Direct Synthesis of Dimethyl Ether on Bifunctional
Catalysts Based on Cu–ZnO(Al) and Supported H3PW12O40: Effect of Physical Mixing on Bifunctional
Interactions and Activity
posted on 2021-11-18, 13:33authored byElena Millán Ordóñez, Noelia Mota, Rut Guil-López, Barbara Garcia Pawelec, José Luis García Fierro, Rufino M. Navarro Yerga
We studied different preparation
methods to synthesize a series
of bifunctional hybrid catalytic systems for the direct synthesis
of DME from syngas. The objective was to optimize the contact and
interaction between the methanol synthesis catalyst and the methanol
dehydration catalyst (Cu/ZnO/Al2O3 and H3PW12O40 supported on TiO2, respectively) by using different mixing methods (simple mixing,
mixing–milling, suspension, and mixing–pressing). It
has been found that the close contact between methanol synthesis and
acidic functions is highly dependent on the degree of mixing of the
two catalysts. In this respect, the hybrid catalyst prepared by mixing–pressing,
which represents the closest contact, shows the strongest alterations
in both catalytic functions. These modifications are associated with
a decrease in copper surface area and a decrease in strong acid sites
caused by the physical blocking of active sites or by cation exchange
of the Cu2+/Zn2+ species from Cu–ZnO(Al)
and the H+ from the H3PW12O40 units. The activity results demonstrated that the mixing–pressing
method leading to a closer contact between the two catalytic functions
led to a very low dimethyl ether time yield compared to the other
bifunctional catalysts prepared by less severe mixing methods (19.4
vs 205–335 μmol/min·gcat). This work
clearly indicates the importance of the mixing method in the synthesis
of the hybrid catalyst to optimize the distance and interaction between
the metal and acid sites.