A multifunctional hierarchical metal-organic aerogel monolithic catalyst with secondary hollow-structure for the...

The elaborately crafted microstructure and the accommodated active species of catalyst hold great significance for improving catalytic performance. The synthesis of hierarchical multifunctional catalysts through the integration of two or more distinct active sites in porous supports (e.g., metal-organic frameworks (MOFs)) have provided promising schemes for designing sophisticated catalytic systems, especially in the tandem synthesis of complex molecules. However, the construction of such multifunctional catalytic systems is complicated. Additionally, their powder state of these catalysts inevitably exhibits poor machinability and recyclability. More importantly, the design of classical monolithic catalysts faces the challenge of constructing exquisite secondary micro-nanostructures that favor mass transfer and catalytic kinetic processes. Herein, we fabricate a composite monolithic agarose (AG) aerogel catalyst Pd@H-UiO-66-NH₂/AG (H denotes the hollow structure) equipped with secondary hollow-structured amino-functionalized hafnium (Hf)-based MOF nanoreactors (Pd@H-UiO-66-NH₂), which precisely encapsulates palladium nanoparticles (Pd NPs). Benefiting from the enhanced kinetic process afforded by the well-crafted secondary hollow structure and the integration of Pd NPs, MOF-positioned Lewis acid sites (Hf⁴⁺) and amino groups within the monolithic catalyst, Pd@H-UiO-66-NH₂/AG exhibits high catalytic performance in the synthesis of benzylidene malononitrile (BM) from benzyl alcohol (BA) and malononitrile, achieving a 95.2 % yield. Furthermore, the composite monolithic catalyst can be effortlessly recovered for at least five times without a significant loss of activity. The monolithic catalysts fabricated by equipping multifunctional nanoreactors herein provide distinctive insights for the development of practical application-oriented monolithic catalysts for tandem synthesis.