Hierarchically structured and highly active palladium-loaded Al-MIL-53-linked hybrid periodic mesoporous silica catalysts for Suzuki-Miyaura cross-coupling reaction

Abstract

The rational design and precise preparation of hierarchically structured catalysts (HSCs) with an enhanced catalytic activity and reusability are still enormous challenges in material science and catalysis. Herein, a HSC Pd/Al-MIL-53@HOOC-SBA-15 was successfully prepared by the oriented growth of metal-organic framework Al-MIL-53 into/onto HOOC-SBA-15 via a hydrothermal technique and in-situ deposition of Pd nanoparticles reduced by NaBH4. Such a heterogeneous catalyst was applied to Suzuki-Miyaura cross-coupling reaction (CCR) of various aryl halides and phenylboronic acid. The results showed a highly catalytic performance over 99% conversion/yield, thanks to the crucial role of functional group, the synergistic effect of microporous-mesoporous structure, mesoporous confinement effect and microporous confinement effect. As a comparison, Pd/HOOC-SBA-15 and Pd/SBA-15 were also fabricated for C-C CCR, showing characteristic functional group-protected effect ensuring the stability and redeposition of Pd during catalysis. Based on experimental results, an order on catalytic activity and recyclability is Pd/Al-MIL-53@HOOC-SBA-15 > Pd/HOOC-SBA-15 > Pd/SBA-15 > Pd/Al2O3-C@SBA-15, revealing an excellent catalytic activity and high reusability of Pd/Al-MIL-53@HOOC-SBA-15. Combining with structure and composition of all catalysts, the leaching-redeposition mechanism can well explain highly catalytic performance and deactivation behavior in C-C CCR. This study provides an efficient strategy to prepare large-scale multi-composite HSCs for multi-functionalized catalytic applications.