Comment on “Heterogeneous Catalyst–Microbiome Hybrids for Efficient CO Driven C6 Carboxylic Acid Synthesis via Metabolic Pathway Manipulation”

The effective microbial conversion of syngas into medium chain fatty acids (MCFAs) is limited by factors such as restricted gas–liquid mass transfer efficiency, the toxicity of CO to microorganisms, and energetic constraints. In a recent study by Liu et al. [ ACS Catal. 2022, 12, 5834−5845], a hybrid system was introduced, combining a heterogeneous catalyst and microbiome to enable efficient MCFAs production from CO under mild conditions. The authors extended the chemical synthesis of various compounds, including fuels, light olefins, and oxygenates, which traditionally occur in the gaseous phase at high temperatures and pressures, to this new hybrid system operating in the aqueous phase at 35 °C and with interfering biomass. They claimed that "in the hybrid system, inorganic carbon fixation into organic carbon (adsorbed pyruvic acid) was achieved by the heterogeneous Pt/Fe2O3 catalysts, and the adsorbed pyruvic acid was subsequently metabolized by the anaerobic microbiome." Our perspective raises questions about the conversion of inorganic carbon (CO) into pyruvic acid by the heterogeneous Pt/Fe2O3 catalysts in this hybrid system (operating in the aqueous phase at 35 °C with interfering biomass). We find this claim lacks strong support from existing literature and the experimental evidence provided by the authors. Instead, considering that the biological system alone (without the presence of heterogeneous Pt/Fe2O3) produced MCFAs when supplied with inorganic carbon (CO) and acetate, we propose that the observed enhancement might be attributed to the stimulating effects of heterogeneous Pt/Fe2O3 serving as a biocarrier for the microbiome, rather than the direct chemical synthesis of pyruvic acid.