Enhancing the oxidative cleavage of vicinal diols on Fe-ZSM-5 catalysts with hierarchical porosity

Abstract

The oxidative cleavage of biomass-derived vicinal diols holds significant potential for producing valuable renewable carboxylic acids. Fe-ZSM-5 zeolite is a highly effective catalyst for this reaction using mild reaction conditions; however, it suffers from diffusion limitations, particularly with larger substrates. To overcome these challenges, we synthesized hierarchical ZSM-5 zeolite that integrate mesopores within the conventional microporous framework, thereby mitigating diffusion constraints. These hierarchical materials were developed using carbon templating and desilication techniques. Carbon templating led to the creation of well-defined mesopores, while desilication facilitated the formation of hollow crystals. The mesopore-containing hierarchical zeolites led to increased ion-exchange capacity, due to enhanced accessibility of exchange positions for the Fe^3 + cations, with the desilicated zeolite exceeding the Fe-loading by 3.5 times that of the microporous parent ZSM-5 material, as observed by UV–vis spectroscopy, EXAFS analysis and elemental analysis by ICP-OES. Catalytic tests revealed that hierarchical Fe-ZSM-5 catalysts exhibit superior performance compared to their purely microporous counterparts. Specifically, desilication improved catalytic activity for smaller substrates, while carbon templating proved more effective for larger vicinal diols. Furthermore, the carbon templated zeolite displayed enhanced activity per Fe-site, highlighting the benefits of hierarchical porosity in optimizing catalytic performance.