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

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 H-2) 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 C-2-C-4. However, the emphasis on the high selectivity toward low-carbon olefins has also resulted in high CO2 selectivity (similar to 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.