Abstract
Subnanometer noble metal clusters have attracted much attention because of abundant low-coordinated metal atoms that perform excellent catalytic activity in various catalytic processes. However, the surface free energy of metals increases significantly with decreasing size of the metal clusters, which accelerates the aggregation of small clusters. In this work, new Schiff base–imidazole-functionalized MOFs were successfully synthesized via the postsynthetic modification method. Highly dispersed Pd clusters with an average size of 1.5 nm were constructed on this functional MOFs and behaved excellent catalytic activity in the Suzuki coupling of phenyboronic acid and bromobenzene (yield of biaryl >99%) under mild reaction conditions. Moreover, the catalyst can be reused six times without loss of activity. Such catalytic behavior is found to closely related to the surface functional groups that promote the formation of small Pd0 clusters in the metallic state.
Highlights
Subnanometer noble metal clusters (SNMCs) with dimensions in the range from a few to dozens of angstroms have drawn focused attention (Diez and Ras, 2011; Imaoka et al, 2017; Wang et al, 2020; Yamamoto et al, 2020; Dong et al, 2021)
The preparation of UIO-66–SB–Im and immobilization of Pd0 species to UIO-66–SB–Im are illustrated in Scheme 1
Pd0@UIO-66–SB–Im catalyst was prepared by incorporating the precursor Pd(OAc)2 into the Schiff base–imidazole-functionalized Metal−organic frameworks (MOFs) via coordination and subsequent H2 reduction
Summary
Subnanometer noble metal clusters (SNMCs) with dimensions in the range from a few to dozens of angstroms have drawn focused attention (Diez and Ras, 2011; Imaoka et al, 2017; Wang et al, 2020; Yamamoto et al, 2020; Dong et al, 2021). A solution to the critical issue is to apply a nanoporous supporting material, such as graphene (Gu et al, 2017; Liu et al, 2019), carbon nanofibers (Eid et al, 2019), C3N4 (Yang et al, 2021; Zhang et al, 2021), and porous SiO2 (Peng et al, 2019). Some disadvantages, such as leaching and aggregation of SNMCs, exist during the catalytic process by using these materials as support, which, weaken the catalytic activity (Gu et al, 2017; Liu et al, 2019; Zhang et al, 2021). It is of great importance to design supporting materials that cannot only make ultrafine SNMCs with uniformity and high dispersion and endow the obtained catalysts with excellent catalytic activity
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