| 1. |
- Verziu, Marian, et al.
(författare)
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Hydrogenolysis of lignin over Ru-based catalysts : the role of the ruthenium in a lignin fragmentation process
- 2018
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Ingår i: Molecular Catalysis. - : Elsevier. - 2468-8231. ; 450, s. 65-76
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic performances of two different classes of catalysts containing nickel or/and ruthenium as the active sites were studied in the depolymerisation of lignin isolated from Miscanthus × giganteus. The catalysts were prepared either by coprecipitation (ie, (RuNiMgAlO)x, (RuNiAlO)x, (NiAlO)x, (NiMgAlO)x) or by wet impregnation (ie, Ru/Al2O3) and characterized by nitrogen physisorption (BET), XRD, XPS, NH3-TPD, Raman and H2-TPR techniques. The experimental results indicate that the presence of ruthenium led to dimers as dominant products.
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| 2. |
- Svensson, Fredric G., et al.
(författare)
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Rare-Earth-Modified Titania Nanoparticles : Molecular Insight into Synthesis and Photochemical Properties
- 2021
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:19, s. 14820-14830
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Tidskriftsartikel (refereegranskat)abstract
- A molecular precursor approach to titania (anatase) nanopowders modified with different amounts of rare-earth elements (REEs: Eu, Sm, and Y) was developed using the interaction of REE nitrates with titanium alkoxides by a two-step solvothermal-combustion method. The nature of an emerging intermetallic intermediate was revealed unexpectedly for the applied conditions via a single-crystal study of the isolated bimetallic isopropoxide nitrate complex [Ti2Y((PrO)-Pr-i)(9)(NO3)(2)], a nonoxo-substituted compound. Powders of the final reaction products were characterized by powder X-ray diffraction, scanning electron microscopy-energy-dispersive spectroscopy, Fourier transform infrared, X- ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence (PL). The addition of REEs stabilized the anatase phase up to ca. 700 degrees C before phase transformation into rutile became evident. The photocatalytic activity of titania modified with Eu3+ and Sm3+ was compared with that of Degussa P25 titania as the control. PL studies indicated the incorporation of Eu and Sm cations into titania (anatase) at lower annealing temperatures (500 degrees C), but an exclusion to the surface occurred when the annealing temperature was increased to 700 degrees C. The efficiency of the modified titania was inferior to the control titania while illuminated within narrow wavelength intervals (445-465 and 510-530 nm), but when subjected to a wide range of visible radiation, the Eu3+- and Sm3+-modified titania outperformed the control, which was attributed both to doping of the band structure of TiO2 with additional energy levels and to the surface chemistry of the REE-modified titania.
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| 3. |
- Tiseanu, Carmen, et al.
(författare)
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Local structure and nanoscale homogeneity of CeO2-ZrO2 : differences and similarities to parent oxides revealed by luminescence with temporal and spectral resolution
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:2, s. 703-710
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Tidskriftsartikel (refereegranskat)abstract
- Although homogeneity at the atomic level of CeO2-ZrO2 with a Ce/Zr atomic ratio close to unity is considered to be one of the main causes for the increased total oxygen storage capacity (OSC), the characterization approaches of homogeneity remain a major challenge. We propose a simple, yet effective method, to assess both structural and compositional homogeneity of CeO2-ZrO2 by using Eu3+ luminescence measured with time and dual spectral resolution (emission and excitation). For Eu3+-CeO2-ZrO2 calcined at 750 degrees C, the X-ray diffraction, Raman and High-Resolution Transmission Electron Microscopy data converge to a single pseudo-cubic phase. However, the evolution of Eu3+-delayed luminescence from cubic ceria-like to tetragonal zirconia-like emission reveals the formation of CeO2- and ZrO2-rich nanodomains and provides evidence for early phase separation. For Eu3+-CeO2-ZrO2 calcined at 1000 degrees C, the emission of Eu3+ reveals both structural and compositional inhomogeneity. Our study identifies the differences between the local structure properties of CeO2 and ZrO2 parent oxides and CeO2-ZrO2 mixed oxide, also confirming the special chemical environment of the oxygen atoms in the mixed oxide as reported earlier by Extended X-ray Absorption Fine Structure investigations.
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| 4. |
- Tiseanu, Carmen, et al.
(författare)
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Surface versus volume effects in luminescent ceria nanocrystals synthesized by an oil-in-water microemulsion method
- 2011
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 13:38, s. 17135-17145
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Tidskriftsartikel (refereegranskat)abstract
- Pure and europium (Eu(3+)) doped cerium dioxide (CeO(2)) nanocrystals have been synthesized by a novel oil-in-water microemulsion reaction method under soft conditions. In-situ X-ray diffraction and RAMAN spectroscopy, high-resolution transmission electron microscopy, UV/Vis diffuse-reflectance and Fourier transform infrared spectroscopy as well as time-resolved photoluminescence spectroscopy were used to characterize the nanaocrystals. The as-synthesized powders are nanocrystalline and have a narrow size distribution centered on 3 nm and high surface area of similar to 250 m(2) g(-1). Only a small fraction of the europium ions substitutes for the bulk, cubic Ce(4+) sites in the europium-doped ceria nanocrystals. Upon calcination up to 1000 degrees C, a remarkable high surface area of similar to 120 m(2) g (-1) is preserved whereas an enrichment of the surface Ce(4+) relative to Ce(3+) ions and relative strong europium emission with a lifetime of similar to 1.8 ms and FWHM as narrow as 10 cm(-1) are measured. Under excitation into the UV and visible spectral range, the europium doped ceria nanocrystals display a variable emission spanning the orange-red wavelengths. The tunable emission is explained by the heterogeneous distribution of the europium dopants within the ceria nanocrystals coupled with the progressive diffusion of the europium ions from the surface to the inner ceria sites and the selective participation of the ceria host to the emission sensitization. Effects of the bulk-doping and impregnation with europium on the ceria host structure and optical properties are also discussed.
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