In-situ doped Zr, Ce and La promoter on ZIF-67 derived cobalt-based catalysts for syngas to liquid fuels with low CH4 selectivity and high stability

Abstract

ZIF-67-derived cobalt-based catalysts, characterized by high cobalt dispersion and loading, show potential for Fischer-Tropsch synthesis (FTS). However, they typically suffer from low activity and high CH₄ selectivity. This study explores the preparation of Co@C@M catalysts through pyrolysis of doped ZIF-67@M (M = Zr, Ce, and La) precursors, incorporating transition metal and rare earth metal promoters. The catalysts and their precursors were comprehensively analyzed using XRD, N₂ adsorption–desorption, SEM, TEM, ICP-OES, XPS, Raman spectroscopy, TGA, and H₂-TPR. The undoped Co@C catalyst exhibited a cobalt time yield (CTY) of only 1.7 × 10^-5 mol_CO·g_Co^-1·s^-1 and a high CH₄ selectivity of 20 %. In contrast, doping with various promoters significantly influenced catalytic performance, with a volcano-shaped dependence on the type of promoters. Specifically, the Co@C@Zr_x (x = 0.5, 1.0, 2.0, 4.0) series achieved optimal performance at a Zr doping level of 2.0 wt.%. The Co@C@Zr_2.0 catalyst demonstrated a combination of favorable properties, including an optimized pore size, enhanced surface nitrogen content, and lower reduction temperature. These characteristics enabled it to achieve a CTY of 2.8 × 10^-5 mol_CO·g_Co^-1·s^-1, exceptional C₅₊ selectivity (82.0 %), and minimal CH₄ selectivity (7.8 %). Its core–shell structure effectively prevented oxidation of the active cobalt phase, reducing deactivation and maintaining high stability even under conditions with H₂O vapor. This work emphasizes the importance of tailoring active sites and promoter effects to improve FTS catalyst performance, providing valuable insights for the design and development of advanced industrial catalysts.