Molten‐Salt MgCl ₂ Modification of Microalgae‐Derived Biochar for Product Upgrading of Microalgae Pyrolysis

Biochar catalysts are widely applied in biomass pyrolysis, while molten salt modification offers a cost‐effective, recyclable alternative. However, for nitrogen‐rich microalgae feedstocks, catalyst tuning that improves upgrading selectivity remains needed. In this study, Chlorella biochar was modified using magnesium chloride (MgCl 2 ) molten salt, and the effects of treatment temperature and salt ratio on its structure were investigated. The modified biochar was further employed to catalyze Chlorella pyrolysis via PY‐GC/MS pyrolysis–gas chromatography/mass spectrometry (PY‐GC/MS). Results showed that biochar yield decreased with rising temperature, with 800°C producing the optimal structure. Excessive temperature suppressed pore development, whereas higher salt ratios improved graphitization. The biochar prepared at a 1:6 (biochar:salt, 1/6) ratio exhibited the best lamellar structure. Thermogravimetric analysis confirmed that the catalyst reduced char yield, enhanced surface activity, and shifted the pyrolysis peak. Thermogravimetric (TG) analysis indicated that the catalyst altered the thermal decomposition behavior, including a shift in the main pyrolysis peak. Catalytic activity was positively correlated with surface area, leading to a significant increase in hydrocarbons (30.58%) and aromatics, while reducing acidic compounds. These findings provide guidance for developing recyclable and low‐cost catalysts for biomass pyrolysis.