A robust platinum carbonyl cluster anion [Pt3(CO)6]52- encapsulated in an ordered mesoporous channel of FSM-16:: FTIR/EXAFS/TEM characterization and catalytic performance in the hydrogenation of ethene and 1,3-butadiene

A robust trigonal prismatic cluster anion [Pt-3(CO)(6)](5)(2-)(v(CO) = 2078, 1878 cm(-1); lambda(max) = 405 and 702 nm; R-1(Pt-Pt) = 2.68 Angstrom (CN = 2.0); R-2(Pt-Pt) = 3.08 Angstrom (CN = 1.5)) is selectively synthesized in the ordered hexagonal channel of FSM-16 by the reductive carbonylation of H2PtCl6/NR4+/FSM-16 under a CO + H2O atmosphere at 323 K. The Pt cluster anion extracted in THF solution by cation metathesis was identified as [Pt-3(CO)(6)](5)(2-) by FTIR and UV-vis spectroscopic data. TEM observation showed that [Pb-3(CO)(6)](5)(2-) was uniformly dispersed and aligned in the mesoporous channels of FSM-16. The Pt-15 cluster anions formed in FSM-16 were relatively stabilized by the coimpregnated quaternary alkylammonium cations as NR4+ in the following order for the alkyl groups: butyl > ethyl > methyl, methyl viologen (MV) > hexyl >> no countercations. The EXAFS and FTIR studies demonstrated that [Pt-3(Co)(6)](5)(2-) in FSM-16 was transformed by the controlled removal of CO at 300-343 K into the partially decarbonylated Pt-15 cluster (R-1(Pt-Pt) 2.69 Angstrom, CN = 2.2; R-2(Pt-Pt) = 3.10 Angstrom, CN = 1.4). This sample showed IR spectra indicating a linear CO (v(CO) = 2062 cm(-1)) without a bridged one. The Pt carbonyl cluster was eventually converted by thermal evacuation exceeding 463 K to naked Pt particles (15 Angstrom diameter; R(Pt-Pt) = 2.76 Angstrom, CN = 7.8). The controlled removal of CO from [Pt-3(CO)(6-x)](5)(2-) in FSM-16 by thermal evacuation at 300-423 K yields samples with marked catalaytic activities for hydrogenation of ethene and 1,3-butadiene at 300 K. 1,3-Butadiene is selectively hydrogenated to l-butene on the partially decarbonylated Pt carbonyl clusters in FSM-16, whereas it is preferentially converted to n-butane on the naked Pt particles in FSM-16.