Middle-low-temperature oxidation and adsorption of arsenic from flue gas by Fe-Ce-based composite catalyst

Fe-Ce-based composite catalysts were prepared and used for As₂O₃ catalytic oxidation and adsorption. They were characterized by XRD, BET, H₂-TPR, Raman, SEM and XPS. The results suggests Fe, La and Zr can be partially doped into CeO₂ lattice to form solid solutions. Compared with pure Fe₂O₃, the composite catalysts have stronger low-temperature reducibility, especially La³⁺ doping is beneficial to the formation of more low-temperature active sites. Raman and XPS measurements disclose the presence of oxygen vacancy and surface adsorbed oxygen in composite catalysts and these are more prominent in FeCeLaO. Ce³⁺ ratio increases to 18.30% after reaction, which confirms part of Ce⁴⁺ can participate in As₂O₃ oxidation and be reduced to Ce³⁺. The oxidation and adsorption capacity for As₂O₃ were investigated at different temperatures and O₂ concentrations. The results show FeCeLaO exhibits excellent activity at middle-low-temperatures of 200-400 °C, the oxidation efficiency of As₂O₃ can reach 100%, the total adsorbed arsenic at 400 °C reaches 583.7 μg/g, which is 1.8 times of pure Fe₂O₃ at 600 °C. As₂O₃ oxidation mechanism over FeCeLaO with/without O₂ was proposed through the Mars-Maessen theory with the aid of surface-active oxygen. The abundant oxygen vacancy defects and active chemisorbed oxygen play important roles and guarantee an efficient As₂O₃ oxidation, which is also the essential reason why the composite catalysts can effectively oxidize and adsorb As₂O₃ at middle-low-temperature of 200-400 °C, while pure Fe₂O₃ can only be at high temperature of 600-700 °C.