One‐Pot Fabrication of Pd Nanoparticles@Covalent‐Organic‐Framework‐Derived Hollow Polyamine Spheres as a Synergistic Catalyst for Tandem Catalysis

Abstract

Facile fabrication of nanocatalysts consistingo f metal nanoparticles (NPs) anchored on af unctional support is highly desirable, yet remains challenging. Covalentorganic frameworks( COFs) provide an emerging materials platform for structuralc ontrol and functional design.H ere, af acile one-pot in situ reduction approach is demonstrated for the encapsulationo fs mall Pd NPs into the shell of COF-derived hollow polyamine spheres (Pd@H-PPA). In the one-pot synthetic process, the nucleation and growth of Pd NPs in the cavities of the porous shell take place simultaneously with the reduction of imine linkages to secondary amine groups. Pd@H-PPAs hows as ignificantly enhanced catalytic activity and recyclabilityi nt he tandemd ehydrogenation of ammonia borane and selectiveh ydrogenationo fn itroarenes througha na dsorption-activation-reaction mechanism. The strong interactions of the secondary aminel inkage with borane and nitroarenem olecules afford ap ositive synergy to promote the catalytic reaction. Moreover,t he hierarchical structure of Pd@H-PPAa llows the accessibility of active Pd NPs to reactants.

Chemical Conversion and Locking of the Imine Linkage: Enhancing the Functionality of Covalent Organic Frameworks

“…Coupled with other materials, aminelinked COFs were conveniently applied in catalysis and electrocatalysis, with the function of structural scaffolds and adsorption site for the reactant molecules. [53][54] Yaghi and co-workers transformed two layered imine-linked COFs (TPB-TP-COF and 4PE-1P-COF) in the corresponding, isostructural amide-linked COFs by direct oxidation of the C=N in mild conditions (Scheme 4b). [55] The reaction was carried out at room temperature using an excess of sodium chlorite (NaClO2) as oxidizing agent in presence of acetic acid in dioxane for 48 h. The addition of an olefin scavenger such as 2-methyl-2-butene (scavenger of hypochlorous acid generated as a by-product of the reduction of chlorite) further improved the crystallinity of the final material.…”

Integrating single Ni sites into biomimetic networks of covalent organic frameworks for selective photoreduction of CO2

“…[30][31][32][33] Moreover, COFs with tunable porosity can accommodate guest molecules for target applications. [34][35][36][37][38][39] In terms of catalysis, the microenvironment in the cavity of a heteroatom-rich COF may impose complicated effects on the active sites and its catalytic performance. 40 Compared to metalorganic frameworks, organic polymers and inorganic networks, COFs possess a metal-free skeleton and periodic porosity to form biomimetic microenvironments as in plants' leaves for the accommodation of metal molecular catalysts.…”

Chemical Conversion and Locking of the Imine Linkage: Enhancing the Functionality of Covalent Organic Frameworks

“…The improved chemical stability of the modified COF compared to the pristine material was demonstrated by exposing the samples to aqueous solutions at low (6 m HCl) and high (6 m NaOH) pH for 12 h. The amine COFs maintained their crystallinity after the treatments while the unmodified materials partially lost their structure in NaOH and completely dissolved in HCl. Coupled with other materials, amine‐linked COFs were conveniently applied in catalysis and electrocatalysis, with the function of structural scaffolds and adsorption site for the reactant molecules [53, 54] …”