Effect on tuning the CO2 hydrogenation to C5+ via co-impregnation: The Role of Cu and K distribution on Fe@TiO₂ catalysts

Abstract

Promoters play a crucial role in optimizing CO₂ hydrogenation by enhancing adsorption and lowering activation energy in heterogeneous catalysts. This study investigates the synergistic effects of potassium and copper on Fe@TiO₂ catalysts, focusing on their structural modification and influence over catalytic performance, mainly C₅₊ production. Characterization results demonstrated that K incorporation significantly increased weak basic sites, highlighting its dominant role as surface modification, enabling rapid CO₂ activation and desorption, preventing surface over-saturation, and facilitating CHx buildup and C–C coupling over Fe and Fe–Cu interfaces. Cu facilitated iron reducibility and CO formation via the RWGS reaction. The co-impregnation method led to a more homogeneous metal distribution, promoting uniform nucleation and minimizing phase segregation during drying and calcination, which improves catalyst stability and accessibility to active sites. Catalytic tests revealed that K10Fe@TiO₂, prepared by co-impregnation, exhibited the best performance with 20 % CO₂ conversion and 47 % selectivity toward C₂⁺ hydrocarbons while minimizing CH₄ formation (≤ 15 %). This preparation method enhanced the promoting effect of Cu in RWGS while optimizing K's role in chain growth via Fischer-Tropsch synthesis. These findings highlight the potential of co-impregnation to fine-tune Fe-based catalysts for selective CO₂ conversion, offering a promising pathway toward sustainable fuel production.