Three novel Co(II)-MOFs with a conjugated tetrabenzoic acid supported noble metal nanoparticles for efficient catalytic reduction of 4-nitrophenol

Abstract

The utilization of porous metal-organic frameworks (MOFs) as catalyst support has attracted intensive attentions in heterogeneous catalysis. However, the study of structure-activity relationship in this confined catalysis system is still scarce. Herein, three isostructural Co(II)-MOFs {Co2L(bpy)}n (CTGU-11), {Co2L(bpe)}n (CTGU-12) and {Co2L(bib)}n (CTGU-13) were synthesized by using 4,4′,4″,4‴-(1,3,6,8-Pyrenetetrayl)tetrabenzoic acid (H4L) as an organic ligand, and introducing three N-donor ligands (bpy ​= ​4,4′-dipyridyl, bpe ​= ​1,2-di(4-pyridyl)ethylene, bib ​= ​1,4-bis(1-imidazoly)benzene) with different length. Among these Co(II)-MOFs, each L4− anion bridges four typical paddle wheel secondary building units (SBUs) to form a two dimensional (2D) sheet, which further expanded to the three-fold interpenetrated structure with the aid of different pillared ligands. Inspired by the eligible structure/surface feature of these frameworks, a series of Co-MOF-supported heterogeneous catalysts (NM@Co-MOFs, NM = Ag, Ru, Pd and Au) have been fabricated successfully via solution infiltration, for the reduction of 4-nitrophenol (4NP). Impressively, 2-Ru@Co-MOFs exhibit remarkable activity in comparison to other NM@Co-MOFs composites with the apparent rate constant reach 50.72 ​s-1 ​g-1, 26.14 ​s-1 ​g-1, and 22.79 ​s-1 ​g-1, respectively. Furthermore, the possible catalytic mechanism of 2-Ru@Co-MOFs has also been discussed based on the analysis of reaction kinetics.