Harnessing the Engineered 2D Triazine-Based Metal-Anchored Covalent–Organic Framework as a Catalyst for Selective Conversion of CO2 into Value-Added Products at Atmospheric Pressure

Recently, covalent–organic frameworks (COFs) have emerged as a new catalytic strategy for the fixation of C1 feedstock of CO2 into heterocyclic compounds, and these compounds can be utilized for production of fine chemicals. In this work, we designed a manganese-anchored COF material (Mn@COF) via a simple, one-pot Schiff base condensation process. The synthesized material of Mn@COF was successfully examined as a promising catalyst for styrene carbonate (SC) synthesis under temperate reaction conditions. The Mn@COF catalyst's inherent properties are well described with the aid of various analytical and spectroscopic techniques, such as Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM), N2-sorption, X-ray photoelectron spectroscopy (XPS), Py-adsorption, and CO2 temperature-programmed desorption (TPD) analysis. The experimental XRD analysis results are in good agreement with the computational structural simulation XRD outcomes and evidently disclose that the Mn metal is successfully anchored to the nitrogen atom in the designed framework based on the observed interlayer and intermolecular distances. These results effectively increase the diffusion of initial reagents and the rate of the reaction in the reaction medium. The bare COF material showed less catalytic activity at atmospheric pressure, but the manganese-anchored COF catalyst (Mn@COF) exhibited superior catalytic activity toward the desired styrene carbonate product under mild reaction conditions. The effect of different reaction parameters in detail is investigated, and additionally, the substrate scope study is examined by using various epoxides under optimized reaction conditions over the Mn@COF catalyst. The promising active sites of triazine N and covalently anchored Mn synergistically enhanced the catalytic activity in the cycloaddition reaction between CO2 and styrene oxide. Interestingly, we proposed a plausible styrene carbonate synthesis mechanism with the assistance of characterization and experimental outputs. Remarkably, with its stable physicochemical and structural properties, the Mn@COF catalyst was recycled for six successive cycles with stable catalytic activity under temperate optimized reaction conditions. This idea emphasizes the selective synthesis of styrene carbonate by CO2 fixation in the presence of a sustainable catalyst under mild reaction conditions.