This work investigated the catalytic high‐pressure CO2 pretreatment of giant reed. CO2 is a renewable resource; its use does not generate chemical wastes and it can be easily removed and recycled. The effect of the addition of low concentrations of FeCl3 (0.16 wt %) and PEG 400 (1.0 wt %) on the hemicellulose hydrolysis to xylose and xylo‐oligosaccharides (XOS) is reported for the first time. Under the optimised pretreatment conditions, the xylan conversion of 82 mol % and xylose and XOS yields of 43 and 20 mol % were achieved, respectively. The solid residues obtained from different pretreatments were used as the substrate for the enzymatic hydrolysis to give glucose. The total glucose yield achieved under the optimised two‐step process was 67.8 mol % with respect to the glucan units in the biomass. The results demonstrated that PEG‐assisted FeCl3‐catalysed scCO2 pretreatment can produce xylose‐ or XOS‐rich hydrolysates and improve the enzymatic hydrolysis of biomass.

The cover feature image represents the role of carbon dioxide in the proposed biorefinery scheme based on CO2 capture by lignocellulosic biomass and the use of supercritical CO2 for the efficient pretreatment of giant reed under sustainable reaction conditions. The synergistic combination of supercritical CO2, FeCl3 and surfactant PEG400 allowed to selectively produce second‐generation sugars such as glucose, xylose or xylo‐oligosaccharides, which represent value‐added platform chemicals. More information can be found in the Research Article by N. Di Fidio, A. M. Raspolli Galletti, and co‐workers.