High-energy ball milling strategies for the synthesis of Cu/TiO₂ catalysts

Mechanochemical activation stands out as an eco-friendly and cost-effective solid-state technique for the synthesis of a variety of materials. Due to its simplicity and robustness, high-energy ball milling has become an efficient and greener alternative to improve physicochemical properties of solids, including an increase in Specific Surface Area (S_BET), ion mobility, oxygen vacancies, metal–support interactions and even the formation of new polymorphic structures, due to the accumulation of surface and structural defects and high pressure and temperature locally achieved.

In this work, Cu/TiO₂ catalysts were prepared by several high-energy ball milling strategies (dry milling and semi-wet milling) using different copper reagents and compared with a sample synthesized by a conventional impregnation method. Crystal structures were identified by means of X-ray Diffraction (XRD), including anatase, rutile, high-pressure TiO₂ (II), and W species due to mill vial erosion under some conditions. Specific Surface Area (S_BET) values were calculated from N₂ physisorption (BET method), indicating a correlation between the energy supplied to the powder and the milling conditions. Moreover, Scanning Electron Microscopy (SEM) showed the distinctive morphologies achieved, while a semi-quantification of present elements could be performed using Electron Diffraction Spectroscopy (EDS). Catalysts obtained through this green and one-pot process could be suitable for a variety of reactions, including CO₂ hydrogenation and glycerol hydrogenolysis.