Optimizing Fe-based catalysts for CO2 hydrogenation using combined theoretical predictions and experimental insights

Abstract

Hydrogenation of CO2 to liquid fuel is a crucial technology for e-fuel synthesis in carbon capture, utilization, and storage (CCUS) processes. Designing an efficient catalyst for CO2 direct hydrogenation requires a comprehensive understanding of the active phases and reaction mechanisms. However, the complexity of active phases in Fe-based catalysts and reaction intermediates in CO2 hydrogenation pose challenges in computational approaches. Herein, we identified the active phase of Fe catalysts for CO2 hydrogenation using density functional theory (DFT) calculations. Based on the scaling relations, we constructed descriptor-based micro-kinetic models for CO2-Fischer-Tropsch synthesis (CO2-FTS) and CO-Fischer-Tropsch synthesis (CO-FTS). The derived volcano plot suggested that Fe-Fe3C surfaces are efficient in both the reverse water–gas shift (RWGS) reaction and Fischer-Tropsch synthesis (FTS). Based on the microkinetic model, 16 alloy surfaces were evaluated, suggesting Cu and Mn as promising promoter candidates. The experimental analysis of Fe-Me-K/AC catalysts (Me = W, Zn, Ni, Co, Cu, Mn, B) revealed that carbidic phase composition was mainly governed by the vacancy formation energy of Me-Fe5C2. In catalytic activity tests, Fe-Cu-K/AC catalyst with a high composition of Fe and Fe3C, exhibited the highest C5+ hydrocarbon yield (18.3 %) among the catalysts. This implies that the promoter's effect on the phase composition is more significant than its impact on intrinsic activity. The proposed microkinetic model and promoter screening approach provides insights into catalyst design for CO2 hydrogenation.