The specific surface area of the samples was determined from the adsorption–desorption isotherms of N2 at −196 °C using Chromatech (a Nova 2000 series apparatus) and applying BET equation. All samples were degassed under vacuum at 200 °C for 2 h prior to measurement. Particle size was determined by X-ray diffraction (XRD) analysis with a Bruker axis D8 instrument using Cu Kα radiation (λ=1.540 Å) at room temperature. The crystallite size of composite catalysts was calculated using the Scherrer Eq. (1).