Propane selective oxidation on alkaline earth exchanged zeolite Y: room temperature in situIR study

Abstract

The effect of zeolite Y ion-exchanged with a series of alkaline-earth cations on selective propane oxidation at room temperature was studied with in situ infrared spectroscopy. Isopropylhydroperoxide was observed as a reaction intermediate and can be decomposed into acetone and water. Contrary to previous studies, BaY was found to be active at room temperature. The reaction rate increased in the order BaY < MgY < SrY < CaY based on the rate of formation of adsorbed acetone. Surprisingly, the acetone/water ratio was found to increase with cation size, while no other products could be detected. Moreover, the acetone/isopropylhydroperoxide ratio decreased with decreasing number of Brønsted acid sites. Both observations mark the importance of Brønsted acid sites for this reaction, in addition to alkali (earth) cations. A two-step mechanism with two different active sites is proposed. Conversion of propane into isopropylhydroperoxide takes place on cations, while the decomposition into acetone occurs by Brønsted acid sites.