Hydroxy-induced cobalt oxides for syngas to light olefins

Light olefins-ethylene, propylene and butylene (C₂⁼-C₄⁼)-are essential building blocks in the chemicals industry and are traditionally produced by thermal or catalytic cracking of hydrocarbon feedstocks. Directly converting syngas (CO and H₂) into light olefins under mild conditions is attractive but challenging^1-4. Prismatic cobalt carbide (Co₂C) and associated hydrophobic modifications have shown potential for selective light-olefin synthesis under mild conditions^5,6. Here we show another hydrophilic-promotion strategy in which a set of hydroxy promoters, exemplified by hydroxyapatite (Ca₅(PO₄)₃(OH), HAP), fumed silica (SiO₂(F)) and amorphous boehmite (AlO(OH), AB), is physically mixed with a Co₂MnO₄ precursor, inducing synergistic cobalt-manganese (Co-Mn) oxides and Co₂C for syngas conversion. The induced anorthic Co-Mn oxides may serve as active phase for adsorbed-hydrogen-assisted CO dissociation to CH_x/CH_xO intermediates, whereas induced Co₂C or the Co₂C-oxide interface may mediate C-C coupling of these intermediates to form light olefins. This design achieved 70-82% CO conversion with light-olefins selectivity of more than 60% at 250-260 °C, 0.1 MPa with H₂/CO ratios of 1-2, giving light-olefins carbon utilization efficiency up to 13%, among the highest reported for syngas to light olefins. This simple hydrophilic strategy for facilitating CO activation may provide useful insights for improving industrial Fischer-Tropsch processes.