Abstract

The design of efficient solid acid catalysts for biomass‑derived sugar conversion requires precise control over surface acidity and stability under hydrothermal conditions. Herein, a composition‑tunable series of titanium oxide–phosphate (xP-Ti) nanocatalysts with well‑defined Ti⁴⁺–O–P networks was synthesized via a hydrothermal method and evaluated for aqueous–phase xylose dehydration to furfural. By systematically varying phosphate content, an optimal catalyst (4.0P-Ti) was identified, achieving a furfural yield of up to 56% at 170 °C under single–phase water conditions. Structural and spectroscopic analyses reveal that phosphate incorporation induces disordered Ti–O–P networks, generating synergistic Brønsted and Lewis acid sites while maintaining stability under hydrothermal conditions. Correlation of these properties with catalytic performance demonstrates that furfural selectivity is governed by a balance between acid‑site density, acid strength, and accessibility, rather than surface area alone. In situ infrared spectroscopy and density functional theory calculations provide supporting evidence for energetically favored dehydration pathways and adsorption–desorption behavior consistent with enhanced furfural formation, without implying direct identification of transient intermediates. The 4.0P-Ti catalyst exhibits good recyclability, with reversible carbonaceous deposition identified as the primary deactivation pathway. It was remarked that this work establishes a clear structure-acidity-performance relationship and highlights titanium oxide–phosphate materials as robust solid acid catalysts for selective furfural production in water.