Platform for the Immobilizing of Ultrasmall Pd Clusters for Carbonylation: In Situ Self-Templating Fabrication of ZIF-8 on ZnO

Incorporating metal clusters into the confined cavities of metal-organic frameworks (MOFs) to form MOF-supported catalysts has attracted considerable research interest with regard to carbonylation reactions. Herein, a self-templating method is used to prepare the zinc oxide (ZnO)-supported core-shell catalyst ZnO@Pd/ZIF-8. This facile strategy controls the growth of metal sources on the ZIF-8 shell layer and avoids the metal diffusion or aggregation problems of the conventional synthesis method. The characteristics of the catalysts show that the palladium (Pd) clusters are highly dispersed with an average particle size of approximate to 1.2 nm, making them excellent candidates as a catalyst for carbonylation under mild conditions. The optimal catalyst (1.25-ZnO@Pd/ZIF-8) exhibits excellent activity in synthesizing alpha, beta-alkynyl ketones under 1 atm of carbon monooxide (CO), and the conversion rate of 1, 3-diphenylprop-2-yn-1-one is 3.09 and 3.87 times more than those of Pd/ZIF-8 and Pd2+, respectively, for the first 2 h. Moreover, the 1.25-ZnO@Pd/ZIF-8 is recyclable, showing negligible metal leaching, and, under the conditions used in this investigation, can be reused at least five times without considerable loss in its catalytic efficiency. This protocol can also be applied with other nucleophile reagents to synthesize esters, amides, and acid products. The zinc oxide (ZnO)-supported core-shell catalyst ZnO@MOF, with small apertures on the catalyst surface, provides a potential advantage for isolating metal-atom or metal-clusters sources as guests, which has a positive effect on the stability and activity of the catalyst. These results demonstrate the benefit of using core-shell ZnO@ZIF-8 as a platform for immobilizing ultrasmall Pd clusters for multiple carbonylation reactions.image

Automated summary

The self-templating method is used to prepare the ZnO@Pd/ZIF-8 core-shell catalyst, which shows excellent catalytic performance in carbonylation reactions. The catalyst exhibits high dispersion of Pd clusters and can be reused multiple times without significant loss in catalytic efficiency.