From vanadia nanoclusters to ultrathin films on TiO2(110): Evolution of the yield and selectivity in the ethanol oxidation reaction

Oxide-on-oxide systems are becoming increasingly important in nanocatalysis and surface engineering, because of the creation of hybridized interfaces holding high reactivity and selectivity toward oxidation reactions. Here we report on the results of a multitechnique surface science study conducted on an oxide/oxide model system. By depositing increasing amounts of vanadium oxide (VOx) on a titanium dioxide-rutile(110) substrate, we were able to follow the morphology and oxidation state of the overlayer. Three growth modes were detected: nanoclusters at low coverage (0.3 and 0.5 monolayer), one-dimensional strands aligned along the substrate [001] direction at monolayer coverage, and three-dimensional nanoislands at higher coverage (2.0 and 5.0 monolayers). All these structures share the same oxidation state (V2O3). We studied the reactivity and selectivity of these model catalysts toward partial oxidation of ethanol, finding that both of them depend on the VOx thickness. Nanoclusters can yield acetaldehyde through low-temperature oxidative dehydrogenation but show a scarce selectivity in the investigated temperature range. The monolayer coverage is the most reactive toward ethanol dehydration to ethylene, showing also good selectivity. Similar results are found at high coverage, although the overall reactivity of the systems toward alcohol oxidation decreases.