The catalytic behavior in butadiene and n-butane oxidn. of molybdovanadophosphoric acids with vanadium localized inside the primary (oxoanion) and/or the secondary structure is reported. The samples are characterized by IR, 31P-NMR, 51V-NMR, and UV-visible diffuse reflectance spectroscopies in order to obtain information on the nature and localization of vanadium in the samples before reaction and the possible changes occurring during the course of the catalytic reaction. Vanadium localized initially in the secondary structure can exchange with the molybdenum atoms of the oxoanion during the catalytic reaction. Introduction of vanadium in the molybdophosphoric acid structure enhances the selective formation of maleic anhydride from butadiene when vanadium is present both inside the oxoanion or localized in the secondary structure (before the catalytic tests), but the max. in catalytic performance is found for different amts. of vanadium, depending on where the vanadium is localized initially. However, when present in the secondary structure, vanadium also has a neg. influence on the activity of the heteropoly acid. On the contrary, in n-butane oxidn., the presence of vanadium enhances the rate of alkane activation due to the different rate-detg. step. The presence of V ions also affects the max. selectivity and yield to maleic anhydride from butane. V ions in the secondary structure are more selective at low conversion, while V ions inside the oxoanion are more selective at higher conversions and thus allow better max. yields to maleic anhydride. [on SciFinder(R)]
Reactivity of molybdovanadophosphoric acids: influence of the presence of vanadium in the primary and secondary structure
CENTI, Gabriele;
1993-01-01
Abstract
The catalytic behavior in butadiene and n-butane oxidn. of molybdovanadophosphoric acids with vanadium localized inside the primary (oxoanion) and/or the secondary structure is reported. The samples are characterized by IR, 31P-NMR, 51V-NMR, and UV-visible diffuse reflectance spectroscopies in order to obtain information on the nature and localization of vanadium in the samples before reaction and the possible changes occurring during the course of the catalytic reaction. Vanadium localized initially in the secondary structure can exchange with the molybdenum atoms of the oxoanion during the catalytic reaction. Introduction of vanadium in the molybdophosphoric acid structure enhances the selective formation of maleic anhydride from butadiene when vanadium is present both inside the oxoanion or localized in the secondary structure (before the catalytic tests), but the max. in catalytic performance is found for different amts. of vanadium, depending on where the vanadium is localized initially. However, when present in the secondary structure, vanadium also has a neg. influence on the activity of the heteropoly acid. On the contrary, in n-butane oxidn., the presence of vanadium enhances the rate of alkane activation due to the different rate-detg. step. The presence of V ions also affects the max. selectivity and yield to maleic anhydride from butane. V ions in the secondary structure are more selective at low conversion, while V ions inside the oxoanion are more selective at higher conversions and thus allow better max. yields to maleic anhydride. [on SciFinder(R)]Pubblicazioni consigliate
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