ON THE NATURE OF WATER BOUND TO A SOLID ACID CATALYST

The nature of the species formed when water interacts with Bronsted ac id sites in a microporous solid acid catalyst, HSAPO-34, was studied b y powder neutron diffraction and infrared spectroscopy. Previous infra red and computational studies had failed to unambiguously establish wh ether water is protonated to form hydronium (H3O+) ions or is merely h ydrogen-bonded to acid sites inside the zeolite. Our experiments clear ly showed that both species are present: An H3O+ ion is found in the e ight-ring channel of the zeolite and a second water molecule is hydrog en-bonded to an acid site on the six-ring.