Studies of acid properties of FeSiMCM-41 and LaSiMcM-41 by NH3-microcalorimetric and NH3-TPD measurements

The acidity of mesoporous materials FeSiMCM-41, LaSiMCM-41, SiMCM-41, AlSiM CM-41 and HAlSiMCM-41 has been investigated by microcalorimetric studies of the adsorption of ammonia and temperature programmed ammonia desorption me thod. In the initial stage, the acid strength sequence is SiMCM-41>HAlSiMCM -41>AlSiMCM-41>FeSiMCM-41>LaSiMCM-41, in agreement with that found for micr oporous molecular sieves materials. A small number of strong acid sites of SiMCM-41 may result from the aluminum impurity contained in the silica sour ce material. The acid density sequence is HAlSiMCM-41>AlSiMCM-41>FeSiMCM-41 >LaSiMCM-41 greater than or equal to SiMCM-41 and can be explained by the s tudies of existing states of trivalent atoms in these samples reported in p revious work. Since some NH3-TPD plots of these samples show the profiles t hat could not be back to baseline at elevated temperature, the technique of microcalorimetric adsorption is preferable in studying these samples.