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Fabrication and characterization of bimetallic Pt–Au nanowires supported on FSM-16 and their catalytic activities toward water–gas shift reaction

Mohamed, Mohamed Mokhtar, Khairou, K.S.
Journal of colloid and interface science 2011 v.354 no.1 pp. 100-108
Fourier transform infrared spectroscopy, absorbance, absorption, adsorption, alloys, atmospheric pressure, carbon dioxide, carbon monoxide, catalysts, catalytic activity, gases, gold, hydrogen, light, nanoparticles, nanowires, oxidation, platinum, porosity, surface plasmon resonance, surfaces, temperature, transmission electron microscopy, ultraviolet-visible spectroscopy, water
A facile, previously unexplored, method to synthesize bimetallic Pt–Au nanowires (20nm diameter×120–170nm long) on mesoporous FSM-16 (2.7nm) was fabricated by co-impregnation of H₂PtCl₆ with HAuCl₄ followed by evacuation at 300K and finally exposure to the CO/H₂O gas mixture (60:5Torr) at 323K for 1.0h. On the other hand, spherical monometallic nanoparticles of pure Pt (7.0nm diameter) and Au (7–26nm 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 323–373K. The optical absorption spectra showed a remarkable shift and broadening of Pt–Au surface Plasmon resonance band at 515nm 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 (2084cm⁻¹) and Pt–CO (1888cm⁻¹) 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, 2186cm⁻¹) along with a concomitant increase in the reduced gold (Au⁰–CO, 2124cm⁻¹) 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.