Supported reagents porosity

The impurities stick to the periphery of particle pores making the gas flow into the catalyst difficult or impossible. This in turn leads to a considerable increase in the diffusion resistances during the catalytic process. One way of fighting this phenomenon is to use double-porosity alumina. Micropores of about 20 nm are always useful to develop the specific surface area necessary for a good dispersion and stability of the catalytic phase. Macropores over 100 nm in diameter help to diffuse the reagents within the particles. However, the proportion of macropores must not be too great, as that would diminish the mechanical properties of the support correspondingly. For this reason, Rhone Poulenc has, since 1974, developed and marketed various exhaust, gas catalyst supports with specific surface areas of 2... 

In view of possible commercial applications of rice husk silicas, e.g. as catalyst supports, their surface areas and porosities are important properties. Nitrogen sorption measurements of the three differently treated rice husk silicas show that these are porous materials with moderately large surface areas. The surface areas are, in detail 73 m /g for the calcined material, 75 mVg in the case of the material oxidized by Fenton s reagent and 51 m /g for the rice husks treated with Caro s acid. As the shapes of the ad- and desorption isotherms reveal (Fig. 3), pores ranging from micro- up to macropores are present. 

---