SURFACE-STRUCTURE AND REACTIVITY OF MOLYBDENA TITANIA CATALYSTS PREPARED BY DIFFERENT METHODS

被引:27
作者
DELARCO, M
MARTIN, C
RIVES, V
SANCHEZESCRIBANO, V
RAMIS, G
BUSCA, G
LORENZELLI, V
MALET, P
机构
[1] UNIV GENOA,FAC INGEGNERIA,IST CHIM,I-16129 GENOA,ITALY
[2] UNIV SEVILLE,FAC QUIM,DEPT QUIM INORGAN,SEVILLE,SPAIN
来源
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS | 1993年 / 89卷 / 07期
关键词
D O I
10.1039/ft9938901071
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
MoO2-TiO2 samples have been prepared from aqueous solutions of ammonium heptamolybdate and titania (by conventional impregnation and equilibrium adsorption) and by mechanically mixing both oxides (with and without further hydrothermal treatment). The samples have been characterized by X-ray diffraction, specific surface area assessment, Fourier-transform infrared (FTIR) and ultraviolet-visible diffuse refectance (UV-VIS DR) spectroscopies and temperature-programmed reduction (TPR). Surface properties have been studied following the adsorption of probe molecules by FTIR spectroscopy. Dispersed phases are formed preferentially in samples prepared by equilibrium adsorption and in physical mixtures submitted to hydrothermal treatment; in all other cases crystalline MoO3 is mainly formed. Dispersed phases are more easily reduced. They have been identified as surface molybdenyl species bonded to Ti cations through bridging oxygens, and their overall coordination depends on the degree of surface hydration. These species predominate quantitatively on the catalyst surfaces and have been found to be strong Lewis and Bronsted acids. They are also more easily reduced than bulk MoO3 under TRP conditions, and very active as oxidizing agents for methanol.
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页码:1071 / 1078
页数:8
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