The nitration of toluene has been studied in the vapor phase at various temperatures over a series of surface modified and unmodified ZSM-5 (Si/Al = 170) loaded with H3PO4, differing in the external surface treatment of the zeolites. All samples were characterized by X-ray diffraction, BET and FT-IR. The nature of acid sites of the supports, i.e., H3PO4/ZSM-5-surf-170 and H3PO4/ZSM-5-170 was determined using FT-IR-pyridine adsorption Study. 2,4,6-Trimethyl pyridine adsorption was used for calculating the external surface acidity of the H3PO4/ZSM-5-surf-170 and H3PO4/ZSM-5-170. The superior performance of the externally blocked catalysts (modified) relevant to the H3PO4/ZSM-5-170 catalyst shows that by blocking the external surface area of the ZSM-5 support, it exhibits a superior catalytic selectivity than the unmodified catalyst. Catalysts containing 0-4.9 wt.% P were prepared using ZSM-5-surf-170 and ZSM-5-170, and their catalytic performance was determined for the vapor phase nitration of toluene to 4-nitrotoluene (4-NT), 2-nitrotoluene (2-NT) and oxidation products. The effect of reaction temperature, H3PO4 content, feed ratio of toluene to HNO3. WHSV, TOS and carrier gas flow rate was also investigated. (C) 2008 Elsevier B.V. All rights reserved.