H-ZSM-5 adsorbs water solely through the formation of
hydrogen bonds. When only one H2O molecule is involved,
the O atom of H2O hydrogen bonds to the proton of the
Brønsted-acid site in the zeolite and one of the two H atoms of
H2O forms a hydrogen bond with an O atom in the zeolite
framework. Introduction of a second H2O molecule results in
the formation of one hydrogen bond between an H atom of the
first H2O molecule and the O atom of the second H2O molecule
and the formation of a second hydrogen bond between one of
the H atoms of the second H2O molecule and an O atom in the
zeolite framework. No evidence of proton transfer is observed
when either one or two molecules of H2O are adsorbed on
H-ZSM-5.