Construction of electron-rich active sites in the metallic active phase of iron-based hydrogenation catalysts and their regulation on HDN pathway selectivity

• • Cr promotion increases HDN conversion of quinoline by 14.5%–19.7% at 340–380 °C, 4 MPa, and WHSV 8.7 h−1, reaching 81.9% at 380 °C, demonstrating significant activity enhancement for industrial hydrotreating. • • Cr and Zn act as electron donors to sulfided Fe, creating electron-rich Fe sites that weaken Fe–S bonds and promote CUS formation, a mechanistic insight for designing active hydrogenation sites. • • Cr addition increases medium-strength Lewis acid sites, which synergize with CUS to boost hydrogenation activity, highlighting the importance of acid site distribution in HDN catalysts. • • The deep hydrogenation pathway rate constant over FeZn3Cr@GA is 3.2 times that of unmodified FeZn@GA, indicating a shift in HDN pathway selectivity that can improve process efficiency.