Performance And Mechanisms Of Molybdenum-based Catalysts For Catalytic Oxidation Removal Of Dibenzothiophene From Oil

With the continuous growth of fuel consumption,people pay more and more attention to the problem of sulfur oxide pollution from fuel combustion.In recent years,countries around the world have issued increasingly stringent regulations and standards for sulfur limits of fuel to solve these pollution problems.Therefore,the efficient removal of organic sulfides in petroleum has become a current research hotspot.Thiophene and its derivatives are sulfur-containing pollutants that are high-content and difficult to remove in oil products.In this study,dibenzothiophene(DBT)from refractory thiophene-containing sulfides was selected as the research object,cyclohexanone peroxide(CYHPO)was used as the oxidant.Catalysts MoO₃-TiO₂@MCM-22 were prepared by the impregnation method using the MCM-22molecular sieve as the support.The structure of the catalysts was characterized,and its performance and mechanism were studied in-deep for the catalytic oxidation removal of DBT.The results showed the prepared catalyst with high-performance for the DBT removal in fuel.The main contents and results were as follows:(1)In this research,novel catalysts of MoO₃-TiO₂@MCM-22 with excellent catalytic performance were successfully prepared via a facile impregnation method.The MoO₃-TiO₂@MCM-22 catalyst with a Mo/Ti mass ratio of 1:4 was marked as MT-1:4,and the other ratio catalysts could be deduced by analogy.Sulfur conversion rates increased in the following order for different Mo/Ti mass ratios on catalytic oxidative desulfurization(ODS):MT-5:0<MT-0:5<MT-1:1<MT-2:3<MT-3:2<MT-4:1<MT-1:4.(2)The as-prepared catalysts were characterized by SEM,HRTEM,N₂adsorption-desorption,XRD,FT-IR,ICP-AES,NH₃-TPD,XPS and Py-FTIR,and the results showed that MoO₃ and TiO₂ were successfully supported on MCM-22.(3)The catalyst MT-1:4 exhibited the highest ODS activity,which reached a sulfur conversion of 99.96%at 373K,catalyst dosage of 0.10 g and O/S molar ratio of2.0 within 15 min.(4)The experimental and characterization results indicated that the enhanced ODS activity was attributed to the synergistic effect between MoO₃ and TiO₂,which was achieved by molybdenum and titanium regulating the concentrations of Lewis and Br?nsted acid sites on the catalyst surface,respectively.Catalyst MT-1:4 achieved the highest concentrations of Lewis and Br?nsted acid sites and the largest combined index,resulting in the highest catalytic activity.(5)The kinetic studies revealed that ODS reaction was a pseudo first-order kinetic process with an apparent activation energy of 48.9 k J/mol.The possible ODS mechanism on MoO₃-TiO₂@MCM-22 included two steps,both of which could be rate-limiting.The former included electron transfer and O-O bond cleavage,and the latter was that the specific O atoms were nucleophilic attacked by the sulfur atoms of DBT.(6)The repeated ODS experiment results displayed that catalyst MT-1:4 was a stable and recyclable catalyst,which could cost-effectively remove DBT from oil products,and thus had superior potential for industrial application.