Highly selective vapor phase nitration of toluene to 4-nitro toluene using modified and unmodified H3PO4/ZSM-5 Original Research Article

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.