The modification of catalyst structures can be very important for achieving high activities, selectivities, and stabilities. Chemical vapor deposition (CVD) is one method that can be used for this purpose. In this work, SiO2 has been deposited on the external surface of Ni/Al2O3 catalysts using CVD in a fluidized bed and the deposition parameters (time and temperature) studied. The catalysts were characterized using N-2 physisorption, H-2 and CO chemisorption, NH3 temperature-programmed desorption, X-ray diffraction, and reactivity for n-octane hydrocracking. The pore openings of Ni/Al2O3 were narrowed such that H-2 (2.9 A) uptake remained essentially constant while N-2 (3.6 A) and CO (3.8 A) were excluded. As well as changing the pore structure, the deposited silica increased the Bronsted acidity of the Ni/Al2O3 catalysts. The n-octane conversion achieved over the coated catalysts was a balance between the number of strong acid sites and the accessibility to these sites.