Review of CO2 selectivity and its control in the Fischer–Tropsch synthesis of value-added chemicals

Abstract

With the trend shifting from fossil fuels to increasing clean energy demand, studies on Fischer–Tropsch synthesis (FTS) have broadened their directions for synthesizing value-added chemicals, including olefins and oxygenates, on top of producing synthetic fuels. The FTS route provides an efficient way of synthesizing chemicals directly from small molecules (CO and H₂) derived from carbon-containing resources and, more importantly, from biomass and CO₂. The rich olefins synthesized by the FTS provide an alternative to crude oil as feedstocks for further manufacturing high-value chemicals. The study of chemical synthesis by FTS has made remarkable progress in the past decade. Both Fe- and Co-based catalysts have been developed with various promoters and new morphologies and structures. The selectivity toward low-carbon olefins has reached more than 60% with more than 95% olefins in the carbon range of C₂–C₄. However, the emphasis on the high selectivity toward low-carbon olefins has also resulted in high CO₂ selectivity (∼40%), which causes low carbon efficiency and high CO₂ emission. Notably, researchers have paid great attention to controlling CO₂ selectivity with various strategies in the past few years. The discovery and understanding of the active phase, as well as the roles of the promoters in tuning the product selectivity, will be reviewed. The important work and the strategies for controlling CO₂ selectivity will be analyzed and discussed to provide insights for lowering CO₂ selectivity.