(590d) Doped Zno Sorbents for H2S Removal with High Capacity and Wide Temperature Characteristics

Hydrogen sulfide (H₂S) has to be removed to a very low concentration from the gas fuels due to the low sulfur tolerance of the catalysts and precious metal materials in fuel cells (i.e. 0.1 ppmv for PEMFCs and 10 ppmv for SOFCs). Zinc oxide (ZnO) is a widely used sorbent for H₂S removal at moderate temperatures. In this study, nine different transient metal doped ZnO sorbents with a general formula of M_0.05Zn_0.95O were prepared and loaded on SiO₂ particles (100-200 &mum) by pseudo-incipient wetness impregnation. The results of desulfurization tests on these sorbents at room temperature indicate that group IB metal like Ag and Cu doped ZnO/SiO₂ sorbents have higher sulfur capacities than other sorbents. Capacity of Cu_0.05Zn_0.95O/SiO₂ at 0.213 g sulfuer/g ZnO (54% of the theoretical capacity) is twice that of ZnO/SiO₂ sorbent. Test results at 200 °C suggest that Cu_0.05Zn_0.95O/SiO₂ has higher capacity than ZnO/SiO₂ sorbent and there was no carbon oxysulfide (COS) formation in presence of CO/CO₂. In the tests at 400°C, the Cu_0.05Zn_0.95O/SiO₂ demonstrated lower capacity than ZnO/SiO₂ sorbent due to the significant COS formation. As Cu_0.05Zn_0.95O/SiO₂ adsorbed H₂S, the sorbents behaved as a catalyst for the reaction between CO₂ and H₂S, and this reaction kinetics fell into the equilibrium control regime. The comparative study suggests that the copper doped ZnO/SiO₂ sorbents has high heterogeneous contacting efficiency, and no COS formation at low temperatures.