Directional Design Of New Adsorbents In Reactive Adsorption Desulfurization And Attempts For Retarding Deactivation

The high speed development of economy in China results in increasing consumption of gasoline,and the air pollution caused by automobile exhausted emissions is becoming more and more serious.Ni/ZnO-based adsorbents is one of the hot research point in reactive adsorption desulfurization?RADS?,where Ni acts as the active component for the hydrogenolysis reaction and ZnO as the sulfur storage component,rendering a good RADS activity and a high sulfur capacity in the Ni/ZnO-based adsorbents.Nevertheless,the commercial adsorbents possess several deficiencies,such as low sulfur capacity and easy deactivation.Therefore,new efficient adsorbents are highly desirable and new methods for retarding the adsorbent deactivation needs to be developed.This dissertation aims at studying the factors affecting the activities of Ni/ZnO-based adsorbents and developing new preparation methods of Ni/ZnO-based adsorbents with high activity and high sulfur capacity.Besides,the mechanism of restarding the formation of spinel,which is the main factor of adsorbents deactivation,was explored.In this way,NiO/ZnO-Al₂O₃ adsorbents with outstanding physiochemical properties was obtained,significantly improving the RADS performance of adsorbents.Nano-structured ZnO was synthesized by homogeneous precipitation self-assembly method using urea as precipitator and P123 as template.The influence of crystallization time on ZnO morphology was investigated and the effect of morphology on the RADS performance was studied.Results showed that small ZnO particles decreased the diffusion resistance of sulfur diffusion in ZnO crystals and promoted the dispersion of Ni.The loose and open architecture of the clew-like ZnO morphology enhances the diffusion of reactants/products in the adsorbent.ZnO-Al₂O₃ composites were prepared via a wet-gel evaporation-induced self-assembly?EISA?method using P123 as template,and Ni/ZnO-Al₂O₃ adsorbents were prepared by incipient impregnation method.The effect of Zn/Al molar ratio on the morphology and desulfurization performance of the adsorbents were investigated.It was found that,the wet-gel EISA method resulted in a good dispersed spherical ZnO on the alumina support,which facilitates the diffusion of reactants/products and the transportation of S from active site Ni to ZnO.The EISA method could provide the adsorbents with high activity and a high ZnO conversion by adding a small amount ofalumina.Titanium was used in the modification of alumina supports.A series of Ti-modified were prepared and compared with unmodified adsorbents to explore the mechanism of retarding the spinel formation by Ti addition.It was found that,Ti existed as TiO2 covering the surface of Al₂O₃,which reduced the interaction between Ni,ZnO and Al₂O₃ and alleviated the formation of spinel phase.As a consequence,the addition of Ti significantly enhanced the RADSregeneration cycle stability of adsorbents and the increased concentration of surface Lewis acid sites by Ti addition is beneficial to the RADS reaction,even though slight decrease of specific surface area and sulfur capacity were observed.Hence,the modification of alumina supports by titanium is effective to retard the deactivation of adsorbents.