Fabrication and catalytic performance of meso-ZSM-5 zeolite encapsulated ferric oxide nanoparticles for phenol hydroxylation

An encapsulation-structured Fe2O3@meso-ZSM-5 (Fe@MZ5) was fabricated by confining Fe2O3 nanoparticles (ca. 4 nm) within the ordered mesopores of hierarchical ZSM-5 zeolite (meso-ZSM-5), with ferric oleate and amphiphilic organosilane as the iron source and meso-porogen, respectively. For comparison, catalysts with Fe2O3 (ca. 12 nm) encapsulated in intra-crystal holes of meso-ZSM-5 and with MCM-41 or ZSM-5 phase as the shell were also prepared via sequential desilication and recrystallization at different pH values and temperatures. Catalytic phenol hydroxylation performance of the as-prepared catalysts using H2O2 as oxidant was compared. Among the encapsulation-structured catalysts, Fe@MZ5 showed the highest phenol conversion and hydroquinone selectivity, which were enhanced by two times compared to the Fe-oxide impregnated ZSM-5 (Fe/Z5). Moreover, the Fe-leaching amount of Fe@MZ5 was only 3% of that for Fe/Z5. The influence of reaction parameters, reusability, and center dot OH scavenging ability of the catalysts were also investigated. Based on the above results, the structure-performance relationship of these new catalysts was preliminarily described.