Relations between the catalyst structure, acid and catalytic properties of two types of silica (silica gel and layer silica) modified by gamma-ferric oxide nanoparticles of a different size (2-4 and 8-10 nm) were studied in the benzene alkylation by benzyl chloride. The catalysts were characterized by means of Mossbauer spectroscopy, temperature programmed NH(3) desorption and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) using CO and CD(3)CN as test molecules. It was found that the particle size and the silica structure strongly affect the catalytic behavior. (C) 2009 Elsevier B.V. All rights reserved.