(143f) Study the Hydration Behavior of Surface Metal Oxide Species Via in-Situ Vibrational Spectroscopy

Authors: 
Wang, H., Rutgers University
Nguyen, T., Rutgers
Tsilomelekis, G., Rutgers, The State University of New Jersey
Water adsorption and its participation in heterogeneous catalytic reactions has been
studied theoretically and experimentally. In addition, the effect of water on the
molecular structure of surface dispersed metal oxide species has been underscored in
the open literature [1][2][3] . Recently, it was highlighted that in ethane activation, even
small amount of moisture favored dehydrogenation rather aromatization and could
enhance ethylene formation rate. [4] . Thus, a comprehensive study on interaction and/or
dissociation of water, an unavoidable product from oxidative dehydrogenation of
lower alkanes, with potential surface metal oxide active species as well as their
support is of topical character and could shed light on both reaction mechanism and
stability of active sites. Towards this direction, this work focuses on unravelling via
in-situ vibrational spectroscopy the sequence in which the hydration of dispersed
species occurs.
We couple Raman and DRIFT spectroscopy with in-line mass spectrometry to
understand surface hydration as a function of moisture content as well as temperature.
First, we study the dehydration process of supported metal oxides by means of an in-
situ Raman calcination approach. We observe a variety of anchored surface Mo and V
based species on TiO 2 that are temperature dependent. All these species appear to be
robust at each temperature in the absence of water. However, very small addition of
water vapors in the gas environment leads to significant structural changes which are
temperature as well as oxide dependent. During the hydration process, we observe
that both peak position as well as relative intensity (as compared to the pure support)
of the oxo-species (Me=O) varies significantly with both temperature and water
content in the gas phase. In addition, it is observed that the hydration induces larger
changes in the molybdenum based catalysts while vanadium dispersed species appear
to be more robust. The effect of the support (TiO 2 ) on the gradual changes of the oxo-
species will be also discussed in an effort to provide insights into the mechanism that
the hydration reaction occurs.
[1] Karim Hamraoui, Sylvain Cristol, Edmond Payen, and Jean-Franc¸ois Paul*
[2] Huaxiang Lin, Jinlin Long, Quan Gu, Wenxin Zhang, Rusheng Ruan, Zhaohui Li, Xuxu
Wang*
[3] Guido Busca, Helen Saussey, Odette Saur, Jean Claude Lavalley, Vincenzo Lorenzelli
[4] Mehdad. A, Catal. Sci. Technol., 2018, 8, 358-366