The synthetic evaluation of CuO-MnO x -modified pinecone biochar for simultaneous removal formaldehyde and elemental mercury from simulated flue gas

Abstract

A series of low-cost Cu-Mn-mixed oxides supported on biochar (CuMn/HBC) synthesized by an impregnation method were applied to study the simultaneous removal of formaldehyde (HCHO) and elemental mercury (Hg⁰) at 100–300° C from simulated flue gas. The metal loading value, Cu/Mn molar ratio, flue gas components, reaction mechanism, and interrelationship between HCHO removal and Hg⁰ removal were also investigated. Results suggested that 12%CuMn/HBC showed the highest removal efficiency of HCHO and Hg⁰ at 175° C corresponding to 89%and 83%, respectively. The addition of NO and SO₂ exhibited inhibitive influence on HCHO removal. For the removal of Hg⁰, NO showed slightly positive influence and SO₂ had an inhibitive effect. Meanwhile, O₂ had positive impact on the removal of HCHO and Hg⁰. The samples were characterized by SEM, XRD, BET, XPS, ICP-AES, FTIR, and H₂-TPR. The sample characterization illustrated that CuMn/HBC possessed the high pore volume and specific surface area. The chemisorbed oxygen (O_β) and the lattice oxygen (O_α) which took part in the removal reaction largely existed in CuMn/HBC. What is more, MnO₂ and CuO (or Cu₂O) were highly dispersed on the CuMn/HBC surface. The strong synergistic effect between Cu-Mn mixed oxides was critical to the removal reaction of HCHO and Hg⁰ via the redox equilibrium of Mn⁴⁺ + Cu⁺ ↔ Mn³⁺ + Cu²⁺.