Using a multi-technical approach, we studied the oxidation of anatase TiO₂(1 0 1)-supported vanadium (V) clusters at room temperature. We found by ex situ XPS that the highest oxidation state is +4 at sub-monolayer coverage regardless of the O₂ pressure, and STM studies revealed that the initial oxidation proceeds through oxygen-induced disintegration of V clusters into monomeric VO₂ species. By contrast, for ∼2 monolayer V coverage, a partial oxidation to V⁵⁺ is achieved. By in situ APXPS measurements, we found that V can be maintained in the V⁵⁺ oxidation state irrespective of the coverage; however, in the sub-monolayer range, an O₂ pressure of at least ∼1 × 10⁻⁵ mbar is needed. Our results suggest an enhanced reducibility of V in direct contact with the TiO₂ support compared to V in the 2nd layer, which is in line with the observed optimum V₂O₅ loading in catalytic applications just slightly below a full monolayer.

使用多种技术的方法，我们研究了在室温下锐钛矿型TiO ₂（1 0 1）负载的钒（V）团簇的氧化。我们通过异位XPS发现，无论O ₂压力如何，在亚单层覆盖下，最高氧化态均为+4 ，而STM研究表明，初始氧化是通过氧诱导的V团簇分解为单体VO ₂物种而进行的。相比之下，对于〜2个单层V覆盖，可以实现部分氧化为V ⁵⁺。通过原位APXPS测量，我们发现V可以保持V ⁵⁺氧化态，而与覆盖率无关。但是，在亚单分子层范围内，O ₂需要至少约1×10 ^-5 mbar的压力。我们的结果表明，与第二层中的V相比，与TiO ₂载体直接接触的V的还原性得到了增强，这与在催化应用中观察到的最佳V ₂ O ₅负载略低于全单层的情况相符。