Sintering of the porous supported metal catalysts

Abstract

The sintering of the porous supported metal catalysts has been studied through both the mathematical model and the experiments. The model is similar to that of Ruckenstein and Dadyburjor(8) ; it postulates the splitting of single metal atoms and multiatom particles from larger particles, their diffusion along the substrate and coalescence of particles that collide. Multimodal particle size distribution could be obtained from numerical results, and the pore size of the substrate was found to affect the rate of decrease of the exposed metal surface area. Pt/SiO$_2$ catalysts were prepared by ion exchange method, and sintered in hydrogen atmospheres at temperatures of 600, 700, and $800\,^\circ\!C$ respectively. Characterization of sintered catalysts was carried out by hydrogen chemisorption. The hydrogen adsorption measurements were carried out at room temperature after reduction and evacuation at $350\,^\circ\!C$. The results of hydrogen chemisorption were represented in terms of (H/Pt)/(H/Pt)$_o$, which could be substituted for D/D$_o$. The rate of sintering was found to be slower for small initial dispersion but after sufficiently long time the total exposed surface area of metal approached the same value. The treatments in hydrogen resulted in monotonic decrease of metal surface area with increasing sintering temperature, and after long time the dispersion approached the stable value. The above results were discussed and compared partially and qualitatively with the numerical ones.