Hydrophobic Modification Of UiO-66 And Its Application In Oxidation Desulfurization Reaction

About 95%of the world’s energy comes from fossil fuels.The Sox produced by the combustion of fossil fuels not only damages the human health,but also causes environmental pollution.All countries have issued a mandatory standard of sulfur content in fuels,which should below 10ppm.As a complementary technology of hydrodesulfurization（HDS）,oxidative desulfurization（ODS）process is considered to be one of the most promising deep desulfurization techniques because of its mild reaction conditions,low cost,and ability to remove polycyclic sulfur compounds which are difficult to be removed by HDS.Metal organic frameworks（MOFs）have unique advantages in catalytic applications due to their ordered porous structure,high specific surface area and easy modification.The previous work showed that during ODS process,the by-product dimethylbenzyl alcohol prefer to occupy the metal active sites,and resulted in the decrease of catalyst activity.Therefore,in this thesis,hydrophobic modification of the catalyst is proposed to improve its stability and activity.the main content includes:Introducing the bifunctional group on UiO-66 by premodification.By introducing-F to tune the surface hydrophobicity of UiO-66,amino group was introduced into the UiO-66structure for the aim of anchoring catalytic active components.With multi-step post-synthetic modification,Schiff-base coordination center were constructed by aldehydes amine condensation to anchor MoO（O₂）₂,thus a series of Mo-based catalysts UiO-66-1/4NH₂-x/4F-sal-MoO（O₂）₂（x=0,1,2,3）were synthesized.MoO（O₂）₂ was also anchored on UiO-66 by direct bonding of amino group with MoO（O₂）₂ to obtain UiO-66-1/4NH₂-1/4F-MoO（O₂）₂.Finally,using phosphomolybdic acid（PMA）as the active center,UiO-66-1/4NH₂-1/4F-PMA catalyst was prepared by cation-anion bonding.The obtained Mo-based catalysts were characterized by means of XRD,SEM,FT-IR,pyridine absorbed IR,ICP-AES,TGA,contact angle test as well as N₂ physical adsorption measurments.The catalytic performance of UiO-66-1/4NH₂-x/4F-sal-MoO（O₂）₂（x=0,1,2,3）for oxidative desulfurization was investigated.With dibenzothiophene（DBT）as model compound,the optimal catalyst UiO-66-1/4NH₂-1/4F-sal-MoO（O₂）₂ and oxidant was selected.The optimal reaction conditions were obtained by orthogonal experiment as follows:catalyst dosage of 0.1g,O/S ratio of 5,reaction temperature of 80^oC.The catalytic efficiency of different sulfur compounds was as follows:4,6-dimethyldibenzo thiophene（4,6-DMDBT）<Benzothiophene（BT）<Dibenzothiophene（DBT）.The kinetic experiments were carried out and the activation energy of the catalytic reaction system was calculated as 100.84 k J/mol.The experimental data and characterization analysis show that the catalytic activity of oxidative desulfurization comes from the synergistic effect between the unsaturated Zr（IV）center on the UiO-66 framework and the supported molybdenum peroxide species.The cycling experiment showed that the fluorine modification significantly improves the cycling stability of the catalyst.Compared with UiO-66-1/4NH₂-1/4F-sal-MoO（O₂）₂,UiO-66-1/4NH₂-1/4F-MoO（O₂）₂obtained by one-step chemical bonding has comparable catalytic activity and cycle stability as that of the multi-step modified catalyst system.It is proved that the one-step chemical bonding method is simple and effective.The cycle stability of UiO-66-1/4NH₂-1/4F-PMA system was poor.XRD and ICP analysis showed that the deactivation of the catalyst was due to the leaching of the active component（PMA）.