The research offers insights into lignin valorization towards aromatic compounds, providing an alternative to burning and supporting sustainability goals. The study investigates the efficiency of CuO/TiO2 as a catalyst in the aerobic depolymerization of lignin from various botanical origins and extraction methods, focusing on the yield of aromatic compounds like vanillin. It highlights how the botanical origin and industrial extraction process of lignin affect its reactivity and structural behavior during depolymerization. Extensive characterization techniques are employed to outline structural differences in lignin, which are correlated with the catalytic reaction outcomes. The research aligns with sustainability goals by offering alternative lignin valorization pathways, potentially transforming paper mill industries into biorefineries and minimizing waste. These comments reflect the paper’s focus on advancing lignin valorization for sustainable aromatic compound production using copper-based catalysis.

In general, the language of the manuscript is original and concisely correct, the methods are adequate to the tasks claimed by authors and to the objects chosen for this study. Data interpretation included analysis of the literature data, including both the most recent papers in the field.

Here are some potentially confusing statements, which need to be addressed prior to being accepted:
- Elemental Analysis Discrepancy: The elemental analysis of KraftSoft 2 lignin shows a carbon content significantly higher than other lignins, which is unusual and might be confusing without further context.
- FTIR-ATR Interpretation: The FTIR-ATR spectra interpretation suggests that the pulping method did not induce remarkable structural modifications on the polymeric lignin structure, which could be perplexing given the expected impact of different pulping processes.
- 31P NMR Quantification: The quantification of oxygen in lignin as free hydroxyl groups using 31P NMR shows a lower content for OrganoHerb lignin, which might be confusing when trying to correlate with other structural analyses.
- TGA Analysis Consistency: The TGA analysis indicates that OrganoHerb lignin burns at a lower temperature compared to others, which could be confusing as it suggests a lower molecular weight that is not expected from organosolv lignin.
- Metal sustainability metrics. It is also advised to address, in certain extent, the metal sustainability metrics to highlight qualitative or a quantitative metrics of greenness for the processes discussed.