Effect of surface modification of Fe/g-C3N4 catalyst on the product distribution in CO hydrogenation

Abstract

Carbon nitride (g-C₃N₄) prepared using thermal condensation of urea was pretreated by H₂O₂/NH₃·H₂O and used as support to obtain Fe/g-C₃N₄ catalyst via impregnation method. The catalytic performance of the catalysts both before and after modification was investigated in CO hydrogenation. Combining detailed characterizations, such as XRD, SEM, TEM, FT-IR, TG, CO₂-TPD, CO-TPD, H₂-TPR, contact angle measurement, and N₂ physical adsorption and desorption, we investigated the effects of surface pretreatment on the texture properties of Fe/g-C₃N₄ catalysts and the product distribution of CO hydrogenation. The results demonstrate that various pretreatment techniques have significant influences on the textural properties and catalytic performance of the catalysts. The prepared g-C₃N₄ with a typical honeycomb structure has strong interaction with highly dispersed Fe. Both before and after modification, the materials are hydrophilic, and the hydrophilicity is increased after treatment with H₂O₂ and NH₃·H₂O. Treatment with H₂O₂ enhances surface hydroxyl groups. NH₃·H₂O treatment improves surface amino groups, promotes CO adsorption, and facilitates the formation of Fe(NCN) phase. The surface basicity of all pretreated catalysts is enhanced. The water gas shift (WGS) reaction activity of the two-step modified catalyst Fe/AM-g-C₃N₄ was lower, and the CO₂ selectivity in CO hydrogenation was reduced to 11.61%. Due to the enhanced basicity of Fe/AM-g-C₃N₄, the secondary hydrogenation ability of olefins was inhibited to obtain higher olefin selectivity with C= 2–C= 4 of 32.37% and an O/P value of 3.23.