Effect of active zinc oxide dispersion on reduced graphite oxide for hydrogen sulflde adsorption at mid-temperature

摘要

Composites of Zinc oxide (ZnO) with reduced graphite oxide (rGO) were synthesized and used as adsorbents for hydrogen sulflde (H_2S) at 300 ℃. Various characterization methods (TGA, XRD, FT-IR, TEM and XPS) were performed in order to link their H_2S adsorption performance to the properties of the adsorbent's surface. Microwave-assisted reduction process of graphite oxide (GO) provided mild reduction environment, allowing oxygen-containing functional groups to remain on the rGO surface. It was confirmed that for the ZnO/rGO synthesize using the microwave-assisted reduction method, the ZnO particle size and the degree of ZnO dispersion remained stable over time at 300 ℃, which was not the case for only the ZnO particles themselves. This stable highly dispersed feature allows for sustained high surface area over time. This was confirmed through breakthrough experiments for H_2S adsorption where it was found that the ZnO/rGO composite showed almost four times higher ZnO utilization efficiency than ZnO itself. The effect of the H_2 and CO_2 on H_2S adsorption was also investigated. The presence of hydrogen in the H_2S stream had a positive effect on the removal of H_2S since it allows a reducing environment for Zn-O and Zn-S bonds, leading to more active sites (Zn~(2+)) to sulfur molecules. On the other hand, the presence of carbon dioxide (CO_2) showed the opposite trend, likely due to the oxidation environment and also due to possible competitive adsorption between H_2S and CO_2.