Catalytically active silica and alumina gel and process for preparing it

Claim 1

Silica and alumina gel, which is amorphous at X-rays, has a molecular ratio of SiO 2 /Al 2 O 3 comprised within the range of from 30/1 to 500/1, a surface area comprised within the range of from 500 to 1000 m 2 /g, a total volume of pores comprised within the range of from 0.3 to 0.6 ml/g, an average diameter of the pores of the order of magnitude of 10 Å or less and is free, or substantially free, from pores having a diameter larger than 30 Å, obtained by: (a) preparing an aqueous solution of tetra-alkyl-ammonium hydroxide (TAA-OH) in which the alkyl is selected from among ethyl, n.-propyl and n.-butyl, of a soluble compound of aluminum capable of yielding Al 2 O 3 by hydrolysis and of a soluble silicon compound capable of yielding SiO 2 by hydrolysis; with the amount of the constituents of the solution being such as to comply with the following values of the following molar ratios: ______________________________________ SiO.sub.2 /Al.sub.2 O.sub.3 from 30:1 to 500:1; TAA--OH/SiO.sub.2 from 0.05:1 to 0.2:1; H.sub.2 O/SiO.sub.2 from 5:1 to 40:1; ______________________________________ (b) heating the so-obtained solution in order to cause the gelification to occur; (c) drying the obtained gel; and (d) calcining the dried gel, by operating first under an inert atmosphere and then under an oxidating atmosphere.