Design of Highly Active Photocatalytic System for the Removal of NOx

减少NOx和SOx造成的全球大气污染是当前一项紧迫而严峻的挑战。光催化技术在气固体系中的应用也很有前景。本课题研究发现，用离子交换法制备的二氧化硅(Cu^&lt；2+&gt；/SiO_2)和Y型沸石(Cu^&lt；2+&gt；/Y-沸石)负载的Cu^&lt；2+&gt；/Y沸石样品在高于573K的温度下被抽真空，二氧化硅(Cu^+/SiO_2)和Y沸石(Cu^+/Y-沸石)催化剂上还原的Cu^+离子在275K时可以光催化和化学计量比地将NO分子分解为N_2和O_2。在275K时，紫外光照射(270 Nm)导致NO分解为N_2和O_2。在275K紫外光照射下，NO的主要分解过程是线性的NO分解产物为N_2和O_2，少量生成N_2…较多的O和NO_2。这些次要产物被发现是N、O和NO的二次产物，整个反应是化学计量反应。因此，这些结果清楚地表明，在有NO存在的情况下，紫外光照射使Cu2+/SiO_2催化剂(或Cu^+/Y-沸石)在275K时将NO光催化分解为N_2和O_2。通过对吸附在铜离子上的铜(Cu^&lt；2+)离子和NO物种的ESR测量和铜(Cu^++)离子激发态(3d^94s^1电子态)的动态光致发光分析，研究了固定在SiO_2和Y-沸石上的Cu~(++)离子的物理化学性质和光化学性质。这些结果表明，铜离子(Cu2+)的激发态在光催化分解NO分子中起着重要的作用，在其激发态寿命内，光反应涉及到电子从激发态向NO分子的反键轨道的转移。因此，目前在Cu2+/SiO_2和Cu^+/Y沸石催化剂上的研究结果表明，它们有可能在常温下将NOx直接分解为N_2和O_2。较少

Reducing global air pollution caused by NOx and SOx is currently an urgent and serious challenge. Utilization of photocatalytic processes in gas-solid systems also promising. In the present project, we have studied and found that Cu^<2+> ions supported on silica (Cu^<2+>/SiO_2) and Y-Zeolite (Cu^<2+>/Y-Zeolite) prepared by an ion-exchange method are easily reduced to Cu^+ ions when the Cu^<2+>/SiO_2 and Cu^<2+>/Y-Zeolite samples are evacuated at temperatures higher than 573 K and the reduced Cu^+ ions on silica (Cu^+/SiO_2) and Y-Zeolite (Cu^+/Y-Zeolite) catalysts can decompose NO molecules photocatalytically and stoichiometrically into N_2 and O_2 at 275 K.UV irradiation ( 270 nm) of the Cu^+/SiO_2 and Cu^+/Y-Zeolite catalysts in the presence of NO molecules at 275 K was found to lead to the decomposition of NO into N_2 and O_2. Decomposition of NO proceeds linearly with UV irradiation time at 275 K. The major products of NO decomposition were N_2 and O_2 with a minor formation of N_2 … More O and NO_2. These minor products were found to be secondary products of N, O, and NO, and the overall reaction was found to be stoichiometrical. Thus, these results clearly indicate that UV irradiation of the CU^+/SiO_2 catalyst (or Cu^+/Y-Zeolite) in the presence of NO leads to the photocatalytic decomposition of NO into N_2 and O_2 at 275 K.The physicochemical and photochemical properties of Cu^+ ions anchored onto SiO_2 and Y-Zeolite have been investigated by means of ESR measurements of the copper (Cu^<2+>) ions and of NO species adsorbed on the copper ions and dynamic photoluminescence measurements of the excited state of the copper (Cu^+) ions (3d^94s^1 electronic state), as well as product analysis of photodecomposition of NO molecules. These results indicate that the excited state of copper ions (Cu^+ ions) plays a significant role in the photocatalytic decomposition of NO molecules and the photoreaction involves an electron transfer from the excited state of the Cu^+ ion into an anti-bonding orbital of NO molecule within the lifetime of its excited state.Thus, the present results obtained with the Cu^+/SiO_2 and Cu^+/Y-Zeolite catalysts imply the possibility of their utilization as a potentially promising type of photocatalysts for the direct decomposition of NOx into N_2 and O_2 at around normal temperature. Less