Encapsulating UiO-66-NH2@Pt with defective PCN-222 as an active armor to fabricate a sandwich-type nanocatalyst for the tandem synthesis via hydrogenation of nitroarenes
The heterogeneously tandem catalytic synthesis is a step-economic and work-up-saving strategy for producing chemicals, but it usually requires a special catalyst to achieve the sequential catalytic reactions . The development of metal organic frameworks provides an opportunity to fabricate multifunctional catalysts. In this work, a MOF-based sandwich-nanostructure catalyst UiO-66-NH 2 @Pt@PCN-222 is fabricated, which is made of the UiO-66-NH 2 as the core, Pt nanoparticles as the interlayer, and the defective PCN-222 as the shell. The developed catalyst shows outstanding performance for the tandem catalytic synthesis, which is the hydrogenation of nitroarenes cascaded with β-dicarbonyl compounds to form β-ketoenamines. The selectivity of β-ketoenamines reached 98% upon the completed hydrogenation of p-nitrotoluene. The stable PCN-222 shell can be regarded as an active armor, which not only protects the Pt particles from leaching or agglomerating, but also has plenty of acid sites that are conducive to the second-step condensation. At the same time, the kinetic studies show that the armor layer also affects the activity of hydrogenation, so that the hydrogenation and condensation reactions can proceed simultaneously to give the best selectivity. Various substituted dicarbonyl compounds and structurally different nitroarenes completed the conversion with excellent conversion (90–99%) and selectivity (87–98%), and this nanocatalyst can be recycled for up to six cycles without the expense of activity.
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