An nanoparticles embedded within mesoporous silica particles have been prepared and used as catalysts for CO oxidation. The silane APTS (H2N(CH2)(3)-Si(OMe)(3)) was used to surface-functionalize mesoporous silica in a direct method. The functionalized mesoporous silica was used to absorb the gold precursor AuCl4- and gold nanoparticles were formed inside the nanochannels after chemical reduction. The catalysts were activated by calcinations, followed with hydrogen reduction at 600 degrees C. MCM-41, MCM-48 and SBA-15 were used as the supports to prepare An nanoparticles, resulting in different particle sizes of An. The catalysts are active in the oxidation of carbon monoxide, reaching activity values as high as 7.0 x 10(-3) mmol g(cat)(-1) S-1 at 353 K. The conversion of CO increases with decreasing size of gold Ca nanoparticles. (c) 2005 Elsevier B.V. All rights reserved.