Co-ZIF-67 encapsulated phosphomolybdic acid as a hybrid catalyst for deep oxidative desulfurization

Abstract

The introduction of an attractive catalyst for deep oxidative desulfurization (ODS) is a key factor in this process development. The combination of phosphomolybdic acid (HPMo) and a metal organic framework (Co-ZIF 67) in this work provided a new solid catalyst (named HPMo@Co-ZIF-67) for the selective and efficient removal of dibezothiophenes (DBTs) from fuels. A facile in situ strategy called battle around ship (BAS) was utilized to encapsulate HPMo active sites into the synthesized Co-ZIF-67 nanocrystals with a large surface area, stable structure, and defected sites. The prepared bimetallic HPMo@Co-ZIF-67 composite was used for the catalytic oxidative desulfurization (ODS) of bulky DBT from model fuel using TBHP oxidant. The successful incorporation of HPMo into Co-ZIF-67 and the suitable structure of the obtained composite have been verified by different characterization methods, including XRD, SEM, TEM, FT-IR, BET, BJH, and N2 adsorption-desorption. The ultra-deep desulfurization efficiency of 98% was obtained at T = 70 °C once 40 wt% HPMo loading was introduced. The synergetic effects of uniformly dispersed unsaturated Co ions and Mo contributed to the high ODS performance of the catalyst. A kinetic study was also undertaken, and a possible mechanism was suggested. The recyclability experiments were performed using the washing and heat treatment of the used catalyst. Only a 5% loss in the catalyst performance appeared after five consecutive ODS cycles. The catalyst structure also remained unchanged after five cycles, and no substantial HPMo leaching was detected during the ODS treatment.