Unveiling the Promoting Effect of Coated Graphite Layer on Iron Catalysts for CO2 Hydrogenation

Abstract Utilizing iron-based catalysts for CO2 hydrogenation reaction represents a promising route for mitigating CO2 levels and producing value-added C2+ chemicals. Yet, the performance is often limited by their complex and sensitive surface structures and reaction microenvironments. In this work, we used a graphite layer with tunable thickness to optimize the surface structure of Fe catalysts and systematically investigated the fundamental role of the graphite layer in Fe-based catalysts, achieving significant improvements in both product value and catalytic stability. The graphite layer modulates the surface microenvironment by optimizing the electronic structure of the active phase. This leads to an increased surface C/H ratio and reduced activation energies for CO2 conversion and light olefin (C2−4=) generation. However, the graphite layer inevitably exerts negative effects on both the carburization of Fe species and the accessibility of active sites. Consequently, the catalytic performance exhibits a volcano-type trend with increasing graphite layer thickness. Compared with pristine Fe catalyst, the optimized Fe@C-6.5 catalyst was found to exhibit 5.2-fold increase in C2−4= selectivity and 1.2-fold increase in C5+ selectivity, with corresponding space time yield (STY) reaching 8.8 and 12.7 mmol·gFe−1·h−1, respectively. Moreover, the graphite layer also has an antioxidation effect on Fe5C2, which significantly improves the stability of the catalyst with no significant deactivation over 110 h of testing. This work not only advances our understanding of the role of graphite layer in surface modification but also provides a practical strategy for developing high-performance CO2 hydrogenation catalysts.