Catalyst precursor synthesis
Al2O3 (CATAPAL A – PP1688) was used as a support for -Mo2C.
MoO3/Al2O3 samples were prepared prior to -Mo2C/Al2O3 synthesis
with a nominal content of 20 wt.% MoO3 using the incipient
wetness impregnation method. Briefly, the methodology consisted
of dissolving the molybdenum salt (ammonium heptamolybdate
(NH4)6Mo7O24
•4H2O from Merck) in the smallest possible volume
of water (∼2 mL) to obtain the desired MoO3 content after the calcination
step. The heptamolybdate solution was dripped onto the
-Al2O3 substrate and to avoid slurry formation, intermediate heating
for 30 min at 393 K was done after addition of ca. 0.5 mL in order
to remove the excess of moisture. This process was performed until
all of the solution had been applied, and the material was left to dry
completely in a furnace kept at 393 K overnight. After this step, the
sample was calcined at 773 K for 3 h.
ˇ-Mo2C/Al2O3 synthesis
The 20 wt.% MoO3/Al2O3 sample was carburized using the
temperature-programmed carburization (TPC) methodology [28]
to obtain molybdenum carbide (-Mo2C/Al2O3). The oxide precursor
(∼0.600 g) had previously been weighed and placed in a quartz
U-shaped micro reactor, which was heated at a rate of 2.5 K min−1
under a stream of a 20% (v/v) CH4/H2 gas mixture (Lynde, 99.999%,
143 mL min−1) from room temperature up to 923 K. Once this final
temperature was attained it was kept constant over a period of 2 h.
Then the gas flowing through out the reactor was switched from
the 20% (v/v) CH4/H4 to pure He (Lynde, 99.999%) and the system
was allowed to cool down to room temperature