Exfoliated graphene sheets decorated with metal / metal oxide nanoparticles: simple preparation from cation exchanged graphite oxide

We produced carbon hybrid materials of graphene sheets decorated with metal or metal oxide nanoparticles of gold, silver, copper, cobalt, or nickel from cation exchanged graphite oxide. Measurements using powder X-ray diffraction, transmission electron microscopy, and X-ray absorption spectra revealed that the Au and Ag in the materials (Au-Gr and Ag-Gr) existed on graphene sheets as metal nanoparticles, whereas Cu and Co in the materials (Cu-Gr and Co-Gr) existed as a metal oxide. Most Ni particles in Ni-Gr were metal, but the surfaces of large particles were partly oxidized, producing a core-shell structure. The Ag-Gr sample showed a catalytic activity for the oxygen reduction reaction in 1.0 M KOH aq. under an oxygen atmosphere. Ag-Gr is superior as a cathode in alkaline fuel cells, which should not be disturbed by the methanol cross-over problem from the anode. We established an effective approach to prepare a series of graphene-nanoparticle composite materials using heat treatment

CO oxidation on perovskite-type LaCoO3 synthesized using ethylene glycol and citric acid

In order to synthesize perovskite-type LaCoO3 with good surface crystallinity, the gel prepared by adding both ethylene glycol (EG) and citric acid (CA) to the aqueous solution of La(NO3)3 center dot 6H(2)O and Co(NO3)(2) center dot 6H(2)O was fired at 600 degrees C in air for 3 h. The transmission electron microscopy (TEM) observation indicated that the particles of LaCoO3 tended to have a uniform shape at EG/CA = 4. Although, the specific surface area of LaCoO3 synthesized using both EG and CA was slightly smaller than that of LaCoO3 synthesized using only CA, the catalytic activity of CO oxidation became higher by adding EG

Effect of Pore Size and Nickel Content of Ni-MCM-41 on Catalytic Activity for Ethene Dimerization and Local Structures of Nickel Ions

The catalytic activity of nickel ion-loaded mesoporous silica MCM-41 (Ni-M41) for ethene dimerization was investigated as a function of the pore size and the amount of nickel. In addition, the silica wall and the loading of the nickel species were characterized. The Ni-M41 samples with smaller pore size and higher Si/Ni ratio exhibited greater reaction rate constants. The Fourier transform infrared (FT-IR) spectra indicated the formation of 2:1 nickel phyllosilicate-like species along the pore wall. Furthermore, the IR band at approximately 570 cm^–1 and the X-ray absorption fine structure (XAFS) spectra indicated the existence of five-membered rings consisting of Si–O on the M41 pore wall in addition to the typical six-membered ones. On the basis of the UV–vis–NIR diffuse reflectance (UV–vis–NIR DR), FT-IR, and XAFS data, we propose that the three- and four-coordinated Ni²⁺ ions lie on the five- and six-membered Si–O rings of silica, respectively. Nitrogen monoxide was employed as a probe molecule in the FT-IR and UV–vis–NIR DR experiments and revealed that NO adsorbed as di- and mononitrosyl species on the three- and four-coordinated Ni²⁺ ions. The intensity of the dinitrosyl species on the three-coordinated Ni²⁺ ions correlated with the catalytic activity for ethene dimerization. Therefore, the three-coordinated Ni²⁺ ions are proposed to act as the active site for the reaction

Dual-Copper Catalytic Site Formed in CuMFI Zeolite Makes Effective Activation of Ethane Possible Even at Room Temperature

The role of dual-cation sites in zeolites has received a renaissance in chemistry and industry directed toward fixation and activation of various gases; such sites may be expected to be more efficient than a single-cation site. We aimed to clarify the real active centers in the copper-ion-exchanged MFI-type zeolite (CuMFI) for ethane (C₂H₆). A peculiar feature was found in the appearance of the characteristic IR bands at 2644 and 2582 cm^–1 when C₂H₆ was adsorbed on Cu⁺ formed in CuMFI. The existence of dual species composed of two Cu⁺ ions bridging C₂H₆ was clearly indicated by extended X-ray absorption fine structure (EXAFS) data. Density functional theory calculations gave clear evidence that the two IR bands are distinctly due to C₂H₆ adsorbed on the dual-Cu⁺ site and not on a single site; this agrees with the EXAFS data. These data lead us to conclude that the dual-Cu⁺ site in the CuMFI sample is indispensable for efficient activation of C₂H₆ through the simultaneous interaction of C₂H₆ with two Cu⁺ ions

Further Evidence for the Existence of a Dual-Cu⁺ Site in MFI Working as the Efficient Site for C₂H₆ Adsorption at Room Temperature

We have recently clarified the following point: a dual-type site, which is composed of a pair of monovalent copper ions (Cu⁺) formed in a copper-ion-exchanged MFI-type zeolite (CuMFI), functions as the active center for strong ethane (C₂H₆) adsorption even at room temperature rather than a single-type site composed of a Cu⁺ ion. However, the character of the dual-Cu⁺ site in a CuMFI is not yet fully understood. In this study, we have elucidated the nature of the active sites for C₂H₆ based on infrared (IR) and calorimetric data. On the basis of the results obtained, we came to the conclusion that the dual-Cu⁺ site composed of Cu⁺ ions giving the adsorption energy of 100 kJ mol^–1 and the absorption band at 2151 cm^–1 for carbon monoxide (used as a probe molecule) at room temperature functions as an adsorption site for C₂H₆. We also evaluated, for the first time, the interaction between the dual-Cu⁺ site and C₂H₆ energetically, by the direct measurement of heat of adsorption. The value of 67 kJ mol^–1 that we recorded was higher than that for the single-Cu⁺ site in this sample and also for other samples, such as NaMFI and HMFI

Potential for Fixation of N₂ at Room Temperature Utilizing a Copper-Ion-Exchanged MFI-Type Zeolite As an Adsorbent: Evaluation of the Bond Dissociation Energy of Adsorbed NN and the Bond Strength of the Cu⁺−N(N) Species

A peculiar N₂ adsorption was found on a copper-ion-exchanged MFI-type zeolite (CuMFI); the N₂ adsorption was established within 20 s at 300 K. Related to this fact, the bond dissociation energy of NN in a stable Cu⁺−NN species in CuMFI was, for the first time, evaluated to be 9.11 eV from the characteristic bands at 2295, 2654, and 4553 cm⁻¹, which correspond to the fundamental, combination, and overtone vibrations of NN adsorbed on Cu⁺ of CuMFI, respectively. The vibrational frequency of Cu⁺−N in the Cu⁺−NN formed in CuMFI was also determined to be ∼360 cm⁻¹, together with the energy for the formation of a Cu⁺−N bond; the Cu⁺−NN species is stable enough to maintain a N₂ molecule on MFI at 300 K. DFT calculations reasonably explain the experimental data and also the N₂ adsorption model based on the three-coordinate Cu⁺ site in CuMFI