Dokument-ID Dokumenttyp Verfasser/Autoren Herausgeber Haupttitel Abstract Auflage Verlagsort Verlag Erscheinungsjahr Seitenzahl Schriftenreihe Titel Schriftenreihe Bandzahl ISBN Quelle der Hochschulschrift Konferenzname Quelle:Titel Quelle:Jahrgang Quelle:Heftnummer Quelle:Erste Seite Quelle:Letzte Seite URN DOI Abteilungen OPUS4-8104 Dissertation Primus, Philipp-Alexander High resolution spectroscopy as a tool to unravel structure-reactivity relationships in Eu3+ doped ceria/ceria-zirconia based catalyst nanomaterials 2015 89 Institut für Chemie OPUS4-58658 Wissenschaftlicher Artikel Pilar Yeste, Maria; Carlos Hernandez-Garrido, Juan; Kumke, Michael Uwe; Alvarado, Sarah; Cauqui, Miguel Angel; Juan Calvino, Jose; Primus, Philipp-Alexander Low-temperature growth of reactive pyrochlore nanostructures on Zirconia-supported ceria The use of a catalyst support for the design of nanoscale heterogeneous catalysts based on cerium oxide offers vast possibilities for future catalyst development, particularly with regard to an increased focus on the use of renewable biogas and an emerging hydrogen economy. In this study, zirconia-supported ceria catalysts were synthesized, activated by using different thermochemical treatments, and characterized by way of temperature-programmed reduction (TPR), oxygen storage capacity, Xray diffraction, electron microscopy, and luminescence spectroscopy using Eu3+ as a spectroscopic probe. Through reduction-oxidation pretreatment routines, reactive pyrochlore structures were created at temperatures as low as 600 degrees C and identified through TPR and electron microscopy experiments. A structural relationship and alignment of the crystal planes is revealed in high-resolution scanning transmission electron microscopy experiments through the digital diffraction patterns. Low-temperature pretreatment induces the formation of reactive pyrochlore domains under retention of the surface area of the catalyst system, and no further morphological changes are detected. Furthermore, the formation of pyrochlore domains achieved through severe reduction and mild reoxidation (SRMO) treatments is reversible. Over multiple alternating SRMO and severe reduction and severe reoxidation (SRSO) treatments, europium spectroscopy and TPR results indicate that pyrochlore structures are recreated over consecutive treatments, whenever the mild oxidation step at 500 degrees C is the last treatment (SRMO, SRMO-SRSO-SRMO, etc.). Washington American Chemical Society 2022 11 ACS applied nano materials 5 5 6316 6326 10.1021/acsanm.2c00416 Institut für Chemie OPUS4-38926 Wissenschaftlicher Artikel Primus, Philipp-Alexander; Menski, Antonia; Yeste, Maria Pilar; Cauqui, Miguel Angel; Kumke, Michael Uwe Fluorescence Line-Narrowing Spectroscopy as a Tool to Monitor Phase Transitions and Phase Separation in Efficient Nanocrystalline CexZr1-xO2:Eu3+ Catalyst Materials Despite the wide range of industrial applications for ceria-zirconia mixed oxides (CexZr1-xO2), the complex correlation between their atomic structure and catalytic performance is still under debate. Catalytically interesting CexZr1-xO2 nanomaterials can form homogeneous solid solutions and, depending on the composition, show phase separation under the formation of small domains. The characterization of homogeneity and atomic structure of these materials remains a major challenge. High-resolution emission spectroscopy recorded under cryogenic conditions using Eu3+ as a structural probe in doped CeZrO2 nanoparticles offers an effective way to identify the different atomic environments of the Eu3+ dopants and, subsequently, to monitor structural parameters of the ceria-zirconia mixed oxides. It is found that, in stoichiometric CeZrO2:Eu3+, phase separation occurs at elevated temperatures beginning with the gradual formation of (pseudo)cubic crystallites in the amorphous materials at 500 degrees C and a sudden phase separation into tetragonal, zirconia-rich and cubic, ceria-rich domains over 900 degrees C. The presented technique allows us to easily monitor subtle changes even in amorphous, high surface area samples, yielding structural information not accessible by conventional techniques such as X-ray diffraction (XRD) and Raman. Moreover, in reference experiments investigating the reducibility of largely unordered Ce0.2Zr0.8O2:Eu3+, the main reduction peak in temperature-programmed reduction measurements appeared at exceptionally low temperatures below 200 degrees C, thus suggesting the outstanding potential of this oxide to activate catalytic oxidation reactions. This effect was found to be dependent on the amount of Eu3+ dopant introduced into the CeZrO2 matrix as well as to be connected to the atomic structure of the catalyst material. Washington American Chemical Society 2015 11 The journal of physical chemistry : C, Nanomaterials and interfaces 119 19 10682 10692 10.1021/acs.jpcc.5b01271 Institut für Chemie OPUS4-37484 Wissenschaftlicher Artikel Primus, Philipp-Alexander; Ritschel, Thomas; Sigueenza, Pilar Y.; Cauqui, Miguel Angel; Hernandez-Garrido, Juan Carlos; Kumke, Michael Uwe High-resolution spectroscopy of europium-doped ceria as a tool to correlate structure and catalytic activity Site-selective emission spectra of Eu3+-doped CeO2 nanoparticles up to the D-5(0) - F-7(5) transition were recorded under cryogenic conditions to identify the local structure around the Eu3+ dopants in ceria. It is found that pretreatment conditions are crucial for the redistribution of dopants from a broad variety of environments to six well-defined lattice sites. The influence of the dopant and the host structure on the catalytic activity was investigated. A relationship between structure and reactivity is discussed. It is shown that oxygen transport is most efficient in particles with a pronounced amorphous character. Washington American Chemical Society 2014 12 The journal of physical chemistry : C, Nanomaterials and interfaces 118 40 23349 23360 10.1021/jp505467r Institut für Chemie OPUS4-58210 Wissenschaftlicher Artikel Yeste, Maria Pilar; Primus, Philipp-Alexander; Alcantara, Rodrigo; Cauqui, Miguel Angel; Calvino, Juan Jose; Pintado, José María; Blanco, Ginesa Surface characterization of two Ce0.62Zr0.38O2 mixed oxides with different reducibility This paper presents a study of the surface properties of two Ce/Zr mixed oxides with different reducibility, obtained by applying distinct thermal ageing treatments to an oxide with the composition Ce0.62Zr0.38O2. The surface composition was investigated by XPS. Chemical reactivity of the surface was studied by adsorption of the probe molecules CO2, D-2 and methanol. Nanostructural characterization was carried out by XRD, Raman and high-resolution Eu3+ spectroscopy (FLNS). The characterization showed only slight variations in surface composition and bulk Ce-Zr distribution, but hardy differences concerning the type and strength of acidic surface centres, as well as strong differences in the ability to dissociate hydrogen. Structural variations between both samples were identified by comparing the optical spectra of Eu3+ in surface doped samples. Amsterdam Elsevier 2020 9 Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces 503 10.1016/j.apsusc.2019.144255 Institut für Physik und Astronomie OPUS4-7995 misc Mondal, Suvendu Sekhar; Behrens, Karsten; Matthes, Philipp R.; Schönfeld, Fabian; Nitsch, Jörn; Steffen, Andreas; Primus, Philipp-Alexander; Kumke, Michael Uwe; Müller-Buschbaum, Klaus; Holdt, Hans-Jürgen White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+ Co-doping of the MOF 3∞[Zn(2-methylimidazolate-4-amide-5-imidate)] (IFP-1 = Imidazolate Framework Potsdam-1) with luminescent Eu3+ and Tb3+ ions presents an approach to utilize the porosity of the MOF for the intercalation of luminescence centers and for tuning of the chromaticity to the emission of white light of the quality of a three color emitter. Organic based fluorescence processes of the MOF backbone as well as metal based luminescence of the dopants are combined to one homogenous single source emitter while retaining the MOF's porosity. The lanthanide ions Eu3+ and Tb3+ were doped in situ into IFP-1 upon formation of the MOF by intercalation into the micropores of the growing framework without a structure directing effect. Furthermore, the color point is temperature sensitive, so that a cold white light with a higher blue content is observed at 77 K and a warmer white light at room temperature (RT) due to the reduction of the organic emission at higher temperatures. The study further illustrates the dependence of the amount of luminescent ions on porosity and sorption properties of the MOF and proves the intercalation of luminescence centers into the pore system by low-temperature site selective photoluminescence spectroscopy, SEM and EDX. It also covers an investigation of the border of homogenous uptake within the MOF pores and the formation of secondary phases of lanthanide formates on the surface of the MOF. Crossing the border from a homogenous co-doping to a two-phase composite system can be beneficially used to adjust the character and warmth of the white light. This study also describes two-color emitters of the formula Ln@IFP-1a-d (Ln: Eu, Tb) by doping with just one lanthanide Eu3+ or Tb3+. 2014 8 4623 4631 urn:nbn:de:kobv:517-opus4-79953 Institut für Chemie OPUS4-7994 Wissenschaftlicher Artikel Mondal, Suvendu Sekhar; Behrens, Karsten; Matthes, Philipp R.; Schönfeld, Fabian; Nitsch, Jörn; Steffen, Andreas; Primus, Philipp-Alexander; Kumke, Michael Uwe; Müller-Buschbaum, Klaus; Holdt, Hans-Jürgen White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+ Co-doping of the MOF 3∞[Zn(2-methylimidazolate-4-amide-5-imidate)] (IFP-1 = Imidazolate Framework Potsdam-1) with luminescent Eu3+ and Tb3+ ions presents an approach to utilize the porosity of the MOF for the intercalation of luminescence centers and for tuning of the chromaticity to the emission of white light of the quality of a three color emitter. Organic based fluorescence processes of the MOF backbone as well as metal based luminescence of the dopants are combined to one homogenous single source emitter while retaining the MOF's porosity. The lanthanide ions Eu3+ and Tb3+ were doped in situ into IFP-1 upon formation of the MOF by intercalation into the micropores of the growing framework without a structure directing effect. Furthermore, the color point is temperature sensitive, so that a cold white light with a higher blue content is observed at 77 K and a warmer white light at room temperature (RT) due to the reduction of the organic emission at higher temperatures. The study further illustrates the dependence of the amount of luminescent ions on porosity and sorption properties of the MOF and proves the intercalation of luminescence centers into the pore system by low-temperature site selective photoluminescence spectroscopy, SEM and EDX. It also covers an investigation of the border of homogenous uptake within the MOF pores and the formation of secondary phases of lanthanide formates on the surface of the MOF. Crossing the border from a homogenous co-doping to a two-phase composite system can be beneficially used to adjust the character and warmth of the white light. This study also describes two-color emitters of the formula Ln@IFP-1a-d (Ln: Eu, Tb) by doping with just one lanthanide Eu3+ or Tb3+. Cambridge Royal Society of Chemistry 2015 8 Journal of materials chemistry : C, Materials for optical and electronic devices 18 3 4623 4631 10.1039/C4TC02919D Institut für Chemie OPUS4-39355 Wissenschaftlicher Artikel Mondal, Suvendu Sekhar; Behrens, Karsten; Matthes, Philipp R.; Schönfeld, Fabian; Nitsch, Jörn; Steffen, Andreas; Primus, Philipp-Alexander; Kumke, Michael Uwe; Müller-Buschbaum, Klaus; Holdt, Hans-Jürgen White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+ Cambridge Royal Society of Chemistry 2015 9 Journal of materials chemistry : C, Materials for optical and electronic devices 3 18 4623 4631 10.1039/c4tc02919d Institut für Chemie