(439f) Pressure Dilution, a New Method to Prepare a Stable Ni/Fumed Silica Catalyst for the Dry Reforming of Methane to Produce Hydrogen

V. Danghyan, S. Calderon Novoa, A. Mukasyan and E. E.
Wolf

Department
of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame,
IN

One
of the main limitations of using the dry reforming of methane (DRM) on Ni
catalysts is its deactivation due to the carbon formation [1]. For SiO₂ supported Ni
catalysts, due to the weak metal-support interaction, Ni crystallites have high
degree of reduction that results in high initial activity, but also in
favorable conditions for carbon formation, eventually resulting in catalyst
deactivation [2]. The main objective of this work was to find the pathways
between C formation, catalyst structure, and catalyst deactivation with the aim
to develop catalysts with increased activity and stability. In this context, a novel method of catalyst preparation,
using pressure dilution, has developed, which increased the metal dispersion
and stability of Ni/fumed SiO₂ catalysts.

Catalysts prepared by impregnation of Ni(NO₃)₂·6H₂O
onto fumed SiO₂, were subjected to various pretreatments which
yielded high initial activities at 600^oC. The activation energy was
measured to be 91 kJ/mol and the initial rate was of
8.5 [mol of CH₄/ g_Ni
h]. Depending on the pretreatment, however, the catalysts deactivated at
different rates due to carbon formation. The carbon structure was studied by
SEM/TEM; is was found that carbon accumulates mostly in the form of carbon
nanotubes (C-NT) with Ni crystallites at the top, where the reaction takes
place without affecting the activity during first hours of TOS. There is also
formation of clumps of entangled C-NT with Ni crystallites encapsulated by the
entangled C-NT, leading to loss of active area and deactivation.

A newly discovered method of catalyst preparation,
referred as pressure dilution (fig. 1), resulted in a significant increase in
Ni dispersion from 19% to 61%, when supported on fumed SiO₂.
Moreover, it was found that Ni dispersion can be controlled by the pressure
applied during catalysts’ preparation.

Fig. 1     Illustration of catalyst preparation methods and their effect on
the metal dispersion and carbon formation during DRM.

The higher dispersion resulted in a higher catalyst
activity and increased stability towards carbon formation.  A hypothesis of the re-dispersion process
occurring during p-dilution is proposed.

References:

(1)   
M.C.J. Bradford, M.A Vannice,
Catal. Rev. 41:1 (1999), 1-42.

(2)   
J.W. Han, J.S. Park, M.S. Choi, H. Lee, Appl. Catal. B 203 (2017) 625-632.