Materials for Energy Conversion and Storage, Department of Chemical Engineering, Delft University of Technology, The Netherlands.
J Am Chem Soc. 2012 Jun 6;134(22):9369-75. doi: 10.1021/ja302246b. Epub 2012 May 29.
Conventional TiO(2)-based photocatalysts oxidize NO(x) to nitrate species, which do not spontaneously desorb and therefore deactivate the catalyst. We show that the selectivity of this reaction can be changed by creating a large concentration of oxygen vacancies in TiO(2) nanoparticles through thermal reduction in a reducing atmosphere. This results in the photoreduction of nitric oxide (NO) to N(2) and O(2), species which spontaneously desorb at room temperature. The activity of the photoreduction reaction can be greatly enhanced by doping the TiO(2) nanoparticles with Fe(3+), an acceptor-type dopant that stabilizes the oxygen vacancies. Moreover, the photoinduced reduction of Fe(3+) to Fe(2+) provides a recombination pathway that almost completely suppresses the formation of NO(2) and thus enhances the selectivity of the reaction for N(2) formation. Gas chromatography confirms that N(2) and O(2) are formed in a stoichiometric ratio, and the activity for NO decomposition is found to be limited by the concentration of oxygen vacancies. A series of internally consistent reaction equations are proposed that describe all experimentally observed features of the photocatalytic process. The observed influence of oxygen vacancies on the activity and selectivity of photoinduced reactions may lead to new routes toward the design of highly selective photocatalysts.
传统的 TiO(2) 基光催化剂将 NO(x) 氧化为硝酸盐物种，这些物种不会自发解吸，从而使催化剂失活。我们表明，通过在还原气氛中进行热还原在 TiO(2) 纳米粒子中创建大量的氧空位，可以改变该反应的选择性。这导致一氧化氮 (NO) 光还原为氮气 (N(2)) 和氧气 (O(2))，这些物质在室温下会自发解吸。通过用 Fe(3+)（一种受主型掺杂剂）掺杂 TiO(2) 纳米粒子，可以极大地增强光还原反应的活性，Fe(3+) 可以稳定氧空位。此外，光诱导的 Fe(3+) 还原为 Fe(2+) 提供了一种复合途径，几乎完全抑制了 NO(2) 的形成，从而提高了反应生成 N(2) 的选择性。气相色谱证实氮气 (N(2)) 和氧气 (O(2)) 以化学计量比形成，并且发现 NO 分解的活性受氧空位浓度的限制。提出了一系列内部一致的反应方程来描述光催化过程中所有观察到的实验特征。观察到的氧空位对光诱导反应活性和选择性的影响可能会导致设计高选择性光催化剂的新途径。
