Gervasini Antonella, Manzoli Maela, Martra Gianmario, Ponti Alessandro, Ravasio Nicoletta, Sordelli Laura, Zaccheria Federica
Dipartimento di Chimica Fisica ed Elettrochimica & Centro di Eccellenza CIMAINA, Università degli Studi di Milano, via C. Golgi 19, 20133 Milan, Italy.
J Phys Chem B. 2006 Apr 20;110(15):7851-61. doi: 10.1021/jp056604c.
Copper catalysts prepared by chemisorption-hydrolysis technique over silica (Cu/Si) and silica-alumina (Cu/SiAl) supports were studied to understand the role of the support on the nature and surface properties of the copper species stabilized on their surfaces. The morphological and surface properties of the copper phases have been characterized by complementary techniques, such as HRTEM, EXAFS-XANES, EPR, XPS, and FTIR. For the FTIR investigation, molecular probes (CO and NO) were also adsorbed on the surfaces to test the reactivity of the copper species. Moreover, the catalytic performances of the two catalysts have been compared in the HC-SCR reaction (NO reduction by C(2)H(4)) performed in highly oxidant conditions. The superior activity and selectivity of the supported silica-alumina catalyst with respect to that supported on silica could be related with the different nature of the copper species stabilized on the two supports, as emerged from the results obtained from the spectroscopic investigations. Small and well-dispersed CuO particles were present on silica, whereas isolated copper ions predominated on silica-alumina, likely in regions rich in alumina that made some exchangeable sites available, as indicated by FTIR spectra of adsorbed CO. The less positive global charge of copper species on Cu/SiAl than in Cu/Si has been confirmed by EPR, XPS, and EXAFS-XANES analyses.
通过化学吸附-水解技术在二氧化硅（Cu/Si）和硅铝酸盐（Cu/SiAl）载体上制备的铜催化剂，被用于研究载体对稳定在其表面的铜物种的性质和表面性质的作用。铜相的形态和表面性质已通过诸如高分辨率透射电子显微镜（HRTEM）、扩展X射线吸收精细结构- X射线吸收近边结构（EXAFS-XANES）、电子顺磁共振（EPR）、X射线光电子能谱（XPS）和傅里叶变换红外光谱（FTIR）等互补技术进行了表征。对于FTIR研究，分子探针（CO和NO）也被吸附在表面以测试铜物种的反应活性。此外，在高氧化条件下进行的碳氢化合物选择性催化还原反应（C₂H₄还原NO）中，对这两种催化剂的催化性能进行了比较。从光谱研究结果可以看出，负载在硅铝酸盐上的催化剂相对于负载在二氧化硅上的催化剂具有更高的活性和选择性，这可能与稳定在两种载体上的铜物种的不同性质有关。在二氧化硅上存在小且分散良好的CuO颗粒，而在硅铝酸盐上，孤立的铜离子占主导地位，可能存在于富含氧化铝的区域，这使得一些可交换位点可用，吸附CO的FTIR光谱表明了这一点。EPR、XPS和EXAFS-XANES分析证实了Cu/SiAl上的铜物种的整体电荷比Cu/Si上的更正性更弱。
