Effects of Brønsted acidity in the mechanism of selective oxidation of propane to acetone on CaY zeolite at room temperature

The importance of Brønsted acid sites for partial oxidation of propane to acetone in CaY was investigated by in situ FTIR spectroscopy. With an increasing number of protons in Ca-Y, Volcano plots were observed for (1) amount of adsorbed propane; (2) initial acetone formation rate; (3) total amount of acetone after 20 h of reaction; (4) acetone selectivity. The results clearly show that Brønsted acidity increases the isopropylhydroperoxide (IHP) formation rate, most likely via a catalytic H+ transfer, and IHP decomposition into acetone and water. Moreover, with increasing IHP concentration 2-propanol was found in addition to acetone. Since an increasing number of Brønsted acid sites implies a decreasing number of Ca2+ in the zeolite, an optimal H+/Ca2+ ratio was observed for both activity and selectivity for acetone.