This work describes a method to synthesize free-standing nanoplatinum wires (8-25 nm diameter and 30-100
nm length) fabricated by CO (200 Torr)/water (20 Torr) under a high-pressure Hg lamp at 300 K, for 36 h,
induced from H2PtCl6 impregnated with FSM-16 (2.7 nm). On the other hand, stabilized platinum nanoparticles
(spherical) grown by consecutive reductive carbonylation of a CO (200 Torr) and CO (20 Torr)/water (2
Torr) system at 323 K exhibited mean particle sizes of 2-10 nm. The structure, dispersion behavior, and
surface morphology of the materials have been characterized by temperature programmed surface reaction of
CO (TPSR), temperature programmed reduction (TPR), N2 sorpitometry, and transmission electron microscopy
techniques. The Pt nanowires showed a higher catalytic activity toward the water-gas shift reaction (WGSR)
than that of nanoparticles. It has been shown that the activity does not depend on the structural and
morphological characteristics of Pt/FSM-16 such as specific surface area or primary crystallites size but depends
on Pt geometry. Investigation of the surface intermediates observed by in situ Fourier transform infrared
spectroscopy formed over Pt nanowires and Pt nanoparticles during the WGSR depicted the developing of
unidentate formate species on the former and carbonates on the latter. TPSR demonstrated the facile interaction
of CO with nanowires (243-373 K) at lower temperatures, presumably dissociatively, than with nanoparticles
(243-493 K). The same result was accomplished using TPR, comprehending that complete reduction was
attained at 723 K for the former, but it did not reach completion until 873 K for the latter. This indicated that
cationic Pt plays a crucial role in catalyzing WGSR at 323 K. Other issues regarding the binding of CO on
Pt particles, declining activity with temperatures, and CO cluster bonds either on Pt nanoparticles or nanowires
were also discussed. |
