Title : On the importance of supports when designing supported catalysts. The case of TiO2 polymorphic mixes
Recent studies have reported the importance of supports in heterogeneous catalysis, since their role is not limited to act as carriers for metal particles. There is evidence that support’s nature, crystalline phase and physicochemical properties could enhance catalytic performance during reaction. In this line, TiO2 is a well-known reducible oxide in catalysis since it can be used as promoter, carrier for metals and catalyst itself. Furthermore, titania is particularly used as support due to its low-cost, strong oxidizing power and great metal-support interaction. Hence, we propose a rational design of TiO2 mixtures for catalyst support application. We also present the high-energy ball milling as an effective technique to prepare tailored mixtures of titania phases, including anatase, rutile and high-pressure TiO2 (II), as confirmed by X-ray Diffraction (XRD), Raman Spectroscopy and Transmission Electron Microscopy (TEM). Starting material could double 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). Moreover, 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 severe conditions, highlighting the stability of unusual TiO2 (II) phase. Solids with enhanced physicochemical properties reported in this work could be successfully used as catalyst supports for oxidation reactions. Pd/TiO2 catalysts prepared with these supports are being tested in glycerol selective oxidation in liquid phase to study its effects in metal-support interaction and catalytic performance.
- We present high-energy ball milling as a simple and eco-friendly method of synthesis and/or modification of materials.
- We also highlight the need of considering support’s design when it comes to supported catalysts, since it could enhance catalytic performance under specific reactions.
- Defective structures and polymorphic mixes of anatase, rutile and TiO2 (II), induced by milling, could change physicochemical and catalytic properties of solids affecting future metal-support interactions.
- Obtained materials with distinctive features could be suitable as catalytic supports in oxidation reactions.