Contributions of tailored oxygen vacancies in ZnO/Al2O3 composites to the enhanced ability for H2S removal at room temperature

A series of Ni-doped ZnO/Al2O3 adsorbents with various compositions were fabricated through the sol-gel method. They were then tested dynamically in H2S removal from a gas stream containing H2S in moist N-2. The adsorbents obtained were characterized using Scanning electron microscopy (SEM), transmission electron microscopy (TEM), N-2 adsorption and desorption, Powder X-ray diffraction (XRD), CO2 temperature-programmed desorption (CO2-TPD), UV-Raman spectroscopy, photoluminescence (PL) spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. The dynamic tests for H2S removal showed that the sulfur capacity tended to gradually increase at first and then decrease with the increase in Ni2+ dopant content. XPS, PL and UV-Raman spectra results indicated that the concentrations of oxygen vacancies increased after doping Ni species. The increased breakthrough capacity was strongly related to the concentrations of oxygen vacancies. Oxygen vacancies played a dual role in removing H2S in the dynamic tests. They could efficiently promote H2S dissociation by providing high OH concentrations on the ZnO surface by acid-base interaction. Furthermore, oxygen vacancies could efficiently promote the counterdiffusion of HS- or S2- and O2- in the bulk of ZnO. This mechanism of anion diffusion in the ZnO lattice was supposed in this study.