Silica modified with aluminum and its use as catalyst

Aluminium-or gallium modified silica or germania is prepared by reacting an aluminium (or gallium) derivative and a silicon (or germanium) derivative with a clathrating substance with the possible addition of a mineralising agent and an inorganic base, and crystallising the mixture thus obtained, so that a compound is formed which has the general formula: Si.(0.0012 - 0.0050)Al.Oy Ge.(0.0012 to 0.0050)Al.Oy Si.(0.0012 to 0.0050) Ga.Oy Ge.(0.0012 to 0.0050)Ga.Oy in which y is from 2.0018 to 2.0075. The modified silicas and the analogous compounds are efficient catalysts for a large number of reactions. A zeolite of formula (0.9+/-0.2)M2/n0.W2O3(5-100)YO2-2H2O in which M is H , NH4 , metallic cations or cations derived from amino alcohols, W is Al or Ga, Y is Si or Ge and z is 0-40 of ZSM-5 type is referred to as a modification.