Nanostructured Rhenium Dioxide: Synthesis and Characterization

Abstract

from the present FAU-on-EMT overgrowth material by selectively dissolving the siliceous EMT core, which occurs when the crystallization time is prolonged.Experimental EMT (SiO 2 ) crystals (obtained from Ludox HS-40 (Du Pont)), Gibbsite (Al 2 O 3 , Fluka), NaOH pellets (Merck), 1,4,7,10,13, Acros), and distilled water were mixed according to the following molar ratios [18]: 10 : 1 : 4.8 : 0.97 : 135 respectively. The resulting gel was aged for 3 days at room temperature before crystallization was conducted in a PTFE-lined stainless steel autoclave. After 11 days at 373 K, a wet cake of EMT crystals was recovered by vacuum filtration. 6.0 g of this cake was mixed with 29.1 g of a second gel, prepared in the same way but with a molar NaOH proportion of 7.5. The sample in Figure 3, however, was obtained by adding 13.3 g of the wet EMT cake to 22.4 g of the gel. Crystallization was performed at 373 K without aging. After 3 days, the solid product was recovered by vacuum filtration, washed with deionized water, dried at 333 K, and finally calcined at 823 K in a muffle furnace. The remaining part of the EMT cake was washed with deionized water until the pH of the water was below 10, and then dried at 333 K. Calcination was done in a muffle furnace at 823 K for 20 h.XRD patterns were collected on an automated Siemens D-5000matic diffractometer using Cu Ka radiation. The XRD profiles were recorded in the range of 2y values between 4 and 55 with steps of 0.02 and counting times of 1.2 s. SEM pictures were taken on a Jeol superprobe 733 and on a Philips XL30 FEG apparatus. A gold film was sputtered onto the samples supported on alumina disks prior to observation.HREM investigations were carried out with a 200 kV Philips CM200 Ultra Twin apparatus with a point-to-point resolution of 0.19 nm. The zeolite powder was deposited onto a holey carbon film; the zeolite crystals remained stable under the electron beam irradiation for at least several minutes. By choosing intermediate magnifications, the beam damage could also be minimized.Nitrogen adsorption isotherms at 77 K were recorded using an Omnisorp-100 analyzer from Coulter, operating in the continuous flow mode. Calcined samples were outgassed at 673 K under high vacuum (10 ±6 kPa) for at least 12 h. Micropore volumes were derived from the adsorption isotherm using the t-plot method of Lippens and de Boer. [19] 29 Si MASNMR measurements were performed on a Bruker 400 MSL spectrometer with a magnetic field of 9.4 T. The experiments were run at 79.5 MHz, with a pulse length of 4 ms, a pulse interval of 5 s, a spinning rate of 4 kHz, for 11 000 scans.The use of self-assembled molecular arrays of surfactant molecules as supramolecular templates allows the generation of nanostructured materials. These compounds, exemplified by the Mobil Corporations M41S silica-based phases, [1] tend to show periodicity on the 2±10 nm scale. The formation of this kind of material represents an important step in the quest to control structural order on length scales between atomic and macrosc...

Synthesis and Characterization of Methyltrioxorhenium(VII) Immobilized in Bipyridyl-Functionalized Mesoporous Silica

“…MTO, for example, exhibits an intense sharp pre-edge peak. [24] Any distortion of the regular tetrahedral symmetry leads to a decrease in Figure 6. Re L I -edge XANES spectra of (a) (4,4Ј-dimethyl-2,2Ј-bipyridine)(methyl)trioxorhenium (2), and (b) MCM-41-bpy/MTO the peak intensity.…”

“…In fact, the spectrum of MCM-41-bpy/MTO comes close to that reported for bulk MTO. [24] Figure 7. Re L III -edge XAFS and Fourier transforms for (a) (4,4Ј-dimethyl-2,2Ј-bipyridine)(methyl)trioxorhenium (2), and (b) MCM-41-bpy/MTO; the solid line represents the experimental data and the dashed line shows the best fit using parameters given in Table 2 Table 2.…”

“Hard” vs. “Soft” Templating Synthesis of Mesoporous Nb2O5 Catalysts for Oxidation Reactions

“…Typically, ''hard'' (exo) templates include channel-like alumina membranes [6], track-etched polycarbonates [7], zeolites [8], pristine [9,10] or microwave-digested mesoporous silicas [11], carbon nanotubes [12,13] or spheres [14] and surface-structured solid substrates [15]. Over the past decade various surfactants have been employed as ''soft'' templates for the synthesis of mesoporous molecular sieves, including nanostructured oxides such as rhenium dioxide [16], nickel oxide [17], divanadium pentoxide [18], tin oxide [19,20], MO 2 , where M = Ti, Zr, Ce [21], iron-titanium oxide [22], titanium oxide [23]. This softtemplating synthesis has been commonly used to obtain ordered mesoporous silicas, which in turn were shown to be very promising as ''hard'' templates for the preparation of other inorganic oxides of different structures depending on the architecture of the silica host.…”

Ceramic methyltrioxorhenium

“…6), as revealed by comparable diffraction angles of the hk0 Bragg peaks. Previous X-ray studies 7c of 2 led to a structural model displaying double layers of corner-sharing [CH 3 ReO 5 ] ∞ octahedra interconnected by intercalated water molecules. However, no such 3D ordering can be expected for ceramic MTO since only the hk0 reflection series are evident in the diffraction pattern (Fig.…”