The design of a novel Pd-nanoparticle-encapsulating covalent organic framework-based catalyst for solvent-free CO2 conversion at ambient pressure

Abstract

The conversion of CO₂ into value-added products offers an economically viable approach to CO₂ capture, contributing to cost reduction in the overall process while aiding in the mitigation of global warming. However, this transformation requires highly effective catalysts due to the thermodynamic and kinetic stability of CO₂. In this study, we explore a new class of covalent organic framework (COF) as a potential catalytic material, leveraging its unique framework chemistry to enhance catalytic efficiency. The considered selection of an olefinic COF featuring a nitrogen-rich core for embedding Pd nanoparticles (Pd-NPs) has led to the enhanced stabilization of the nanoparticles, thereby improving their suitability for long-term catalytic applications. The encapsulation of Pd-NPs on the surface of crystalline COF spheres was thoroughly investigated using XRD, XPS, TEM, and SEM to elucidate the structural integrity and morphology of the resulting catalyst. This novel catalyst exhibits the capability to convert various epoxides into the corresponding cyclic carbonates under ambient pressure and with minimal thermal input. The tailored design of this novel catalytic system led to a maximum 96% conversion with 100% selectivity over multiple cycles without any considerable degradation. The nitrogen-rich core derived from the triazine units plays a crucial role in stabilizing the Pd-NPs, effectively inhibiting Ostwald ripening. The proposed reaction mechanism highlights the significance of Pd-NP encapsulation in the COF spheres for directing selective anti-Markovnikov product formation. Overall, this work demonstrates the potential of nitrogen-rich olefinic COFs, as an alternative to conventional imine-based COFs, to serve as robust platforms for nanoparticle immobilization—enabling the development of efficient catalysts for the sustainable conversion of CO₂ into value-added products.