The influence of bulk stoichiometry on near-ambient pressure reactivity of bare and Pt-loaded rutile TiO ₂ (110)

The interaction of catalyst particles with reducible support materials can drastically change their reactivity. On rutile TiO₂, processes like particle encapsulation (caused by the "strong metal-support interaction", SMSI) have long been known to depend on the initial reduction state of the oxide. Despite this knowledge, sample stoichiometry has rarely been controlled in a reproducible manner in the surface science literature. Here, we use scanning tunnelling microscopy (STM) to explore systematically how near-ambient pressures (0.1-1.0 mbar) of O₂, H₂, CO and CO₂ affect blank and Pt-loaded rutile TiO₂(110) surfaces of different bulk stoichiometry at 600 K. To this end, we present preparation recipes that result in a sample stoichiometry always converging back to the same value, which allows us to use the same samples with constant reduction state over hundreds of preparation cycles. Comparing a highly reduced and a near-stoichiometric TiO₂ sample, we find that surface reactivity to all four gasses differs even without Pt loading. Most surprisingly, we find that the highly reduced TiO₂(110) is oxidized by CO₂, but this reaction is completely inhibited on the near-stoichiometric sample. Pt nanoparticles, in turn, become encapsulated after vacuum annealing on the reduced, but not on the near-stoichiometric sample. Encapsulation on the near-stoichiometric sample is achieved only after exposing it to 0.1 mbar H₂ at 600 K. Interestingly, we also see a further modification of the already encapsulated particles on the reduced sample under the same conditions, such that they become embedded deeper in the TiO₂(110) surface.