Generation of Bronsted acid sites on Si-MCM-41 by grafting of phosphorus species

Phosphorus species could be grafted onto the surface of Si-MCM-41 by simply treating Si-MCM-41 with phosphoric acid for a very short period, followed by high temperature calcination. The existence and state of surface phosphorus species grafted on Si-MCM-41 are confirmed by XPS measurement. Using XRD and N-2 adsorption measurements, the uniform mesoporous structure of MCM-41 is shown to be quite stable under phosphoric acid treatment. FTIR results show that the surface phosphorus species grafted onto the surface of MCM-41 can selectively increase the number of Bronsted acid sites on the surface without forming any Lewis acid sites. Using NH3-TPD, the mild acidity of the generated Bronsted acid sites on phosphorus-containing MCM-41 significantly enhances its catalytic activity for the dehydration of isopropanol.