To study the effect of W concentration and activation temperature of the catalysts a series of WOx/ZrO2 samples with varying concentration of W (10-25 wt.%) were prepared and activated at 650/750 degrees C. XRD of sample shows 15 wt.% W stabilizes the tetragonal phase of zirconia up to 750 degrees C. Above and less than 15 wt.% shows peaks corresponding to monoclinic WO3 and monoclinic ZrO2, respectively. Further, the tungsten modification stabilizes the specific surface area of ZrO2. There is an increase in the surface area observed up to 15 wt.% W, which declines on further increase in the concentration. The NH3 TPD confirms the presence of acid sites with varying strength from the broad desorption profile. The 15 wt.% W and activated at 750 degrees C shows maximum acidity. The results of the nitration reaction of chlorobezene imply the 15 wt.% W and activation at 750 degrees C shows maximum activity. Not only yield, a better para-selectivity is also achieved with WOx/ZrO2 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. (c) 2006 Elsevier B.V. All rights reserved.