Regenerable Co-ZnO-based nanocomposites for high-temperature syngas desulfurization

H₂S is a common impurity in the syngas derived from municipal solid waste gasification. For power generation using advanced technologies, such as gas engines/turbines or solid oxide fuel cells, reducing the H₂S content to acceptable levels is required. This work investigated the desulfurization performance of bimetallic particles by adding different metals (Fe, Cr, Co, Ni) into ZnO-based nanocomposites. At 400 °C, the Co-ZnO demonstrated 26.3, 5.0, 1.7 times higher sulfur uptake from a model syngas (composed of 100 ppmv H₂S, 15 vol% CO, 5 vol% CO₂, 15 vol% H₂, 15 vol% H₂O and N₂ (balance)) than pure ZnO, Cr-ZnO and Fe-ZnO, respectively. This could be attributed to the formation of p-n heterojunction between the n-type ZnO and p-type Co₃O₄, accelerating surface reaction kinetics. Although the Ni-ZnO showed a better performance at 400 °C, at an elevated temperature of 600 °C, the Co-ZnO demonstrated 1.2 times higher sulfur capacity compared to Ni-ZnO. Furthermore, the Co-ZnO nanocomposite was subjected to 3 cycles of high-temperature desulfurization (600 °C) and regeneration. The results showed that its high desulfurization efficiency was retained after the tests. This could enable a high-temperature desulfurization of hot syngas and hence an increase in the electrical efficiency of waste-to-energy facilities.