Non-equilibrium electronic structure of Fe-based bulk catalysts: Dual-channel electron transfer behavior among Fe, Zn, and P species and its impact on hydrodesulfurization reaction pathway

Abstract

Regulation of electronic structure of metal active phase for catalysts has been known as efficient in promoting its catalytic activity; however, manipulating the activity of catalysts via controllable metal active phase electronic structure is still challenging. A non-equilibrium electronic structure Fe-based bulk catalyst has been developed via controllably adding P species, where the non-equilibrium electronic structure of Fe species is formed through the electron transfer from the Zn species through the P electronic channel. As a result, the catalytic activity of the modified Fe-based bulk catalysts has increased by 24.4–50.4%. Meanwhile, the sulfurization degree (SD) of the modified Fe-based bulk catalysts has increased by 5.6–25.9%. In addition, the HDS reaction rate constant (kHDS) has increased by about 2.0 times, and the DDS reaction rate constant (kDDS) has increased by about 2.4 times. The P modifying can regulate the directional transfer of unpaired free electrons between Fe and Zn species to form a more non-equilibrium electronic structure of Fe species, which can reduce the energy barrier of the C–S bond adsorbed on the P-modified Fe-based bulk catalysts. Importantly, the P species can be used as an active site to adsorb S-containing compounds in the modified Fe-based bulk catalysts, which is conducive to generating more coordinatively unsaturated sites (CUSs). The former can promote the formation of the more non-equilibrium electronic structure of Fe species, and the latter can adjust the adsorption active site of S-containing on the catalyst surface. Therefore, an electron transfer channel is formed among Fe, Zn, and P species, and another one is formed among Fe, P, and S-containing compounds, which form a dual-channel electron transfer behavior. Furthermore, the specific surface area, total pore volume, and reducibility of the modified Fe-based bulk catalysts have also shown varying degrees of improvement via the controllable addition of P species.