A theoretical investigation on the hydrodesulphurisation mechanism of hydrogenated thiophene over Cu–Mo-modified FAU zeolite

ABSTRACT

We have theoretically investigated the hydrodesulphurisation (HDS) mechanism of hydrogenated thiophene over Cu–Mo-modified FAU zeolite using a two-layer ONIOM (our Own N-layered Integrated molecular Orbital and molecular Mechanics) study. The thiophene is hydrogenated to 2,3-dihydrothiophene (2,3-DHT), 2,5-dihydrothiophene (2,5-DHT) and tetrahydrothiophene (THT) due to moderate free energy barriers. Hydrogenolysis desulphurisation (HYD) and concerted direct desulphurisation (DDS) are discussed. Ring-opening, hydrogen transfer and C−S bond cleavage steps of thiophene derivatives are involved in the HYD process. The rate-determining steps are the hydrogen transfer step for 2,5-DHT and C−S bond cracking step for 2,3-DHT and THT. The concerted DDS pathway is probably more favourable than the HYD pathway in the desulphurisation of 2,5-DHT. The difference charge density (DCD) analysis reveals that for the ring-opening process, the electrons are migrated from the organic chain to the Cu–Mo catalytic centre. The reduced density gradient (RDG) plots indicate that both steric hindrance and a weak van der Waals (VDW) interaction exist between organic fragment and catalytic centre for all transition states (TSs). The localised orbital locator (LOL) maps suggest that there are strong covalent interactions and weak VDW interactions between the atoms in the forming chemical bonds.

KEYWORDS:

• Hydrogenated thiophene
• hydrogenolysis desulphurisation
• ring-opening
• C–S bond cleavage
• hydrogen transfer

5. Supplementary Material

Free energy profiles and relative energies for the formation of sulphur vacancy and HYD pathways of 2,3-DHT and THT, Optimised structures of adsorbed thiophene molecule, TS-2,3DHT-3, and TS-THT-3, Plots of DCDs, RDGs, and LOLs for TS-2,5-DHT-1, TS-2,5-DHT-2, TS-2,3-DHT-2, TS-2,3-DHT-3, TS-THT-2, TS-THT-3 over Cu–Mo–FAU.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was funded by the National Natural Science Foundation of China (Project Number 21203118, 22008155, 22075183, 21878188 and 21975161), IIASA Young Scientists Summer Program (Project Number 21411140044), Science and Technology Commission of Shanghai Municipality Project (Project Number 18090503800), Shuguang Program of Shanghai Education Development Foundation and Shanghai Municipal Education Commission (Project Number 18SG52), Chenguang Program of Shanghai Education Development Foundation and Shanghai Municipal Education Commission (Project Number 19CG69), the Talent Development Foundation of Shanghai (Project Number 2018034), Shanghai Gaofeng & Gaoyuan Project for University Academic Program Development, the Research Fund of Department of Education of Sichuan Province & Gaoyuan Project for University Academic Program Development, the Research Fund of Department of Education of Sichuan Province (No. 18ZB0481), Development of integrated membrane technology for deep treatment of ammonia nitrogen wastewater from rare earth industry (J2018-61), Development of Metal-supported Catalysts for Thiophene Desulfurization (J2019-360), Simulation of Thermal Conductivity of Polymer Matrix Composites (J2020-50-2), Natural Science Foundation of Shanghai (No.19ZR1454900).