Regeneration of field-spent activated carbon catalysts for low-temperature selective catalytic reduction of NO_x with NH₃

In the process of producing liquid crystal displays (LCD), the emitted NO_x is removed over an activated carbon catalyst by using selective catalytic reduction (SCR) with NH₃ at low temperature. However, the catalyst rapidly deactivates primarily due to the deposition of boron discharged from the process onto the catalyst. Therefore, this study is aimed at developing an optimal regeneration process to remove boron from field-spent carbon catalysts. The spent carbon catalysts were regenerated by washing with a surfactant followed by drying and calcination. The physicochemical properties before and after the regeneration were investigated by using elemental analysis, TG/DTG (thermogravimetric/differential thermogravimetric) analysis, N₂ adsorption-desorption and NH₃ TPD (temperature programmed desorption). Spent carbon catalysts demonstrated a drastic decrease in DeNO_x activity mainly due to heavy deposition of boron. Boron was accumulated to depths of about 50μm inside the granule surface of the activated carbons, as evidenced by cross-sectional SEM-EDX analysis. However, catalyst activity and surface area were significantly recovered by removing boron in the regeneration process, and the highest NO conversions were obtained after washing with a non-ionic surfactant in H₂O at 70°C, followed by treatment with N₂ at 550°C.