Boosted benzyl alcohol photocatalytic esterification efficiency and tunable methyl benzoate selectivity by cocatalyst engineering over microspheric TiO2

Abstract

Methyl benzoate (MB) is a high-value fine chemical extensively used as a flavoring agent, fragrance component, solvent and synthetic intermediate in pharmaceuticals, coatings and agrochemicals. Conventional industrial routes to MB and related benzyl alcohol oxidation products often involve harsh conditions, toxic oxidants or corrosive acids, and suffer from high energy consumption, low atom economy and difficult product separation. Therefore, the development of efficient, low-cost, green and readily recyclable routes to MB is urgently needed. Photocatalysis, which exploits light to drive selective oxidation–esterification under mild conditions, offers a promising pathway toward this goal; however, current literature highlights several limitations that impede practical application—many high-activity systems rely on expensive noble or bimetallic catalysts prepared via complex, high-temperature multi-step protocols (increasing material and processing costs), most studies report high selectivity only to benzaldehyde rather than further transformation to MB or benzoic acid, and product separation/purification remains a significant engineering challenge.
In this work, we develop and evaluate a series of microspherical TiO₂-based photocatalysts (Au/TiO₂, Pd/TiO₂ and Pt/TiO₂) for the visible-light-driven oxidation–esterification of benzyl alcohol with the aim of delivering a scalable, selective route to MB. Catalysts were synthesized by hydrothermal methods followed by wet-impregnation and were characterized by SEM–EDS, TEM XRD, XPS, XAS, UV–Vis and i–t measurements to determine morphology, elemental dispersion, crystalline phase and surface electronic properties.
Photocatalytic performance, evaluated under identical conditions and benchmarked against commercial TiO₂ P25, exhibited pronounced dependence on the metal co-catalyst in both activity and product distribution. While bare TiO₂ yielded benzaldehyde at a rate of 39.21 μmol·g⁻¹·h⁻¹, metal-loaded samples showed significantly enhanced activity. The 0.75-Pd/TiO₂ catalyst produced BzH at 200.35 μmol·g⁻¹·h⁻¹, representing a 5.11-fold enhancement with a benzyl alcohol conversion of 24.59%. Similarly, 1.5-Pt/TiO₂ reached 330.72 μmol·g⁻¹·h⁻¹, corresponding to an 8.43-fold increase and a conversion rate of 5.68%. Most notably, 1.0-Au/TiO₂ demonstrated exceptional performance in methyl benzoate production, achieving an MB formation rate of 1005.31 μmol·g⁻¹·h⁻¹ with 33.09% benzyl alcohol conversion and 99.22% selectivity toward MB. This MB output represents a 25.6-fold enhancement relative to the BzH reference rate of unmodified TiO₂.
XPS/XAS and photoelectrochemical evidence supports a four-step synergistic pathway involving adsorption and alkoxide formation, metal-assisted dehydrogenation and O₂ activation (O₂→O₂•⁻), formation of hemiacetal/ester intermediates and product desorption. The catalysts exhibit reasonable recyclability under the tested conditions. These results provide mechanistic insight and a practical catalyst design strategy for green, selective photocatalytic production of methyl benzoate from benzyl alcohol.
To translate these findings toward practical production, future work will address pilot-scale testing in continuous photoreactors, rigorous long-term stability and metal-leaching studies, and strategies to reduce noble-metal content (e.g., single-atom sites, robust immobilization) while improving catalyst recyclability. Beyond MB synthesis, the optimized TiO₂-based platforms are extendable to other selective oxidations, photocatalytic tandem transformations and solar-driven environmental/energy applications, offering pathways to sustainable and economically viable photocatalytic manufacturing.

Date of Award	15 Jul 2026
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Honglei Zhang (Supervisor), Bencan Tang (Supervisor) & Qingxin Zhang (Supervisor)