Direct oxidative carboxylation of olefins catalyzed by iron-based polyoxometalate metal organic frameworks

Abstract

The conversion of carbon dioxide (CO2), into value-added products such as cyclic carbonates is of academic and industrial interest. The cyclic carbonates have various industrial applications although they are usually produced from epoxides using environmentally unfriendly processes. This study presents a green approach for production of cyclic carbonates from readily available olefins catalyzed by iron-based polyoxometalate metal organic framework (FePOM@MOF). The FePOM@MOF catalyst was characterized using different techniques such as Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), Zetasizer, powder X-ray diffraction (PXRD), Transmission electron microscope (TEM) and Inductively coupled plasma-mass spectroscopy (ICP-MS). The catalysed oxidative carboxylation process was carried out in a stainless-steel autoclave reactor and the products were analysed using GC-MS and GC-FID against biphenyl as the internal standard. The optimal reaction conditions were determined using response surface methodology with styrene as the model substrate and hydrogen peroxide as the oxidant. Under optimal condition of catalyst load (0.075 g), reaction time (7 hours), CO2 pressure (20 bars), and reaction temperature (60 ℃), the process achieved a styrene conversion of 78.1%, styrene carbonate selectivity of 64.2% and yield of 50.1%. When the FePOM@MOF catalyst was tested on styrene derivatives such methylstyrene and chlorostyrene, the catalytic system produced the desired cyclic carbonates in 50.7% and 43.9% yield respectively. On the other hand, when that catalyst was tested on 1-hexene and cyclohexene olefin substrates, the cyclic carbonate yields produced were 18.5% and 16.5% respectively and these were inferior compared to the results obtained with styrene and its derivatives. The catalytic system was also found recoverable at the end of the reaction and reused without significant loss in catalytic reactivity.