A facile, previously unexplored, method to synthesize bimetallic Pt–Au nanowires (20 nm diameter
120–170 nm long) on mesoporous FSM-16 (2.7 nm) was fabricated by co-impregnation of H2PtCl6
with HAuCl4 followed by evacuation at 300 K and finally exposure to the CO/H2O gas mixture (60:5 Torr)
at 323 K for 1.0 h. On the other hand, spherical monometallic nanoparticles of pure Pt (7.0 nm diameter)
and Au (7–26 nm diameter) were synthesized as well, by impregnation, at the same reaction conditions.
The catalysts were characterized by in situ FTIR spectroscopy, UV–vis absorption spectroscopy, TEM, TPR
and TPCOR. The catalytic activities toward the water–gas shift reaction (WGSR) were also examined
under atmospheric pressure and at the margin of 323–373 K. The optical absorption spectra showed a
remarkable shift and broadening of Pt–Au surface Plasmon resonance band at 515 nm apart from those
of individual analogue emphasizing bimetallic formation. Results from in situ FTIR spectroscopy indicated
that incorporation of Au assisted and stabilized the formation of carbonyl clusters of Pt–Au–CO
(2084 cm1) and Pt–CO (1888 cm1) inside the host FSM-16. The Pt–Au carbonyl clusters built up at
the moment of vanishing the linear carbonyl band of the charged Au (Au+–CO, 2186 cm1) along with
a concomitant increase in the reduced gold (Au0–CO, 2124 cm1) species. TPR profiles showed that the
H2 consumed was higher for Pt/FSM-16 than for Pt–Au/FSM-16 verifying the facile reduction of Pt moieties
after addition of Au. The CO adsorption peak maximum, in TPCOR, for Pt/FSM-16 occurred at higher
temperature than that of Pt–Au/FSM-16, which exhibited higher amounts of CO2 produced. The relative
decrease in CO bindings on bimetallic surface was responsible for increasing the CO oxidation activity
mainly through an association mechanism. Accordingly, the activity of Pt–Au/FSM-16 towards WGS
showed a marked increase (8–23 times) compared with those of monometallics emphasizing the dependence
of this reaction on the electronic defects of the nanowires. A straightforward reduction mechanism
was deduced for Pt–Au alloy formation in view of the results obtained. |
