New mineralization agents for the synthesis of MCM-41

Silicate and aluminosilicate MCM-41 molecular sieves have been synthesized in the presence of various new mineralization agents, such as methylamine, dimethylamine, ethylamine and diethylamine. The products were characterized with a series of techniques. XRD, TEM and nitrogen adsorption-desorption measurements suggest that the products possess highly ordered structures. Si-29 NMR results show that the resultant mesophase frameworks are condensed with a higher degree than those of products prepared with NaOH as the mineralization agent. These alkalimetal-free synthesis media offer a simple and effective method for the direct preparation of high quality H-type aluminosilicate MCM-41, as shown by XRD, Al-27 NMR and NH, TPD results. Both the pure silica and the aluminum-containing samples exhibit excellent thermal tin air up to 1373 K) and hydrothermal stability tin hot water of 353 K, 48 h for the former and 72 h for the later). The formation of the high quality MCM-41 material is discussed in terms of a buffer effect of the synthesis media, which is due to the presence of the new mineralization agents. The evidence was obtained by monitoring the pH values of the synthesis. (C) 1999 Elsevier Science B.V. All rights, reserved.