Templating fabrication of platinum nanoparticles and nanowires using the confined mesoporous channels of FSM-16 - their structural characterization and catalytic performances in water gas shift reaction

The robust trigonal prismatic Pt-18 and Pt-15 cluster anions are selectively synthesized via [Pt(CO)Cl-3](-) in FSWI-16 (4.7 nm) and cis-Pt(CO)(2)Cl-2 in FSM-16 (2.8 nm) by the reductive carbonylation of H2PtCl6 in the confined mesoporous channels of FSM-16, respectively. The Pt cluster anions extracted from the resulting samples in the THF solution by cation metathesis with [PPN]Cl are identified as [Pt-3(CO)(6)](5)(2-) in FSM-16 (2.8 nm) and [Pt-3(CO)(6)](5)(2-) in FSM-16 (4.7 nm) by the FTIR and UV-Vis spectroscopic data. The EXAFS and FTIR studies demonstrated that [Pt-3(CO)(6)](5)(2-)/FSM-16 (2.8 nm) (nu(CO) = 2078, 1880 cm(-1)) and [Pt-3(CO)(6)](6)(2-)/FSM-16 (4.7 nm) (nu(CO) = 2056, 1879 cm(-1)) were transformed by heating at 300-343 K into the partially decarbonylated Pt clusters (Pt-Pt; C.N. = 7.6, R = 2.73 Angstrom) characteristic of a linear CO band (nu(CO) = 2015 cm(-1)). According to the EXAFS and TEM observation, Pt carbonyl clusters are eventually converted above 473 K to naked Pt particles of 11 Angstrom (Pt-Pt C.N. = 6.7, R = 2.72 Angstrom) in FSM-16 (2.8 MI) and of 15 Angstrom (C.N. = 7.9, R = 2.74 Angstrom) in FSM-16 (4.7 nn). On the other hand, the platinum nanowires [2 and 4 nm (diameter) x 50-500 nm (long)] are prepared using the cylindrical mesoporous channels of FSM-16 (2.8 and 4.7 Mn) in the templating reduction of H2PtCl6 by the exposure to gamma-ray or W-light (lambda(max) > 254 nm) under the atmosphere of 2-propanol and water. It was demonstrated by the TEM observation and EXAFS characterization that the diameters of Pt nanowires formed in FSM-16 are consistent with those of FSM-16 used (2.8 and 4.7 nn), whereas the average lengths of Pt wires are varied by the function of the Pt loading mass and time exposure to gamma-ray and UV-light. The observed electron beam diffraction patterns indicate that the Pt wires consist of a single crystal phase of Pt(110) having a lattice fringe of 2.27 Angstrom. It is of interest to find that the Pt nanowires in FSM-16 (2.8 nm and 4.7 nm) exhibited an unique IR spectrum in CO chemisorption and the remarkable activities per surface Pt atom (TOF) for water gas-shift reaction at 323-393 K by 60-90 times larger than those of Pt nanoparticles in FSM-16 and even conventional metal catalysts. (C) 1999 Elsevier Science B.V. All rights reserved.