高分散Ce-g-C3N4/TiO2构筑及其光催化氧化NO与Hg0反应机理

Synergistic photo-oxidation of NO and Hg0 at low-temperature plays an important role in the reduction of the air pollutants of coal-fired power plants. Although a high photo-oxidation efficiency of NO or Hg0 can be reached by traditional Ce/Ti photocatalyst at low temperature, it is difficult to improve the synergistic photo-oxidation efficiencies of NO and Hg0 resulting from the inhibition of NO on the photo-oxidation of Hg0. This research aims to prepare highly dispersed single atom or ultra-small clusters of Ce embedded in the cavity of g-C3N4 to obtain photocatalyst of Ce-g-C3N4/TiO2. It surmounts the disadvantages of the low atomic efficiency and the inefficient separation of photoinduced electron-hole pair caused by the CeO2 aggregates and the partial overlap of the conduction band potentials of CeO2 and TiO2, respectively, which is beneficial to enhancing the photocatalytic activity and weakening the inhibition of NO on Hg0 oxidation in order to realize the efficient synergistic photo-oxidation of NO and Hg0. It investigates the structure-activity relationship between the loading form of Ce, the band structure and the photo-electrical properties of the photocatalyst; specifies the species and amount of free radicals, the main activated sites for the photo-oxidation and clarifies their influences on the enhancement of the synergistic photo-oxidation efficiency by surface characterization and removal test; analyzes the dominant photocatalytic oxidation path and figures out the synergistic photo-oxidation mechanism using the experimental results and quantum chemical calculation. Based on the analysis results, it will establish the preparation scheme of the efficient photocatalyst. Both the design of highly dispersed non-noble metal single-atom or ultra-small catalyst and the synergistic control of the multiple pollutants will be greatly developed due to the innovative ideas contributed by the accomplishment of this research.

低温光催化协同脱硝除汞是削减燃煤电厂大气污染物排放的重要方向。传统铈钛催化剂在低温下虽可高效光催化氧化NO或Hg0，但因NO对Hg0氧化的抑制，导致协同脱除效率低。本研究拟将Ce以单原子或超小团簇固定于g-C3N4空腔中，制备高分散Ce-g-C3N4/TiO2光催化剂。该催化剂可克服CeO2团聚引起的原子利用率低，及与TiO2导带电势部分重合不利光生电子与空穴分离的缺陷，提升催化剂活性，削弱NO对Hg0氧化抑制，实现低温高效协同脱硝除汞的目的。重点考察Ce负载形态、催化剂能带结构与催化剂光电性质的构效关系；通过表征分析和性能测试，明确催化反应过程中自由基的产生及关键活性位点，理清其对协同脱除效率的影响；结合实验结果与量子化学计算，分析光催化反应途径，阐明该催化剂光催化协同氧化机理，最终形成高效光催化剂的构筑方案。本项目可为非贵金属单原子或超小团簇催化剂的开发和多污染物协同控制提供新思路。

基于TiO2的改性催化剂对燃煤烟气中Hg0具有显著的氧化活性，如何提高表面活性中心的分散性，从而进一步提高改性TiO2的催化活性，成为汞催化去除领域的重要方向之一。研究以提高表面活性中心的分散程度且缩小其负载尺寸，进而提高催化剂的催化活性为目标，提出以g-C3N4作为锚定位点制备CeO2高分散超小团簇、以Ti4+缺陷位锚定Au单原子等调控策略，显著提高改性TiO2对Hg0的氧化作用。本研究深入剖析调控策略对表面活性中心存在状态的影响，高分散催化剂对提高TiO2催化活性的机制（光生电荷传输机制、载体晶格氧的氧化活性等），以及在烟气条件下对Hg0的氧化性能。本研究提出g-C3N4/TiO2作为高分散CeO2的负载载体，在g-C3N4/TiO2之间形成光生电子和空穴对的Z型以及CeO2与g-C3N4之间的II型传输机制，两种分离机制的复合加速了光生电子-空穴对的分离进而提高对Hg0的氧化性能；此外，以含有Ti4+缺陷位的TiO2锚定Au单原子制备O-Au-O配位结构，Au-O之间的弱配位作用显著提高表面晶格氧的氧化活性，进而提高Au单原子负载TiO2对Hg0的氧化性能。