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To study the effect of W concentration and activation temperature of the catalysts a series of WO x /ZrO 2 samples with varying concentration of W (10–25 wt.%) were prepared and activated at 650/750 °C. XRD of sample shows 15 wt.% W stabilizes the tetragonal phase of zirconia up to 750 °C. Above and less than 15 wt.% shows peaks corresponding to monoclinic WO 3 and monoclinic ZrO 2 , respectively. Further, the tungsten modification stabilizes the specific surface area of ZrO 2 . There is an increase in the surface area observed up to 15 wt.% W, which declines on further increase in the concentration. The NH 3 TPD confirms the presence of acid sites with varying strength from the broad desorption profile. The 15 wt.% W and activated at 750 °C shows maximum acidity. The results of the nitration reaction of chlorobezene imply the 15 wt.% W and activation at 750 °C shows maximum activity. Not only yield, a better para -selectivity is also achieved with WO x /ZrO 2 samples. Effect of activation temperature, W concentration and reaction parameters such as reaction temperature, reaction time, the presence of solvent and solvent free medium on activity and selectivity are studied in details. |
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