Microwave-assisted carbon-confined iron nanoparticles for steering CO2 hydrogenation to heavy hydrocarbons

Abstract

The key to efficient thermocatalytic conversion of CO₂ lies in the rational design of catalysts. In this work, Fe-based catalysts supported by different carbon materials (AC, GA, CNF, and MPC) were rapidly synthesized with the assistance of microwave heating. Compared with other supports, small-sized active precursors are coated by graphitic carbon layers for GA-supported Fe catalysts, which will slow down the sintering of particles. Small-sized Fe nanoparticles supported by GA present a benign carburization behavior and water removal ability, which play an important role in stabilizing active carbides and improving product selectivity. These features make GA a more promising support material. In addition, for the catalyst obtained by high-temperature calcination, the size of the active precursor is larger than that obtained by microwave heating, and it is easily coated by amorphous carbon shells, whereas for the small active phase precursor obtained by microwave heating treatment, it is encapsulated by graphitic carbons first, and then the amorphous carbon shells gradually appear around the active carbides with the increase in particle size. The carbon-confined environment provides a stable space for steering CO₂ hydrogenation to heavy hydrocarbons. As a result, the rational catalyst exhibits favorable performance. Under relevant industrial conditions (320 °C, 2.0 MPa, 5 g h mol⁻¹), the optimized K–Fe/GA-W-10 catalyst achieves a C₅₊ selectivity of 53.2% at CO₂ conversion of 23.1% and presents a benign stability.