Tailoring materials by high-energy ball milling: TiO2 mixtures for catalyst support application

Abstract

We carried out a rational design of catalyst supports by high-energy ball milling. Tailored mixtures of TiO2 crystalline phases were obtained using rotational speed and milling time as variable parameters. Polymorphic transformation from anatase to rutile through high-pressure TiO2 (II) as intermediate was confirmed by X-ray Diffraction (XRD), Raman Spectroscopy and Transmission Electron Microscopy (TEM). Also, starting material doubled its specific surface area due to particle fragmentation, as confirmed by surface area of Brunauer-Emmet-Teller (SBET) and Scanning Electron Microscopy (SEM). Defects introduced during milling process generated oxygen vacancies in the surface and bulk of supports, as evidenced by X-ray Photoelectron Spectroscopy (XPS) and Electron Paramagnetic Resonance (EPR). Furthermore, longer milling time increased reducibility and oxygen mobility of supports, as observed by H2 Temperature Programmed Reduction (H2-TPR) and O2 Temperature Programmed Desorption (O2-TPD). Phase composition remained unchanged even under extreme conditions, highlighting the stability of unusual TiO2 (II) phase. Properties achieved in present materials could benefit metal-support interactions and play a major role in supported catalysts.