Effect of additive modification on the product distribution in CO hydrogenation catalyzed by Fe/g-C₃N₄

The melamine thermal shrinkage method was used to prepare carbon nitride (g-C₃N₄). Fe/g-C₃N₄ was obtained by impregnation, and Na, K, and Zn additives were added as modifiers. The CO hydrogenation performances of the catalysts were studied before and after modification. The effect of additive modification on the textural properties of the Fe/g-C₃N₄ catalyst and product distribution of CO hydrogenation was investigated by combining several characterization techniques such as N₂ physical adsorption and desorption, XRD, SEM, TEM, FT-IR, TG, CO₂-TPD, Raman, XPS, and contact angle (CA) experiments. The textural characteristics and performance of the catalyst were markedly affected by the additive modifications. Na and K modifications weakened the strong interactions between Fe and g-C₃N₄ and improved the activity of the catalyst; additionally, hydrophilicity was enhanced. The Zn modified catalyst Fe/g-C₃N₄-Zn exhibited a weaker water gas shift reaction activity, and a lower CO₂ selectivity was obtained for CO hydrogenation. In the CO hydrogenation reaction, the Na-modified and K-modified catalysts, which exhibit enhanced surface alkalinity, inhibited secondary olefin hydrogenation and displayed high olefin selectivity and lower CH₄ selectivity. Fe/g-C₃N₄-Na exhibited the highest olefin selectivity, with C₂⁼–C₄⁼ up to 47.5%, and an O/P value of 5.1.