High entropy alloy formation derived from high entropy oxide: unlocking the active sites for green methanol production from CO₂

Abstract

In pursuit of novel materials for CO₂ conversion to value-added chemicals, previous research has predominantly focused on copper-based, indium oxide (In₂O₃)-based, and alloy or intermetallic materials. However, a groundbreaking approach is presented by introducing a high-entropy-based material for CO₂ reduction to methanol (CH₃OH). This method offers scalability and simplicity, making it feasible for large-scale production of high-entropy-alloys (HEAs). The formation of HEA is facilitated by the presence of Fe, leads to the creation of a high-entropy oxide (HEO) during calcination. Through X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS), comprehensively analyzed the oxidation states and coordination environments of all metals in both HEO and HEA. The formation of Fe₃O₄ within the HEO structure is evident, with each metal occupying either tetrahedral (T_d) or octahedral (O_h) sites. The HEA formed shows exceptional CO₂ conversion efficiency and higher CH₃OH selectivity. Isolated sites of Co, Ni with Fe, Cu, and Zn, along with CuZn pair, are considered as the active sites for CO₂ to CH₃OH and further determined by DFT calculations. The altered reaction mechanism upon HEA formation compared to individual metals is investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Finally, Life-cycle assessment (LCA) indicates the carbon-negative footprint.