SOx sorption–desorption characteristics by ZrO2-based mixed oxides Original Research Article

SO2 sorption and desorption characteristics of M–Zr oxides (M=Cr, Mn, Fe, Co, Ni, Cu) were studied. Among the M–Zr oxides, Cu–Zr oxide was investigated extensively as a reversible SOx sorbent, which stores and releases SOx in feed gas of oxidizing and reducing atmospheres, respectively. The Cu–Zr oxide showed higher SO2 sorption capacity than CuO or ZrO2 alone. By FT-IR analysis, the bands for CuSO4 were observed on the Cu–Zr oxide after SO2 sorption. The amount of CuSO4 formed during SO2 sorption reaction over the Cu–Zr oxide was more abundant than that over the CuO. Crystallinity of the Cu–Zr oxide characterized by XRD was lower than that of CuO or ZrO2. TPR measurement revealed that the Cu–Zr oxide was reduced at the lower temperature than CuO. In addition, the Cu–Zr oxide was found to exhibit high Cu dispersion and BET surface area, compared to those of CuO or ZrO2. These results indicate that aggregation of CuO or ZrO2 was constrained by mixing the two components, leading to the higher dispersion and surface area.In the cyclic SO2 sorption–desorption operation, a steep drop in SO2 uptake over all the M–Zr oxides except for the Cu–Zr oxide was observed in the beginning of sorption reaction, namely right after the switch from reducing to oxidizing atmosphere. This steep drop disappeared in the case that the sample was treated with O2 before the sorption reaction started, indicating that the steep decrease in the SO2 uptake was brought about by the temperature increase due to re-oxidation of the metals reduced by H2 in the preceding desorption process.