Effect of thermal treatment on the microstructure of sol–gel derived porous alumina modified platinum

Thin films of sol–gel derived Pt/alumina were prepared from a boehmite solution containing alumina-sec-butoxide and chloroplatinic acid. At 1100 °C, γ-Al2O3 phase was not present in the alumina sample but it remained in the Pt/alumina sample, suggesting that improved thermal stability of the γ-Al2O3 or the transition aluminas (γ-, δ- and θ-) was achieved. Except for samples thermally treated at 1000 °C, pore size distribution profiles of both, alumina and Pt/alumina composite thermally treated at 500–900 °C demonstrated a narrow pore size distribution. Alumina and Pt/alumina treated at 500 °C, 700 °C, 900 °C and 1100 °C, exhibited a type IV isotherm according to the BDDT classification, characteristic of mesoporous materials. Increasing the calcination temperature of the alumina sample from 500 °C to 700 °C increased the fractal dimension from 2.37 to 2.46. However, further increase from 900 °C to 1100 °C caused the surface fractal to decrease from 2.43 to 2.39, respectively.