Structure-activity Relationship Of MOFs And Their Derived Carbon Materials For The Base-free Removal Of Mercaptans

Mercaptan is one of the active sulfides in light fuels whose transport and consumption are harmful for the production and life of human beings.To replace the polluting desulfurization process using caustic and meet the requirement of environment protection,the development of stable and efficient new catalysts or adsorbents are essential.However,the factors of composition and structure mattering to the desulfurization ability of these catalysts or adsorbents are not understood well,which hinders the development of them.Metal organic frameworks with flexible,clear,adjustable structure and composition are promising materials for the development and investigation of structure-activity relationship of the highly stable and efficient desulfurization material.In this work,the desulfurization ability of MOFs and their derivated carbons were investigated.The base-free catalytic activity of Co/CN-x towards mercaptan was attributed to its CoN structure,the adsorption activity of MOFs was attributed to the types of metal cations and the quantity of coordination unsaturated sites,and the stability and renewability of MOFs was attributed to the coordination environment of the metal cations.Besides,the mechanism of the catalytic or adsorption process of these materials were also revealed.The main contents of this work are as follows:(1)Co/CN-x was prepared by a thermal treatment under H2/Ar atmosphere using Co/ZIF-8 as precursor.This work investigated the influence of composition and pyrolysis temperature of the precursor on the pore structure,construction of basic sites and active sites of Co/CN-x.Besides,the relationship between the composition and structure of Co/CN-x and the catalytic acivity towards the oxidation of mercaptans were also discussed.DFT calculations suggested the deprotonate process of mercaptan was the determining step of its oxidation.And the sulfur atoms bonded to cobalt sites when the hydrogen atoms of thiol group bonded to the pyridine nitrogen at the transition state of the oxidation process,which decreased the energy barrier for the deprotonation of mercaptan.The synergy between pyridine nitrogen and cobalt sites increased the catalytic activity of Co/CN-x towards mercaptan under base-free conditions.(2)A series of CuBDC-x were prepared by a modulator method and treated with a post-synthetic reduction method.The effect of the post-synthetic method was to reduce partial of the Cu2+to Cu+in CuBDC and CuBDC-x.And Cu+ rather than Cu2+was considered to be the active sites for the adsorption of mercaptan by comparing the valence state of copper cations and the sulfur capacity of CuBDC before and after the post-synthetic reduction.Besides,the improved sulfur capacity of CuBDC-x compared with the pristine CuBDC suggested the creating of additional defects was efficient for the improvement of the desulfurization ability of adsorbents.The results of TG,1H NMR,XPS,ICP and EXAFS revealed the role of acetate was to replace BDC2’ linkers.Besides,the quantitative method of defects was also discussed.(3)16 kinds of MOFs consisted of Al,Fe,Co,Ni,Cu,Zn and Zr based SBU and certain linkers were prepared to investigate the composition and structure factors affecting their SADS ability towards mercaptan.Pore structure and specific surface area were considered to mainly affect the mass transfer process of mercaptan.The side group of the ligands had little effect on the SADS of mercaptan and could even hinder the mercaptan molecules to attack the metal cations in SBU.The type of metal cations was supposed to determine the SADS ability of a MOF.With these inferences in mind,four Cu-based MOFs with nearly the same SBU were compared.And combining with the results of XPS,ICP,XRD,leaching tests and recycle tests,the coordination environment of copper cations was demonstrated to determine the binding strength between the copper cations and mercaptans and the stability and renewability of these Cu-based MOFs.