IRREVERSIBLE CHANGE OF PORE STRUCTURE OF MCM-41 UPON HYDRATION AT ROOM-TEMPERATURE

The pore structure stability of MCM-41 materials upon hydration/dehydr ation was studied by XRD, Si-29 MAS NMR, and gravimetric adsorption te chniques. Results demonstrated that collapses of the pore structure of MCM-41 occurred upon rehydration at room temperature due to the hydro lysis of the bare Si-O-Si(Al) bonds in the presence of water vapor. Fu ll structure collapses of MCM-41 were found to occur when a MCM-41 sam ple was left in air for three months. It is also suggested that care m ust be taken when XRD is used to evaluate the structure property of MC M-41 materials to avoid the possible adverse effects of water vapor.