Preparation Of Transition Metal Composite Catalysts And Their Oxidative Desulfurization Performance On Diesel

Organosulfur compounds in fuel oil will produce massive SO_xduring combustion,causing serious environmental pollution.At present,as a main industrial desulfurization method,hydrodesulfurization is difficult to efficiently remove dibenzothiophenes（DBTs）sulfides from diesel.From the view point of redox reaction,the more difficult the sulfide to be reduced by hydrogenation,the easier by oxidation,thus,the oxidative desulfurization（ODS）process is highly expected.Furthermore,with milder reaction conditions,ODS process is more in line with the development of green chemical industry.Thus,a series of transition metal composite catalysts were designed and prepared,and their ODS performance was studied.First,the ODS process based on ionic liquids phase transfer catalysts[C₁₆MIM][PMo O]and Na Cl O was developed without using extractant,and the oxidation mechanism of Na Cl O was investigated.The lipophilicity of the catalysts guarantees their phase transfer property,and their catalysis follows the order[C₁₆MIM][PMo O]>[C₁₆MPy][PMo O]>[C₁₆TMA][PMo O]>[C₄MIM][PMo O]>[C₂MIM][PMo O].After 8 recycles,[C₁₆MIM][PMo O]can still achieve a complete oxidation of DBT in model or real diesel within30 minutes.Under the catalytic action,Na Cl O is decomposed to·O₂^-and·OH,whereby the Mo=O of the active center is oxidized to the peroxy Mo-O-O,and DBT is in situ oxidized to DBTO₂.A novel ODS catalytic system was developed for oil-water two-phase reaction,which is conducive for the development of ODS technology.Meanwhile,the free radical oxidation mechanism of Na Cl O in the ODS process was elucidated for the first time.Second,the ODS process using poly（ionic liquids）（PILs）nanocore-shell catalyst Si O₂@V-PIL and cumene hydroperoxide（CHP）was studied.The nanocore-shell structure achieves uniform distribution and full exposure of active centers,and greatly improves the ODS catalytic performance.Compared with amorphous catalyst V-PIL and supported catalyst V-PIL/Si O₂,Si O₂@V-PIL has a higher catalytic activity that can oxidize all the DBT within 1 h under mild reaction conditions.And,99.9%desulfurization rate can be retained after 5 recycled uses of the catalyst.This ODS process further promotes the industrial application prospective of oil-soluble oxidants.And preparation of nanocore-shell catalyst Si O₂@V-PIL provides a method for the structural optimization of PILs catalysts.Third,the ODS process based on core-shell bifunctional nanosized catalyst Cu O/Si O₂@V-PIL and O₂was developed,and the unique in-situ radical initiation of which enhanced the ODS reaction rate by O₂.The in-situ radical initiation can shorten the start-up time of ODS from 90 min to 40min,and achieves 99.9%desulfurization,91.5%cumene conversion,and82.8%CHP selectivity within 1.5 h.On the core-shell interface,the peroxy bond V（O）₂is decomposed to oxygen radicals,which is used directly by Cu O for in-situ radical initiation.Then,Cu O catalyzes the oxidation reaction of cumene by oxygen to CHP,and CHP realizes the ODS of diesel under the catalysis of V-PIL.Furthermore,other alkylbenzene compounds（like toluene,ethylbenzene and diethylbenzene）in diesel can be also oxidized to organic peroxides,suggesting a high universality of this ODS process.The in-situ radical initiated indirect ODS process by oxygen is highly innovative,and its mechanism has reference significance for oxidation of other organic compounds.Fourth,the steric hindrance of alkyl DBTs has been identified as the controlling factor in ODS process of real diesel for the first time.Alkyl DBTs（C₂-DBT,C₂-C₂-DBT,C₃-DBT,and C₃-C₃-DBT）with different steric hindrances were synthesized,and their ODS difficulty was studied in homogeneous（HPW+H₂O₂+HAc）and heterogeneous systems([C₁₆MIM][PWO]+H₂O₂,V-PIL+CHP,and[C₁₆MIM][PMo O]+Na Cl O).The results show that in homogeneous catalysis,the oxidation of alkyl-DBTs is hardly affected by the steric effects,while in heterogeneous catalysis,their oxidation is highly dependent on the steric hindrance,following the order of C₃-C₃-DBT>C₃-DBT>C₂-C₂-DBT>C₂-DBT>DBT.The steric hindrance arises from the shielding effect of the electron clouds of alkyl-DBTs on S atom,which hinders its accessibility to the active sites of the solid catalyst.The longer alkyl substituted chain,the greater the steric hindrance,and thus,high-carbon alkyl DBTs in real diesel are difficult to remove.In a short,eliminating steric hindrance is the key for the efficient ODS of real diesel,and this view is instructive for the design of catalyst and improvement of ODS process.Finally,the ODS process using sea urchin-like VO_x nanocatalysts and CHP is developed,which eliminates the steric hindrance of alkyl DBTs through pseudo-homogeneous catalysis,and realizes deep desulfurization of real diesel.Compared to nanosheet VO_x,nanoblock VO_x-1-700 and VO_x-2-700,micron bulk VO_x-1-500 and micron V₂O₅catalysts,the sea urchin-like VO_xnanocatalyst can achieve deep ODS of real diesel within 1.5h.The 1-3 nm“needle tip”of the sea urchin-like forms a pseudo-homogeneous catalysis,which combines the advantages of homogeneous and heterogeneous catalysts,and effectively eliminates the negative effect of steric hindrance of alkyl DBTs.Sea urchin-like VO_xis a novel nanocatalyst with potential industrial application in deep desulfurization of real diesel,and sheds a light for the rational design of ODS catalysts.