Study of Au/SnO x –Al2O3 catalysts used in CO oxidation by in situ Mössbauer spectroscopy

The active catalytic components in tin oxide containing alumina-supported gold catalyst were examined by comparing and analysing the in situ Mössbauer spectra of the SnO _x –Al₂O₃ support and the 3 wt.% Au/SnO _x –Al₂O₃ catalyst (1.1 wt.% Sn, Au/Sn = 3:2 atomic ratio). Samples were prepared by using organometallic precursor of ¹¹⁹SnMe₄ (enriched). First tin was grafted to the alumina surface from the organometallic precursor compound. In the next step the grafted complexes were decomposed in flowing oxygen. Gold was deposited onto the SnO _x –Al₂O₃ support in the subsequent step. Analysis of in situ spectra shows that in Au/SnO _x –Al₂O₃ catalyst after activation in hydrogen at 620 K tin may occur in three different oxidation states [Sn (IV), Sn(II) and Sn(0)] simultaneously. The metallic tin is a component of the bimetallic AuSn alloy phase. Data presented provide the first evidence for the formation of alloy-type supported Sn–Au catalyst on alumina. Furthermore, from the spectra recorded at different temperatures, values of the Debye temperatures and recoilless fractions were also determined for the various species. The results show that in catalytic oxidation of carbon monoxide at room temperature the dominant part of Sn(II) and the AuSn alloy is oxidized.     

Focusing,collimation and flux throughput at the IMCA‐CAT bending‐magnet beamline at the Advanced Photon Source

The IMCA‐CAT bending‐magnet beamline was upgraded with a collimating mirror in order to achieve the energy resolution required to conduct high‐quality multi‐ and single‐wavelength anomalous diffraction (MAD/SAD) experiments without sacrificing beamline flux throughput. Following the upgrade, the bending‐magnet beamline achieves a flux of 8 × 10¹¹ photons s^?1 at 1 Å wavelength, at a beamline aperture of 1.5 mrad (horizontal) × 86 µrad (vertical), with energy resolution (limited mostly by the intrinsic resolution of the monochromator optics) δE/E = 1.5 × 10^?4 (at 10 kV). The beamline operates in a dynamic range of 7.5–17.5 keV and delivers to the sample focused beam of size (FWHM) 240 µm (horizontally) × 160 µm (vertically). The performance of the 17‐BM beamline optics and its deviation from ideally shaped optics is evaluated in the context of the requirements imposed by the needs of protein crystallography experiments. An assessment of flux losses is given in relation to the (geometric) properties of major beamline components.     

1H and 13C MAS NMR studies of light alkanes activation over MFI zeolite modified by Zn vapour

The early stages of methane, ethane and propane conversion were studied by in situ ¹H and ¹³C MAS NMR techniques over fully exchanged Zn²⁺/MFI catalyst obtained by the reaction with zinc vapour. The in situ techniques revealed strong interaction of alkanes with Zn²⁺ cations evidenced by significant shift of the corresponding NMR lines. Besides that, the formation of methyl zinc, ethyl zinc and n-propyl zinc species along with bridging and silanol surface OH-groups was detected already at the ambient temperature. These results pointed to dissociative adsorption of alkanes over (ZO)–Zn²⁺–(OZ) and (ZO)–Zn²⁺–(OSi) active sites of the catalyst. The dissociative adsorption was shown to be a dead-end surface reaction in the case of methane starting reactant, while in the case of ethane and propane, it appeared to be responsible for the initiation of the catalytic cycle leading to alkenes and dihydrogen formation and regeneration of zinc containing catalytic sites.     

New tin(IV) complexes with sterically hindered o‐iminobenzoquinone ligand: Synthesis and structure

The reduction of 4,6‐di‐tert‐butyl‐N‐(2, 6‐di‐iso‐propylphenyl)‐o‐iminobenzoquinone (imQ) by tin amalgam in hexane solution leads to new six‐coordinated o‐iminoquinonato tin(IV) complex (iSQ)₂SnAP ( 1 ) (where iSQ and AP are o‐iminosemiquinolate and dianion o‐amidophenolate, respectively). Variable temperature magnetic susceptibility measurements of 1 have shown that this complex possesses a weak ferromagnetic exchange between o‐iminosemiquinonate ligands. The oxidation of 1 with air oxygen produces new o‐iminoquinonolate tin(IV) derivatives [(iSQ)Sn(AP)]₂O ( 2 ) and (iSQ)₂Sn(OH)₂ ( 3 ) containing μ‐oxo‐ and hydroxo‐ligands, respectively. The electronic structure of 1 was examined by DFT analysis. Complexes 1–3 have been investigated using single‐crystal X‐ray diffraction. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:332–340, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20555     

Supercontinua for high-resolution absorption multiplex infrared spectroscopy

Supercontinua generated in highly nonlinear fibers by ultrashort-pulse lasers can be used for high-resolution Fourier transform absorption spectroscopy. The practical advantages of these bright ultrabroadband light sources for spectroscopy in the near-infrared region are reported. A Cr(4+):YAG femtosecond laser broadened by an extruded soft-glass photonic crystal fiber, emitting from 1200 to 2200 nm and from 675 to 950 nm, provides a spectral radiance 1 x 10(5) times higher than that of a 3000 K blackbody and 10(2) times higher than that of synchrotron radiation. The C(2)H(2) and NH(3) overtone spectra are recorded by using this source within a few seconds.     

Crystallization of segmented trans-1,4-polyisoprene/epoxidized trans-1,4-polyisoprene block copolymers from solution

The crystallization of segmented block copolymers of trans-1,4-polyisoprene (TPI)/expoxidized TPI from solution was investigated. One preparation with an average TPI block length of 14.5 and an average epoxidized TPI block length of 10 was crystallized from 2-pentanol at 20°C, 2-octanol at 20°C, and 2-pentanone at 0°C. A second preparation with an average TPI block length of 18 and the same average epoxidized TPI block length was crystallized from 2-octanol at 20°C and 2-pentanone at 0°C. The crystallization products were expoxidized in suspension a second time and then characterized by carbon-13 solution NMR to determine the average noncrystalline traverse length and the average crystalline stem length. The crystallized products were also studied by scanning electron microscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry to determine the morphology, the crystal form and crystallinity, and the melting point, respectively. The average noncrystalline traverse length was found to be highly dependent on the crystallization conditions and the crystalline stem length of the parent TPI lamellas; the composition of these traverses is discussed.     

Mathematical morphology operations with a comparator array processor

We present a demonstrator photonic system for mathematical morphology image processing. Optically interconnected arrays of differential pairs of optoelectronic transceivers realize morphological erosion and dilation in an 8x8 pixel size image.     

Effect of ionization on the temperature- and pressure-induced phase transitions of poly(N-isopropylacrylamide) gels

The ionization effects on the pressure-induced phase transition of weakly charged poly(N-isopropylacrylamide-co-acrylic acid) (PNIPA-AAc) gels have been investigated by small-angle neutron scattering. At low temperature, T, and pressure, P, the structure factor of PNIPA-AAc gels was well represented by a Lorentzian (L) function, which was similar to noncharged PNIPA gels. However, at high Ps, the contribution of inhomogeneities became large and a squared-Lorentzian term had to be added in addition to the L term. At high Ts, on the other hand, a scattering maximum appeared, indicating microphase separation. This scattering maximum was suppressed by increasing P up to P approximately 100 MPa and then reincreased at higher Ps. The following facts were disclosed: (1) The peak position and height were very sensitive to P, which is mainly ascribed to strong pressure dependence of hydrophobic interaction, (2) ionization leads to microphase separation at elevated temperatures, (3) the re-entrant phase behavior is commonly observed in the P-T plane due to the parabolic variation of the polymer-solvent interaction with P, and (4) the pressure and temperature dependence of the structure factor was reproduced with the Rabin-Panyukov theory and was interpreted with a convexity of hydrophobic interaction with respect to pressure.