Critical Role Of Water In The Removal Of H₂S By ZnO And Construction Of Carbon-doped ZnO Adsorbent

Zinc oxide?ZnO?,due to its favorable thermodynamics of the sulfudization,is widely used as a dry desulfurization sorbent to remove hydrogen sulfide?H₂S?comparing with other metal oxides.Although ZnO has higher desulfurization efficiency indicated by thermodynamic studies,the desulfurization property of ZnO is quite poor under dry conditions at room temperature limited by kinetic factors.Previous studies confirm that ZnO is of better desulfurization activity in the presence of water vapor,that is,water could significantly improve the desulfurization performance of ZnO at room temperature.However,there is no specific and unified illustration for the influence of water on H₂S removal by ZnO in the existing research results.Understanding of the critical role of water in the desulfurization process is meaningful for preparing new sorbents with better performance and guiding the desulfurization process in practical industry operation.In this work,we firstly identify that water adsorbs on the surface of ZnO in the forms of hydroxyl group,chemisorbed water molecule and physisorbed water molecule through in situ diffuse reflectance infrared Fourier transform?DRIFT?and X-ray photoelectron spectroscopy,and then perform an experimental and computational study to illustrate their corresponding role during H₂S removal by ZnO;subsequently we modify ZnO with the purpose of improving the hydroxylation level of ZnO surface.The main innovative results are listed as follows:1.Through the experimental and computational study,we provide a fresh framework for interpreting the role of water in H₂S removal at room temperature.Water adsorbs on the surface of ZnO in the forms of hydroxyl group and chemisorbed and physisorbed water molecule.The hydroxyl group on the surface of ZnO changes the elementary steps of desulfurization process,leading to a significant decrease of the energy barrier.Accordingly,the reaction rate increases and the activity of ZnO improves.The chemisorbed water molecules can dissociate to form new hydroxyl groups and thus sustain the activity of ZnO.Moreover,the physisorbed water molecule acts to inhibit the elementary step of S changing adsorption mode in the path initiated by the hydroxyl group,leading to a bad performance of desulphurizer.2.A kind of carbon-doped ZnO is prepared via glucose co-impregenation.On the one hand,the formation of C-O-Zn bond could improve the amount of hydroxyl group on the surface of ZnO sorbent and thus increase the activity of ZnO.On the other hand,the introduction of glucose significantly increases the dispersion of ZnO and reduces the particle size of ZnO,increasing the number of active site.Furthermore,the activation energy and the length of the reaction path between carbon-doped ZnO and H₂S are reduced.The combined action of those three factors mentioned above improves the desulfurization performance of zinc oxide at room temperature.