Atomically dispersed Co2+ on MgAlOx boosting C4–10 alcohols selectivity of ethanol valorization

Abstract

Catalytic upgrading of biomass-derived ethanol to C₄₊ compounds through C–C coupling is an essential green and sustainable approach towards value-added fine chemicals. Developing catalysts to improve the selectivity of C₄₊ compounds is highly desired due to the complex transformation of ethanol affording diverse species. Here, we report atomically dispersed Co²⁺ on MgAlO_x as catalysts derived from layered double hydroxide (LDH) precursors for the dehydrogenation coupling of ethanol to C_4–10 alcohols. The selectivity for C_4–10 alcohols reaches 95.4% with 32.9% ethanol conversion over the optimal catalyst, Co_0.15Mg_2.85AlO_x, at 523 K and 0.1 MPa. A yield of 31.4% is greatly higher than that (∼15%) over most of the state-of-the-art catalysts. Characterization techniques including XRD, XPS, UV-Vis and CO-IR reveal that the atomically dispersed Co²⁺ in the lattice of MgAlO_x is originated from the replacement of Mg in the LDH precursor and remain stable during the reactions. Both increments of basic and acid sites are observed after Co²⁺ replacement according to the TPD-MS measurements of CO₂ and NH₃. The introduction of an appropriate amount of Co²⁺ effectively facilitates the dehydrogenation step, thus, high activity under milder conditions. Meanwhile, abundant basic and acid sites boost the following aldol condensation step resulting in ultra-high C_4–10 selectivity. These findings can shed light on sustainable heterogeneous catalytic processes.