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Yongxia Miao,Xiaohui Liu,Yanglong Guo,Yanqin Wang,Yun Guo,Guanzhong Lu 한국공업화학회 2010 Journal of Industrial and Engineering Chemistry Vol.16 No.1
The MoO3/SiO2 catalysts containing different surface molybdenum species were prepared by a sol–gel method, and the effects of the preparation condition and MoO3 loading on the surface molybdenum species and property of MoO3/SiO2 were studied. The XRD, FT-IR, UV–vis and Raman spectroscopies were used to characterize the surface molybdenum species, and temperature-programmed desorption of NH3 adsorbed on a catalyst was used to detect the surface acidic properties. The results show that, therewere the dispersed polymolybdate, a-MoO3, b-MoO3, monomeric molybdenum species and silicomolybdic acid on the MoO3/SiO2 catalyst, and their distributions and subsistence states were affected by the preparation condition and MoO3 loading. Different molybdenum species exhibit different catalytic activities for the epoxidation of propylene with cumene hydroperoxide. In the 15 wt% MoO3/SiO2 catalyst synthesized at pH 9.1 and dried appropriately, there are the small size b-MoO3 and monomeric molybdenum species that they are mainly effective catalyst components for the epoxidation of propylene. Using this catalyst, the ~100% conversion of cumene hydroperoxide and ~100% selectivity to propylene oxide can be obtained in the tert-butyl alcohol solvent at 2.6 MPa and 80 8C for 4 h.
Zengzan Zhu,Yun Guo,Yanglong Guo,Zhigang Zhang,Yanqin Wang,Guanzhong Lu 한국공업화학회 2012 Journal of Industrial and Engineering Chemistry Vol.18 No.6
The properties and stabilities of Pd/Al2O3 close-coupled catalysts prepared with different methods and Pd precursors (PdCl2, Pd(NO3)2, and Pd(NH3)2(NO2)2) have been investigated, and characterized by N2adsorption at low temperature, H2 chemical adsorption, X-ray diffraction (XRD), H2 temperature programmed reduction (H2-TPR), transmission electron microscopy (TEM) and three-way catalytic activity testing. The results show that the catalyst prepared by a prefabricate method with Pd(NH3)2(NO2)2 precursor behaves higher catalytic activity and thermal stability for removing HC, CO and NOx, due to its higher BET surface area, higher Pd dispersion, smaller Pd particle sizes. And the prefabricate method can lead to stronger interaction between the Pd active species and the support by means of a strong electrostatic attraction and ion/ligand-exchange between the Pd complexes and the support surface, which restrict the remotion and sintering of Pd active particles at high temperature. Therefore, a prefabricate method is more suited to preparing close-coupled catalysts than a traditional impregnation method.