Liquid-Mediated Si-OH Healing of ZSM-22 Zeolites for Improved Performance in N-Decane Hydroisomerization

The abundant Si-OH groups serving as the defect sites in the ZSM-22 zeolite framework are not only closely associated with physicochemical properties and catalytic performance but are also the primary sites for attack by water molecules, thereby restricting applications involving or producing water. In the present study, a liquid-mediated healing process was used to convert the Si-OH groups in ZSM-22 zeolite into Si-O-Si bonds. The systematic investigation of the treatment solution's composition and the hydrothermal conditions revealed that the crystallinity of ZSM-22 zeolite can be effectively enhanced following optimal healing treatment. Furthermore, the healed ZSM-22 zeolite exhibited enhanced ordering degree and pore connectivity without significant changes to the Si/Al and morphology. Moreover, the decline in Si-OH groups reduced the Lewis acid sites without altering the Brønsted acidity, which led to a slight decrease in the dispersion of Pt particles. In n-decane hydroisomerization, compared to the parent ZSM-22 zeolite catalyst, the healed catalyst demonstrates higher reactant conversion and increased isomer yield, attributing to its enhanced confinement within the micropore voids, which leads to a reduced yield of multi-branched isomers susceptible to cracking. This study presents a potential application of ZSM-22 zeolite in hydroisomerization for complex and challenging feedstocks.