Characterization of a novel solid catalyst, H3PO4/MoO3/SiO2, and its application in toluene nitration

A new catalyst, H3PO4/MoO3/SiO2, was prepared by modification of MoO3/SiO2 using phosphoric acid. The characterization of the catalyst was performed using scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and Raman and Infrared Spectroscopy. Molybdenum oxides in two polymorph forms (alpha and beta) were identified along with phosphomolybdic acid, polymolybdates and polyphosphates in various combinations on the modified surface. The suitability of the catalysts was examined for toluene nitration in the presence of fuming nitric acid. The catalysts were very effective in toluene nitration and the selectivity and toluene conversion depend on the nature of species present on the surface. Since the catalysts have significantly reduced activity in subsequent reactions, a simple process of regeneration was found. The MoO3/SiO2 modification with H3PO4 causes new domains on the surface to be obtained and increases catalytic properties in comparison to unmodified MoO3/SiO2 system. (C) 2011 Elsevier B.V. All rights reserved.