Fluorine-free strategy for hydroxylated Ti3C2/Ti3AlC2 catalysts with enhanced aerobic oxidative desulfurization and mechanism

Abstract

Hydrofluoric acid is inevitable in most preparation schemes for two-dimensional MXene materials, which is dangerous and environmentally hazardous. Herein, hydroxylated Ti3C2/Ti3AlC2 (h-TC/TAC) catalysts were prepared via an alkaline etching process using a safer, more environmentally friendly alkali. After preferentially forming a hydroxylated Ti3C2 MXene layer on the surface of Ti3AlC2, Ti-C bonds on the surface were partially hydrolyzed, which exposed more active sites. Alkaline etching modulated the chemical composition and electronic structure of the catalyst surface, thus concentrating the active sites on the surface, which improved the activation efficiency and substrate conversion. For the aerobic oxidative desulfurization of a model fuel with a sulfur content of 220 ppm, the prepared catalyst exhibited a desulfurization rate of up to 99% when using air as a cheap molecular oxygen source. The enhanced activity of the h-TC/TAC catalyst was attributed to the continuous activation of molecular oxygen to form •OH and •O2–. Moreover, because the main structure of Ti3AlC2 was maintained, the catalyst could be recycled 8 times without a significant decrease in activity. This work not only shows the potential of alkaline etching for preparing MXene materials but also provides an important example of the thermocatalytic application of MXene and MAX phase materials.