*3.1. Materials*

Manganese chloride (MnCl2·4H2O, purity ≥ 99%, Guangfu Fine Chemical Research Institute, Tianjin, China), 2,5-dihydroxyterephthalic acid (C8O6H6, 98%, DHTP, Heowns Biochem LLC, Tianjin, China), (N, N-Dimethyl formamide (HCON(CH3)2, 99.5%, DMF, Jiangtian Chemical Technology Co., Ltd., Tianjin, China), ethanol (CH3CH2OH, ≥ 99.7%, Jiangtian Chemical Technology Co, Ltd., Tianjin, China), methanol (CH3OH, ≥ 99.7%, Jiangtian Chemical Technology Co., Ltd., Tianjin, China), chloroform (CHCl3, ≥ 99%, Jiangtian Chemical Technology Co., Ltd., Tianjin, China), polyvinylpyrrolidone ((C6H9NO)n, Sigma-Alorich, Shanghai, China), and polyethylene oxide-polypropylene-polyethylene oxide (PEO-PPO-PEP, Sigma-Aldrich, Shanghai, China) were used. The gas mixtures used in this work, including NO/Ar, NH3/Ar, SO2/Ar, and O2/Ar, were supported by Beijing AP BAIF Gases Industry Co., Ltd. All the materials and gas mixtures were used without further processing unless noted.

### *3.2. Catalyst Preparation*

According to the procedure described by Zhou et al. [22], Mn-MOF-74 was synthesized using a hydrothermal method. Briefly, 53 mL of DMF, 3.5 mL of ethanol, and 3.5 mL of H2O were added to a 100 mL beaker and then the ligands DHTP was added into the above mixture. MnCl2·4H2O (0.4396 g, 2.22 mmol) was added into the solution, dispersed by ultrasound for 0.5 h, and then transferred to a Teflon-lined hydrothermal reactor. The hydrothermal reactor was placed in an oven at 135 ◦C for 24 h. The red–brown precipitates produced were cooled to room temperature, centrifuged, and washed three times with 60 mL of methanol. Finally, the product was dried and preserved for use.

The Mn-MOF-74 samples were pretreated for 3 h at a heating rate of 2 ◦C/min in a nitrogen atmosphere at 200 ◦C to remove the residual solvent. P123-Mn-MOF-74 and PVP-Mn-MOF-74 were synthesized by an impregnation method reported in the literature [23]. One gram of P123 or PVP was dissolved in solvent and then 0.2 g of pre-treated Mn-MOF-74 was added into the solution. The mixture was allowed to rest under static conditions at room temperature for 24 h, and then was washed with CHCl3. The initial product was filtered and dried naturally.

Mn-MOF-74-CH3 was synthesized by a post-synthesis modification method referred to in the synthesis method of CH3-MOF-5 [24] but with some modification. Generally, a mixture of 15 mL CHCl3 and 0.2 g pre-treated Mn-MOF-74 was placed in a Teflon-lined hydrothermal reactor and then placed in an oven at 65 ◦C for 12 h. The initial product was washed with CHCl3 three times to remove unreacted species. The solids were dried at room temperature and stored in a desiccator for use.
