A Theoretical Study On Desulfurization Of Thiophene Over Co-Mo Supported Zeolites

The sulfur component in gasoline can cause SO_xemissions,which will pollute the environment and affect the activity of automobile catalytic converters.Therefore,the removal of sulfur components in gasoline has attracted more and more attention.With the rapid growth of global energy consumption and increasingly stringent environmental regulations,the industry's demand for improving low-quality fuels continues to increase.Traditional desulfurization technologies mainly include fluid catalytic cracking(FCC),hydrodesulfurization(HDS)and adsorption desulfurization,but these technologies have some shortcomings.FCC requires higher operating temperature and economic costs.The HDS process usually needs to be carried out under high pressure H₂conditions,which will lead to a decrease in the octane number.Although adsorption desulfurization avoids the above shortcomings,its low adsorption capacity and material selectivity limit its application.In this paper,the two-layer ONIOM method is used to theoretically study the hydrodesulfurization mechanism of thiophene on transition metal Co-Mo supported zeolite(ZSM-5,FAU,Beta,MCM-22)catalysts.Two ways of thiophene direct desulfurization(DDS)and hydrodesulfurization(HYD)were studied,and the structure and energy of each intermediate and transition state in the reaction were calculated.The results show that in the direct desulfurization mechanism,the reaction rate-determining step is the hydrogen transfer step,in the thiophene direct desulfurization mechanism,the rate-determining step is the cleavage of the thiophene C-S bond;and in the thiophene hydrodesulfurization mechanism,the rate-determines steps are the hydrogen transfer step and the cleavage of the C-S bond.On these four sulfurized Co-Mo zeolites,thiophene is cracked and desulfurized according to the direct desulfurization mechanism,and the activation energy of each transition state is very high,which is difficult to carry out under the experimental conditions;and according to the hydrodesulfurization mechanism,each transition state is generated.The required activation energy is relatively reasonable,and the thiophene desulfurization process on these four zeolites is more likely to proceed according to the hydrodesulfurization reaction mechanism.