Unveiling the roles of Fe-Co interactions over ternary spinel-type ZnCoxFe2-xO4 catalysts for highly efficient CO2 hydrogenation to produce light olefins

Abstract

Currently, the CO2 conversion to light olefins is attractive in clean energy research. Despite numerous works on Co-Fe bimetallic catalysts, the lack of well-defined bulk structures with identical crystalline phase and similar textural property hinders the in-depth understanding of the roles of Fe and Co species. Herein, series of uniform K-containing spinel-type ZnCoxFe2-xO4 nanoparticles (x = 0, 0.5, 1.0, 1.5, 2.0) were successfully synthesized via a single source layered double hydroxide precursor route. Compared to ZnFe2O4 and ZnCo2O4, as-fabricated ternary ZnCo0.5Fe1.5O4 spinel nanoparticles as the catalyst exhibited an outstanding performance toward CO2 hydrogenation to produce light olefins, with a 36.1% selectivity toward C2=-C4= products at a 49.6% conversion and an unprecedentedly high iron time yield for CO2 conversion to light olefins (∼29.1 μmolCO2·gFe−1·s−1) at the gaseous hourly space velocity of 24000 mL·gcat−1·h−1. In combination with structural characterizations and reaction results, it was unveiled that during the CO2 hydrogenation over ternary ZnCoxFe2-xO4 catalysts, the formation of electron-rich Fe0 atoms in the CoFe alloy phase significantly promoted in situ the generation of active iron-cobalt carbide, Co2C, and θ-Fe3C phases, thereby improving the reactivity of catalysts for the production of hydrocarbons and simultaneously inhibiting both the CO2 methanation and the secondary hydrogenation of olefins. The present findings provide a clear understanding of the roles of Fe-Co interactions over ternary ZnCoxFe2-xO4 catalysts for the highly efficient hydrogenation of CO2 to produce light olefins.