Adsorption Performance of Cu-Fe Bimetallic-Modified Coconut Shell Activated Carbon for Ultra-Low-Concentration SO2

In this study, Cu-Fe bimetallic-supported adsorbents were prepared using alkali-activated coconut shell activated carbon (AC-OH) as a carrier by impregnation method. To optimize the adsorption effect, the effects of the second metal type, Fe loading amount, Cu/Fe ratio, and operating conditions on the adsorption effect of extremely low-concentration SO2 (1 ppm) were systematically investigated. The results showed that when the Cu loading was 5% by mass and the Fe loading was 3% by mass, the adsorbent exhibited optimal adsorption performance, with a breakthrough time of up to 36.5 h and a corresponding breakthrough sulfur capacity of 14.424 mg/g. Further exploration of the conditions shows that the coexistence of O2 and H2O can significantly promote the adsorption of SO2, while reducing the space velocity is beneficial for prolonging the breakthrough time. In terms of regeneration stability, after two adsorption–regeneration cycles, the adsorption activity of the adsorbent decreased to 72.7% of the fresh sample, and the deactivation was mainly attributed to the accumulation of sulfate species and the loss or aggregation of active components. By combining XRD, FT-IR, XPS, SEM and other characterization techniques, the structure–activity relationship and deactivation mechanism of the adsorbent were analyzed. This bimetallic-modified activated carbon has shown great potential for deep purification of extremely low concentrations of SO2.