Integrated catalytic co-pyrolysis of microalgae-hardwood over CuO/NiO/MoO3-HZSM-5: Bio-oil upgrading and reuse of catalyst-loaded biochar for dye removal

Abstract

This study proposes an integrated dual-valorization strategy that combines catalytic co-pyrolysis of microalgae ( Scenedesmus sp.) and hardwood for bio-oil upgrading with the reuse of catalyst-loaded biochar for wastewater treatment. A CuO/NiO/MoO 3 /HZSM-5 hybrid catalyst was developed and evaluated in both in-situ and ex-situ catalytic configurations to elucidate their roles in bio-oil upgrading and product distribution. Catalyst characterization confirmed the preservation of the crystalline MFI structure of HZSM-5 and uniform dispersion of metal oxides with high thermal stability. At 500 °C, non-catalytic co-pyrolysis of a 1:1 microalgae–hardwood blend produced 22.1 wt% bio-oil, which increased to 23.9 wt% (in-situ) and 23.5 wt% (ex-situ) with catalytic upgrading. Catalysis significantly improved bio-oil quality by reducing oxygen- and nitrogen-containing compounds, increasing carbon and hydrogen contents, and enhancing the higher heating value to 25.27 MJ kg −1 . Comparative analysis revealed that ex-situ catalysis favored the formation of aromatic hydrocarbons and phenolic compounds, while in-situ catalysis produced bio-oil with higher energy density. Importantly, the catalyst-loaded biochar generated during in-situ co-pyrolysis exhibited a negative surface charge (−21.6 mV) and excellent adsorption performance for methylene blue, achieving 96.6% removal (144.9 mg g −1 ) within 40 min and maintaining >92% efficiency after five regeneration cycles. These findings demonstrate a single-process pathway for simultaneous production of upgraded bio-oil and functional adsorbent materials, contributing to sustainable bioenergy production and wastewater remediation within a circular bioeconomy framework. • Catalytic co-pyrolysis of microalgae–hardwood over CuO/NiO/MoO 3 /HZSM-5. • In-situ and ex-situ catalysis compared for bio-oil yield and composition. • Catalysis improved HHV and promoted aromatic hydrocarbons in bio-oil. • Catalyst-loaded biochar removed 96.6% methylene blue from wastewater. • Integrated process enables dual valorization of bio-oil and biochar.