THE EFFECTS OF PROCESSING PARAMETERS ON THE SYNTHESIS OF SILICEOUS MCM-41 FROM COLLOIDAL SILICAS

Well-ordered as-synthesized siliceous MCM-41 mesoporous molecular siev es can be prepared from the sol of colloidal silica (Ludox HS-40 and A S-40) only under optimized conditions. Two processing parameters have a significant effect on the structure. First, the period of stirring t he mixture of Ludox AS-40 or HS-40 and tetraethylammonium hydroxide sh ould be extended to 22 h. Second, the following temperature regime sho uld be used: the reaction mixture consisting of colloidal silica, tetr aethylammonium hydroxide, hexadecyltrimethylammonium chloride and wate r is being first aged at ambient temperature for 20 h, then the temper ature is gradually increased and finally the mixture is kept at 100 de grees C for 40 h. As-made MCM-41 prepared even by an optimized procedu re contains after calcination some proportion of an amorphous phase. E xtraction with water of the as-made material is a suitable procedure f or the improvement of the phase purity as less well-ordered and amorph ous particles are preferentially dissolved and thus removed. In this w ay, a substantial improvement in the quality of MCM-41 molecular sieve s can be achieved.