Interactions of VOx Species with Amorphous TiO2 Domains on ALD-Derived Alumina-Supported Materials

Alumina-supported VOx-TiO2 materials are synthesized by atomic layer deposition (ALD) and characterized by diffuse reflectance UV-vis (DRUV-vis) spectroscopy, Raman spectroscopy, and density functional theory (DFT) calculations in order to identify the metal oxide structures present on the surface of the support. Preferential binding of VOx to TiO2 domains is demonstrated by Raman spectroscopy studies and confirmed by DFT. Varying distributions of V-O-Ti, V-O-V, and V-O-Al bonds are present in the examined materials. The interactions of VOx and TiO2 are elucidated further under a reducing, H-2 environment at elevated temperatures. An enhancement in reducibility of VOx species is expected and observed upon the modification of alumina with TiO2 above monolayer coverages, but also when a single ALD cycle of TiO2 is deposited following the deposition of VOx on the support. X-ray photoelectron spectroscopy (XPS) detects changes in the oxidation state of vanadium, but not titanium during reduction. Reversible migration and aggregation of V and Ti atoms is also detected upon heating in H-2.