Hydrothermal conversion of paddy residue into bio-oils and chemicals using pure and zirconium-doped cerium oxide nanocatalysts

The depletion of fossil fuel reserves has intensified research into renewable and sustainable energy sources, with biomass receiving considerable attention due to its abundance and carbon neutrality. In this work, paddy straw was converted into bio-oils and value-added chemicals through catalytic hydroliquefaction using CeO2 and Zr-doped CeO2 (Zr–CeO2) nanocatalysts (NCs). The NCs were synthesized via a hydrothermal method and systematically characterized. XRD patterns confirmed the formation of a single-phase cubic fluorite structure for both catalysts. HR-TEM analysis revealed nanosized particles with clear lattice fringes, improved crystallinity, and reduced agglomeration after Zr incorporation. FT-IR spectra showed characteristic Ce–O and Zr–O–Ce vibrational bands, confirming successful Zr substitution within the CeO2 lattice. Under optimized conditions (temperature: 200 °C, reaction time: 10 h, catalyst loading: 100 mg), Zr–CeO2 achieved a biomass conversion of 87.9 % and a bio-oils yield of 68.3 %, significantly higher than those obtained with pristine CeO2 (82.1 % conversion, 66.2 % bio-oils yield). GC–MS analysis indicated that the bio-oils mainly consisted of alcohols, phenols, acids, esters, ketones, hydrocarbons, and furans. The enhanced performance is attributed to Zr-induced lattice modification and improved dispersion of active sites, representing a novel catalytic enhancement strategy for efficient paddy straw hydroliquefaction.