Masaru Ichikawa

Catalytic hydroformylation of olefins over the rhodium, bimetallic RhCo, and cobalt carbonyl clusters supported with some metal oxides

Vapor-phase hydroformylation of ethylene and propene proceeded under atmospheric pressure at 25 to 180°C over the Rh and Co carbonyl clusters such as Rh 4 (CO) 12 , Rh 6 (CO) 16 , Rh 2 Co 2 (CO) 12 , RhCo 3 (CO) 12 , and Co 4 (CO) 12 supported with some specific metal oxides such as ZnO and MgO. It was suggested that the supported carbonyl clusters catalyzed the hydroformylation reactions when they were partially decarbonylated by subjecting to heat treatment in vacuo or under hydroformylation atmosphere. The activities and linear-isomer selectivities of aldehyde formation depend not only on the kinds of precursor carbonyl clusters but also on the metal oxides as supporting carriers: The specific activity order at 158°C for Rh carbonyl clusters supported on ZnO was Rh 4 (CO) 12 > Rh 6 (CO) 16 > Rh 7 (CO) 16 3NEt 4 > Rh 13 (CO) 23 H 2–3 2NBu 4 with a total range of ∼10. In contrast, the catalysts prepared from Rh(CO) 2 Cp, Rh 2 (CO) 3 Cp 2 , and RhCl 3 impregnated on ZnO showed negligible or small conversions in the reactions under similar conditions. The Rh carbonyl clusters were possibly stabilized with the basic oxides such as ZnO, MgO, TiO 2 , and La 2 O 3 , exhibiting higher hydroformylation activities. On the other hand, the hydroformylation reactions negligibly proceeded over the carbonyl clusters dispersed on acidic oxides such as alumina, silica-alumina, and V 2 O 5 . The bimetallic Rh Co cluster-derived catalysts exhibited higher selectivity of normal-isomer aldehyde, suggesting that Co atoms in the supported bimetallic Rh Co clusters behave as electronic “donor-ligand” to promote normal-intermediate on top of rhodium atom active for olefin hydroformylation reactions.

Template synthesis of nanoparticle arrays of gold, platinum and palladium in mesoporous silica films and powders

Mesoporous silica films were prepared on glass plates by a dip coating method, and the film/plate samples were used as a support for Au, Pt and Pd nanoparticles. By H2- or photo-reduction of metal precursors impregnated on the films, metal nanoparticles are formed with an ordered array structure in the mesopores. The nanoparticles are isolated by dissolving the silica film with a dilute HF solution, and the particles are stabilized with ligands such as 1-dodecanethiol and triphenylphosphine. The diameter of the separated nanoparticles is 2.5 nm with narrow distributions, showing that uniform particles are formed in the mesopores. Selective formation of metal nanoparticles rather than nanowires suggests that a 3D-hexagonal structure is involved in the 2D-hexagonal mesoporous silica films. To study the formation of nanoparticles in a 3D-hexagonal structure, HMM-2 powder was used as a support, and in fact Au and Pt nanoparticles are formed in the HMM-2 powders. The XRD study suggests that the Au nanoparticles in the film/plate have an anisotropic orientation in the mesoporous channels. The Au/film/plate sample gives a weak plasmon peak at 570–580 nm using diffuse-reflectance UV-visible spectroscopy, which is shifted to high wavelength by 50–60 nm compared with larger Au particles.

Selective hydrodechlorination of CFC-113 on Bi- and Tl-modified palladium catalysts

Abstract More than 80% selectivity in the hydrodechlorination of 1,1,2-trichlorotrifluoroethane (CFC-113) has been observed over palladium catalysts containing selected metal additives such as Ag, Bi, Cd, Cu, Hg, In, Pb, Sn, Tl to chlorotrifluoroethene (3FCl) and trifluoroethene (3FH). In particular, a bismuth modified palladium catalyst supported on SiO 2 and a thallium modified catalyst on active carbon provided 3FH and 3FC1 with more than 90% yield at 520-600 K. Kinetic studies suggest that the reaction route is CFC-113→ 3FC1→ 3FH and that the role of the metal additives is to suppress the hydrodechlorination of 3FC1 to 3FH or further hydrogenation of 3FH. The thermodynamic estimations imply that the modifier plays another role in the inhibition of hydrodefluorination. The IR studies of carbon monoxide chemisorption on the modified palladium catalysts show that the addition of bismuth or thallium leads to a drastic suppression of bridged carbon monoxide on palladium and to the enhancement of linear carbon monoxide. This shift indicates that the addition of the promoter results in the breaking the ensembles of palladium atoms. Further evidence for this mechanism comes from the temperature-programmed reduction spectra, where a reduction peak shifts to higher temperature. X-ray diffraction spectra, where a broad peak based on palladium shifted to low angle of 2θ by the addition of thallium, indicates the formation of Tl-Pd alloy or intermetallic compound.

Catalytic dehydrocondensation of methane towards benzene and naphthalene on transition metal supported zeolite catalysts: templating role of zeolite micropores and characterization of active metallic sites

The catalytic dehydrocondensation of methane to benzene and naphthalene with a bulky of hydrogen on transition metal supported zeolite catalysts is one of strategies for the catalytic conversion of methane and a challenging topic in heterogeneous catalysis. This paper is dealt with the current progress in catalytic dehydrocondensation of methane towards benzene and naphthalene on transition metal supported zeolite catalysts, in terms of templating role of zeolite micropores and metallic sites on Mo and Re supported zeolite catalysts. The effect of zeolite supports and active metallic phases in conjunction with the reaction conditions are discussed. The results of investigation on the carbonaceous deposits and the synergetic effect between the transition metal components and the zeolite supports, as well as, the active species and reaction mechanisms are revealed by the TPO/XPS/FT-IR/EXAFS and solid NMR studies.

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

Abstract The robust trigonal prismatic Pt 18 and Pt 15 cluster anions are selectively synthesized via [Pt(CO)Cl 3 ] − in FSM-16 (4.7 nm) and cis -Pt(CO) 2 Cl 2 in FSM-16 (2.8 nm) by the reductive carbonylation of H 2 PtCl 6 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 ] 6 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) ( ν CO =2078, 1880 cm −1 ) and [Pt 3 (CO) 6 ] 6 2− /FSM-16 (4.7 nm) ( ν 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 A) characteristic of a linear CO band ( ν 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 A (Pt–Pt C.N.=6.7, R =2.72 A) in FSM-16 (2.8 nm) and of 15 A (C.N.=7.9, R =2.74 A) in FSM-16 (4.7 nm). On the other hand, the platinum nanowires [2 and 4 nm (diameter)×50–500 nm (long)] are prepared using the cylindrical mesoporous channels of FSM-16 (2.8 and 4.7 nm) in the templating reduction of H 2 PtCl 6 by the exposure to γ-ray or UV-light ( λ 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 nm), whereas the average lengths of Pt wires are varied by the function of the Pt loading mass and time exposure to γ-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 A. 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.

Catalysis by supported metal crystallites prepared from metal carbonyl clusters: III. Catalytic vapor-phase hydroformylation of olefins over Rh, bimetallic RhCo, and Co crystallites prepared from the carbonyl cluster compounds dispersed on zinc oxide

The carbonyl clusters Rh/sub 4/(CO)/sub 12/, Rh/sub 6/(CO)/sub 16/, RhCo/sub 2/(CO)/sub 12/, RhCo/sub 3/(CO)/sub 12/, and Co/sub 4/(CO)/sub 12/ were deposited on ZnO and activated by pyrolysis (vacuum, 130/sup 0/-145/sup 0/C) or by activation above 90/sup 0/C in ethylene (or propylene), hydrogen, and carbon monoxide mixtures. The method of activation had no effect on the hydroformylation activity or selectivity. The specific rate for hydroformylation of ethylene or propylene to propanol and butyraldehyde, respectively, was 1.5-2.8 times higher on the rhodium derived from Rh/sub 4/(CO)/sub 12/ than on the rhodium derived from Rh/sub 6/(CO)/sub 16/, but the selectivity for the normal aldehyde isomer was higher on the latter catalyst. Relative rates for propylene hydroformylation depended on the catalyst precursor as follows: 100 for Rh/sub 4/(CO)/sub 12/, 60 for Rh/sub 2/Co/sub 2/(CO)/sub 12/, 42 for RhCO/sub 3/(CO)/sub 12/, and 5.2 for Co/sub 4/(CO)/sub 12/. IR spectroscopy suggested that the active species is a rhodium cluster carbonyl formed in situ from the metal crystallites formed upon activation; the role of cobalt in the bimetallic crystallites is apparently to act as electron donor to rhodium.

Preparation and catalysis of Pt and Rh nanowires and particles in FSM-16

Pt and Rh nanowires and/or particles were prepared in mesopores of FSM-16, and their characterization and catalytic performances were investigated. Irradiation of UV–Vis light to FSM-16 (pore size 2.7 nm) impregnated with H2PtCl6 in the presence of water and 2-propanol (or methanol) vapors led to the formation of Pt nanowires (diameter 2.5 nm, length 50–300 nm) in the mesopores of FSM-16. In contrast, H2-reduction of H2PtCl6/FSM-16 at 673 K for 2 h resulted in the formation of Pt nanoparticles in FSM-16. The XANES and XPS studies show that the Pt wires and particles are slightly electron-deficient, implying the interaction with the internal surface of mesopore. At the initial stage of the formation of Pt wires, it is found that small Pt nanoparticles are formed in the mesopores. Then Pt ions migrate and are reduced on the surface of the small particles, thus resulting in the formation of the Pt nanowires. Rh nanoparticles were prepared in FSM-16 by calcination of RhCl3/FSM-16 at 673 K and subsequent H2-reduction at 473 K. Furthermore, nanowires (diameter 2.5 nm, length 10–50 nm) were formed in FSM-16 by the similar photoreduction of the FSM-16 co-impregnated with H2PtCl6 and RhCl3. In hydrogenolysis of butane, Pt nanowire/FSM-16 exhibits higher catalytic activities than Pt nanoparticle/FSM-16, while Pt–Rh nanowire/FSM-16 shows high activity of isomerization to isobutane.

Bimetallic promotion of alcohol production in CO hydrogenation and olefin hydroformylation on RhFe, PtFe, PdFe, and IrFe cluster-derived catalysts

Iron-containing bimetallic catalysts were prepared from carbonyl clusters as precursors deposited on SiO2. FeRh4 and Fe2Rh4 cluster-derived catalysts showed high activity and selectivity for formation of ethanol and methanol in CO hydrogenation. Fe3Pt3, Fe6Pd6 and FeIr4 cluster catalysts gave methanol in high selectivity, while Fe-rich Fe4Pt and Fe4Pd were not selective catalysts. The RhFe cluster catalysts showed improved activity in hydroformylation of olefins; C4-alcohols were substantially obtained from C3 + CO + H2. Mossbauer and EXAFS studies on the Fe2Rh4/SiO2 catalyst show that highly dispersed RhFe bimetallic particles are located on the SiO2 surface, where Fe atoms exist preferentially in the state of Fe3+ even after H2 reduction. FTIR spectra of CO chemisorbed on Fe2Rh4/SiO2 exhibit a low-frequency band possibly due to the G and O-bonded CO on Rh-Fe3+ sites. Bimetallic promotion of alcohol production in CO hydrogenation and olefin hydroformylation is proposed to originate from the two-site interaction of Rh-Fe3+ (or Pt-Fe3+, Pd-Fe3+, IrFe3+) sites with CO to enhance migratory CO insertion.

Metal—support interaction of Rh4 Rb13 carbonyl clusters impregnated on Ti- and Zr-oxide-containing silica and their catalytic activities in the conversion of COH2 to ethanol

Rh4  Rh13 carbonyl clusters were impregnated onto Zr- and Ti-oxide-containing silica to provide highly dispersed Rh catalysts with a strong metal—support interaction, and exhibiting high activities for ethanol production in an atmospheric pressure COH2 reaction. The in situ i.r. and x.p.s. studies suggested that the precursor clusters such as Rh6(CO)2−15, Rh7(CO)3−16 and Rh13(CO)23Hn−5−n (n = 2 or 3) had reacted with surface OH (the acid sites of Ti- and Zr-oxide-containing silica) to form hydrido carbonyl clusters such as Rh6(CO)15H− and Rh13(CO)23H2−3. The apparent electronic states of the adsorbed carbonyl species and the reduced form formed from impregnated Rh4(CO)12, were studied by x.p.s. The behaviour of the adsorbed carbonyl species towards O2, NO and H2 is discussed. Some particular adsorbed cluster species were generated in the reaction of under a controlled atmosphere of CO and H2O, the i.r. bands of which resembled those of the original carbonyl clusters used. The kinetic experimental results revealed that ZrO2 and TiO2 on silica prevented Rh aggregation, and play a multifunctional modifying role with Rh to enhance CO dissociation and improve the selectivity for ethanol formation in the reaction of COH2 over the resulting catalysts.

XPS and TPD characterization of manganese-substituted iron-potassium oxide catalysts which are selective for dehydrogenation of ethylbenzene into styrene

Abstract Manganese-substituted (0–100%) iron–potassium oxide (Mn–Fe–K) catalysts which are selective for dehydrogenation of ethylbenzene to styrene were prepared by the alcoxide sol–gel method. They have been characterized by XPS, BET surface area measurement and TPD studies. The differences of surface properties between the Mn–Fe–K catalysts and unsubstituted iron–potassium oxide (Fe–K) catalyst were reasonably reflected in the XPS spectrum of oxygen (O 1s) and potassium (K 2p). The XPS spectra of Mn–Fe–K catalysts based on the binding energy shifts of O 1s and K 2p bands resembled those of KFeO2 as an active phase for the dehydrogenation of ethylbenzene. On the contrary, the unsubstituted Fe–K catalyst showed the XPS spectra including KOH and Fe3O4 as inactive phases. The presence of Mn ions in the catalyst matrix (γ-Fe2O3, MnFe2O4) results in stabilization of the KFeO2 active phase, and did not affect catalytic behavior of the K-promoted iron based oxide. The maximum enhancement of catalytic activity at the optimum 20% Mn-substitution is owing to the large surface area, the minimization of carbonaceous deposition, and the retardation of pyrolysis of KFeO2 to KOH and Fe3O4.