Synthesis of 2,6-dichlorobenzonitrile from 2,6-dichlorotoluene by gas phase ammoxidation over VPO catalysts

Ammoxidation of 2,6-dichlorotoluene to 2,6-dichlorobenzonitrile is indeed an industrially important reaction for producing various commercially useful chemicals. In this contribution, differences in the catalytic performance of bulk, supported and promoted VPO samples are described. The choice of P/V ratio is found to play a key role on the catalytic properties of the catalysts. Activity is observed to decrease with increase in P/V ratio of the catalysts. About 55% yield of DCBN and ca. 95% conversion of DCT is obtained over bulk VPO solids having low P/V ratios (≤1). However, the catalytic performance of these bulk VPO solids is considerably improved when they are supported on γ-Al2O3 (Y-DCBN = 70% and X-DCT = >90%). In the direction of further enhancing the yield of DCBN, some selected transitional metal ions (Cr, Fe, Co and Mo) are also used as promoters for the present VPO solids. These promoted catalysts displayed superior performance compared to bulk and supported VPO catalysts. Amazingly, the yield of DCBN is significantly enhanced from 55% (on bulk VPO solids) to ca. 80% on the promoted VPOs, which is indeed a remarkable outcome of this study. This increase in the catalytic performance can be attributed to the surface enrichment of phosphorus in the supported and promoted catalysts compared to their corresponding bulk VPOs. Additionally, the influence of calcination temperature on the distribution of oxidation states of vanadium is presented.