Hydrothermal synthesis of molybdenum oxide catalyst: Heteropoly acids encaged in US-Y

Molybdenum oxide was encaged into the supercages of US-Y by using a hydrothermal synthesis technique. Silicomolybdic acid (SMA), and phosphomolybdic acid (PMA), heteropoly acids (HPAs) with a Keggin structure, were synthesized by refluxing treatments with phosphoric or nitric acids. FT-IR, and EXAFS analyses revealed the presence of HPAs even after washing several times in hot water, indicating that the HPA molecules were anchored in the supercages. In addition, not only PMA but also SMA were detected after the treatment with phosphoric acid, suggesting that the refluxing induced the reaction of Si species of US-Y. The catalytic activity of PMA encaged in US-Y demonstrated that both the dispersion of PMA and the presence of SMA acted synergistically as active sites for partial oxidation of methane.