FT-IR data show that the alkyl-aromatics toluene, ortho-, meta- and para-xylene are activated by the surface of vanadia-titania catalysts in the form of benzyl species. Surface reaction pathways have been established upon heating with and without gas-phase oxygen, relevant with respect to the mechanisms of heterogeneously catalyzed oxidation and ammoxidation of alkylaromatics. Side-chain oxidation, giving aromatic aldehydes and carboxylic acids, as well as phthalic anhydride from o-xylene, involves successive reaction with the catalyst oxidized surface sites. On the contrary, ring oxidative breaking giving maleic and citraconic anhydrides involves reaction with gas-phase oxygen. Side-chain oxidation and ammoxidation routes are interplayed.
Selective and Nonselective Pathways In Oxidation and Ammoxidation of Methyl-aromatic Compounds Over Vanadia Titania Catalysts - Fourier-transform Infrared Spectroscopic Studies
BUSCA, GUIDO
1993-01-01
Abstract
FT-IR data show that the alkyl-aromatics toluene, ortho-, meta- and para-xylene are activated by the surface of vanadia-titania catalysts in the form of benzyl species. Surface reaction pathways have been established upon heating with and without gas-phase oxygen, relevant with respect to the mechanisms of heterogeneously catalyzed oxidation and ammoxidation of alkylaromatics. Side-chain oxidation, giving aromatic aldehydes and carboxylic acids, as well as phthalic anhydride from o-xylene, involves successive reaction with the catalyst oxidized surface sites. On the contrary, ring oxidative breaking giving maleic and citraconic anhydrides involves reaction with gas-phase oxygen. Side-chain oxidation and ammoxidation routes are interplayed.
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