Generation of Brønsted 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 N2 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 Brønsted acid sites on the surface without forming any Lewis acid sites. Using NH3–TPD, the mild acidity of the generated Brønsted acid sites on phosphorus-containing MCM-41 significantly enhances its catalytic activity for the dehydration of isopropanol.