Catalytic Plasma Fischer–Tropsch Synthesis Using Hierarchically Connected Porous Co/SiO2 Catalysts Prepared by Microwave-Induced Co-assembly

Abstract

Catalytic plasma-enhanced Fischer–Tropsch synthesis (FTS) for gas-to-liquid conversion was investigated using a recently developed novel nanostructured, hierarchically connected micro/meso-porous Co/SiO2 catalyst obtained through microwave irradiation-induced coassembly of the catalyst and catalyst support precursors ( Catalysts 2020, 10, 152). This catalyst structure with its micron-scale morphological and chemical heterogeneity is particularly suitable for catalytic plasma reactions. It is shown that a dielectric barrier discharge (DBD) can promote FTS over the catalysts at low temperatures and ambient pressure with 100% conversion without any deactivation over a prolonged time scale (175 h in the current study). In contrast to conventional FTS, the hydrogen conversion is higher in plasma FTS, demonstrating that a DBD can promote FTS for more methane and higher hydrocarbon formation. It is shown that the catalyst is not fully reduced and is a mixture of CoO and Co. Carbon deposition present due to incomplete heat treatment of the catalyst to remove the organic coating on SiO2 support results in catalyst deactivation, which can be eliminated by using high catalyst reduction temperature. Furthermore, the catalytic activity increases during the course of reaction due to the plasma-induced morphological changes in the catalyst structure. In the absence of a plasma, catalyst deactivation is very rapid, which is reversed by burning carbon deposit using DBD plasma in oxygen atmosphere at 150 °C. The results indicate that it is possible to develop a new sustainable, distributed FTS technology operating at low temperatures, ambient pressure, and small scale by optimizing the catalyst property, reactor design, and reaction parameters under plasma conditions.