1. Field of the Invention
This invention relates to a porous material composed of layered silica and metal oxide, and to a process for manufacturing the same. More particularly, it is concerned with a porous material composed of layered silica and metal oxide which is useful as an adsorbent, or catalyst for molecules having a high molecular weight, and which has a particularly high heat resistance.
2. Description of the Related Art
Zeolites are typical of the porous materials which are used as catalysts or adsorbents. Zeolites are widely used as adsorbents and catalysts, since they are composed of SiO.sub.2 and Al.sub.2 O.sub.3, and have numerous pores which are suitable for molecular adsorption, and possess the properties of solid acids which they owe to aluminum. It has, however, been impossible to use zeolites as adsorbents or catalysts for molecules having a high molecular weight, or bulky molecules, as their pores generally have diameters which are smaller than 10 .ANG., and do not, therefore, admit those molecules.
Pillared clays have been synthesized to improve the drawbacks of zeolites as hereinabove pointed out, as described in U.S. Pat. No. 4,216,188. The pillared clays have the structure of cross-linking of clays unit layers with metal oxides, and have a pore diameter of several tens of angstroms which is larger than that of zeolites. They have, therefore, the advantage of being useful as catalysts and adsorbents for molecules having a high molecular weight, or bulky molecules.
The pillared clays can, however, withstand a maximum temperature of only about 600.degree. C., since the clay minerals, such as smectite, contain "structure" water. If they are heated to a higher temperature, their pore structure is destroyed as a result of the loss of the structure water. They cannot, therefore, be used as catalysts for the catalytic cracking of petroleum, or for the purification of exhaust gas which are exposed to a temperature in the neighborhood of 800.degree. C.