The Kinetics of the Vapor-Phase Ammoxidation of Xylene Isomers over a Vanadium Catalyst

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Abstract
The kinetics of the vapor-phase ammoxidation of xylene isomers over a vanadium oxide catalyst was studied in a flow system. The reaction-rate data obtained for each xylene were then correlated with the rate equations based upon the Langmuir-Hinshelwood mechanism; this correlation suggested that each xylene reacted by a parallel consecutive reaction scheme in which tolunitrile was involved as an intermediate. The order of the relative ease of reaction was: para>meta\fallingdotseqortho. The ratio of the specific rate constant of xylenes, kx, to that of tolunitriles, kM, was 6 for meta and para isomers and 4 for the ortho isomer at 400°C; this ratio decreased with an increase in the reaction temperature. The order of relative ratios for the direct formation of dicyanobenzenes from xylenes was ortho>meta>para, while that for the direct formation of carbon oxides and hydrogen cyanide was ortho\fallingdotseqmeta>para. The ratio of the specific rate constant for the formation of dicyanobenzenes from tolunitriles, k2, to kM decreased with an increase in the ratio of kx to kM. These results seem to result from the adsorptivities of xylenes and tolunitriles on the catalyst surface.

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