Eco-friendly solid-state synthesis of Na-promoted Mn-Fe/ZrO2 catalyst for Fischer-Tropsch synthesis

Abstract

The advancement of large-scale and environmentally-friendly solid-state synthesis methods is of paramount importance for the production of precipitated catalysts, notably Fe-based catalysts utilized in Fischer-Tropsch synthesis (FTS). In this study, we present an innovative solvent-independent, wastewater-free solid-state approach for the synthesis of highly efficient Fe/ZrO2 catalysts, elucidating the mechanisms of promotion within this specific methodology. The prepared catalysts underwent rigorous evaluation under industrially-relevant FTS conditions (230–270 °C, 20 bar, and WHSV = 5400 mL/(gcat⋅h)). A comprehensive suite of characterization techniques was employed to establish the intricate interplay between catalytic activity and structural attributes. We meticulously examined the impact of Na as an alkali promoter and the role of transition metals (Cu and Mn) in enhancing FTS catalytic performance. The catalytic outcomes obtained clearly demonstrate the pivotal role of the synergistic interaction between Mn and Na within the Na-Mn-Fe/ZrO2 catalyst system in driving the FTS reaction. This synergism significantly enhances FTS performance, yielding an impressive CO conversion rate (89.91 %) while maintaining low selectivity to CH4 (7.75 %). The incorporation of Mn and Na into the catalyst matrix enhances the dispersion of Fe2O3, thereby improving the reducibility of Mn/Fe oxides and elevating the electron density on the catalyst surface. These factors facilitate the formation of active Hägg iron carbide (χ-Fe5C2), stimulating chain propagation and ultimately leading to the generation of valuable C5+ hydrocarbon products, which underscores its potential as an optimal candidate for future industrial applications in Fe-based Fischer-Tropsch synthesis.