In situ quick X-ray absorption spectroscopy(QXAFS) at the Cu and Zn K-edge under operando conditions has been used to unravel the Cu/Zn interaction and identify possible active site of CuO/ZnO/Al_2O_3 catalyst for met...In situ quick X-ray absorption spectroscopy(QXAFS) at the Cu and Zn K-edge under operando conditions has been used to unravel the Cu/Zn interaction and identify possible active site of CuO/ZnO/Al_2O_3 catalyst for methanol synthesis. In this work, the catalyst, whose activity increases with the reaction temperature and pressure, was studied at calcined, reduced, and reacted conditions. TEM and EDX images for the calcined and reduced catalysts showed that copper was distributed uniformly at both conditions. TPR profile revealed two reduction peaks at 165 and 195 °C for copper species in the calcined catalyst. QXAFS results demonstrated that the calcined form consisted mainly of a mixed Cu O and Zn O, and it was progressively transformed into Cu metal particles and dispersed Zn O species as the reduction treatment. It was demonstrated that activation of the catalyst precursor occurred via a Cu^+intermediate, and the active catalyst predominantly consisted of metallic Cu and Zn O evenunder higher pressures. Structure of the active catalyst did not change with the temperature or pressure, indicating that the role of the Zn was mainly to improve Cu dispersion.This indicates the potential of QXAFS method in studying the structure evolutions of catalysts in methanol synthesis.展开更多
ZnO/SiO\-2 and ZnO\|SiO\-2 catalysts were prepared by the impregnation and sol\|gel method, respectively. The characterization of the catalysts by XPS and FTIR indicated that much "free" zinc oxide and unrea...ZnO/SiO\-2 and ZnO\|SiO\-2 catalysts were prepared by the impregnation and sol\|gel method, respectively. The characterization of the catalysts by XPS and FTIR indicated that much "free" zinc oxide and unreacted Si\_OH existed on the surface of ZnO/SiO\-2 sample. As for ZnO\|SiO\-2 sol\|gel catalyst, the corresponding phenomena were not observed. The prepared samples were also used as the catalysts for decomposition of 2\|butanol. A high selectivity for dehydrogenation was observed over the supported catalyst. However, a high selectivity for dehydration was shown over the ZnO\|SiO\-2 sol\|gel catalyst. The opposite selectivity for dehydration or dehydrogenation observed over the two kinds of catalysts may be just because of the different surface structures of the catalysts.展开更多
基金supported by the National Basic Research Program of China(973 Program,2013CB933104)the National Natural Science Foundation of China(Nos.11275258 and 11135008)
文摘In situ quick X-ray absorption spectroscopy(QXAFS) at the Cu and Zn K-edge under operando conditions has been used to unravel the Cu/Zn interaction and identify possible active site of CuO/ZnO/Al_2O_3 catalyst for methanol synthesis. In this work, the catalyst, whose activity increases with the reaction temperature and pressure, was studied at calcined, reduced, and reacted conditions. TEM and EDX images for the calcined and reduced catalysts showed that copper was distributed uniformly at both conditions. TPR profile revealed two reduction peaks at 165 and 195 °C for copper species in the calcined catalyst. QXAFS results demonstrated that the calcined form consisted mainly of a mixed Cu O and Zn O, and it was progressively transformed into Cu metal particles and dispersed Zn O species as the reduction treatment. It was demonstrated that activation of the catalyst precursor occurred via a Cu^+intermediate, and the active catalyst predominantly consisted of metallic Cu and Zn O evenunder higher pressures. Structure of the active catalyst did not change with the temperature or pressure, indicating that the role of the Zn was mainly to improve Cu dispersion.This indicates the potential of QXAFS method in studying the structure evolutions of catalysts in methanol synthesis.
文摘ZnO/SiO\-2 and ZnO\|SiO\-2 catalysts were prepared by the impregnation and sol\|gel method, respectively. The characterization of the catalysts by XPS and FTIR indicated that much "free" zinc oxide and unreacted Si\_OH existed on the surface of ZnO/SiO\-2 sample. As for ZnO\|SiO\-2 sol\|gel catalyst, the corresponding phenomena were not observed. The prepared samples were also used as the catalysts for decomposition of 2\|butanol. A high selectivity for dehydrogenation was observed over the supported catalyst. However, a high selectivity for dehydration was shown over the ZnO\|SiO\-2 sol\|gel catalyst. The opposite selectivity for dehydration or dehydrogenation observed over the two kinds of catalysts may be just because of the different surface structures of the catalysts.
