare a catalyst (denoted as Co/NWBC-OS), which was called a one-step calcination method. For comparison, NW biochar (NWBC) derived from pyrolytic NW was also impregnated in Co(NO3)2 solution and calcined in N2 atmosphere to prepare catalyst (denoted as Co/NWBC-TS), which was called a two-step calcination method. Characterization results reveal that NW possesses a greater hydrophily and wettability than NWBC, which is beneficial to impregnation process resulting in a better active components dispersion. In the meanwhile, Co/NWBC-OS has a higher Co3+/Co2+ ratio and more surface chemisorbed oxygen. The higher Co3+/Co2+ ratio can generate more oxygen vacancies which can capture and activate gaseous oxygen to form more surface chemisorbed oxygen. Surface chemisorbed oxygen as the main active site can greatly promote Hg0 removal performance. These results lead to an excellent Hg0 removal efficiency of Co/NWBC-OS which is 99% at 180 °C. Additionally, O2 and NO can promote the Hg0 removal process whereas H2O, SO2 and NH3 exert an obviously prohibited effect on Hg0 removal performance.