The structure of active sites in Me-V-O catalysts (Me = Mg, Zn, Pb) and its influence on the catalytic performance in the oxidative dehydrogenation (ODH) of propane

被引:70
作者
Rybarczyk, P [1 ]
Berndt, H [1 ]
Radnik, J [1 ]
Pohl, MM [1 ]
Buyevskaya, O [1 ]
Baerns, M [1 ]
Brückner, A [1 ]
机构
[1] Inst Angew Chem Berlin Adlershofe EV, D-12489 Berlin, Germany
关键词
metal vanadate catalysts; oxidative dehydrogenation of propane; structure-reactivity relationships; in situ EPR; in situ UV/VIS; quasi in situ XPS;
D O I
10.1006/jcat.2001.3251
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
Me-V-O catalysts (Me = Mg, Zn, Pb) of different Me : V ratios were characterized with respect to phase composition, structure and valence state of vanadium sites as well as composition and acid-base properties of the surface using XRD, TEM, TPR, TPD/TPRS, FTIR, potentiometric titration, XPS, EPR, and UV/VIS-DRS. The latter two techniques were also applied in situ under catalytic reaction conditions. The following structure-reactivity relationships were derived by comparing the results of catalyst characterization with those of catalytic tests: Both V5+ and V4+ catalyze the ODH of propane; however, V4+ seems to be more selective though less active than V5+. V sites in octahedral or square pyramidal coordination are more active but less selective than VO4 tetrahedra. Isolated VO4 and V2O7 units as present in crystalline metal ortho-and pyrovanadates, respectively, are more selective but less active than VOx species in amorphous clusters or even in crystalline chain-or layer-like structures. The differences in the catalytic properties arising from different metal cations are governed not only by the oxidation potential of the latter but also to a major degree by the acid-base properties, the crystal size and the extent of structural disorder. Catalytic activity and selectivity of the Me-V-O catalysts decrease in the order Mg > Pb > Zn. The lower activity of Zn-V-O and Pb-V-O catalysts in comparison with Mg-V-O samples of similar composition is assumed to be due to large crystallites with low surface defect concentration. (C) 2001 Academic Press.
引用
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页码:45 / 58
页数:14
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