Arbejdsprøve med Kunstgødningsspredere paa Dalum Landbrugsskole i Efteraaret 1908.

Arbejdsprøve med Kunstgødningsspredere paa Dalum Landbrugsskole i Efteraaret 1908

Selective Catalytic Reduction of NOx by CO over Cu(Fe)/SBA-15 Catalysts: Effects of the Metal Loading on the Catalytic Activity

Mesoporous Cu(Fe)/SBA-15 catalysts were prepared with distinct metal loadings of ca. 2–10 wt.%. A detailed set of characterizations using X-ray diffraction (XRD), electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), scanning electron microscopy coupled to energy dispersive spectroscopy (SEM-EDS), Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy was performed to correlate the relationship among structure, electronic properties and catalytic performances. All solids were evaluated in the selective catalytic reduction of NOx in the presence of CO (CO-SCR). The influence of the metal loadings on the overall activity indicated that introducing high amounts of Fe or Cu on the catalysts was beneficial to form either CuO or α-Fe2O3 clusters. Cux/SBA-15 series exhibited more efficient activity and poison-tolerant ability during CO-SCR reaction, in contrast to Fex/SBA-15. In spite of the Fe species introduced on SBA-15 having structural features similar to those of Cu ones, low interactions among Fe nanoparticles, silica and clusters impeded the high performances of Fe10/SBA-15. XPS revealed the Fe species in a more oxidized state, indicating the stability of the solid after the catalytic tests, in agreement with EPR and Raman spectroscopy. Cu8/SBA-15 worked better, being recyclable due to the interaction of the Cu2+ ions with SBA-15, avoiding the deactivation of the catalyst.The authors acknowledge the financial support by the Funcap (Grant PS1-0186-00346.01.00/21). A.C.O. and ERC thank to Ministerio de Ciencia e Innovación (Spain) projects PID2021-126235OB-C32 and TED2021-130756B-C31, and FEDER funds. Partial funding for open access charge: Universidad de Málag

Anmeldelser, bekendtgjorte i Statstidende i december måned.

Anmeldelser, bekendtgjorte i Statstidende i december måned

Anmeldelser, bekendtgjorte i statstidende i juli måned.

Anmeldelser, bekendtgjorte i statstidende i juli måned

Katalytische NOx-Entfernung aus mobilen Abgasen an kleinporigen Zeolithen

Zur Entfernung von Stickoxiden aus mobilen Abgasen werden Katalysatoren eingesetzt. In dieser Arbeit wurden kleinporige Zeolithe für diese Anwendung optimiert und verschiedene Charakterisierungsmethoden verwendet, um ein besseres mechanistisches Verständnis zu erlangen. Durch Untersuchungen unter erhöhtem Druck wurde das Potential einer Anwendung vor dem Turbolader betrachtet

Anmeldelser, bekendtgjorte i statstidende i december måned.

Anmeldelser, bekendtgjorte i statstidende i december måned

Anmeldelser, bekendtgjorte i statstidende i september måned.

Anmeldelser, bekendtgjorte i statstidende i september måned

Anmeldelser, bekendtgjorte i statstidende i september måned.

Anmeldelser, bekendtgjorte i statstidende i september måned

A critical analysis of research done to identify conceptual difficulties in acid-base chemistry.

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.The literature review shows that student alternative conceptions or misconceptions are important for teaching and learning. Causes of such student difficulties may include the counter-intuitive nature of some chemistry concepts or to instruction itself. However, over 30 years research into student conceptual difficulties has had little impact on teaching and learning chemistry. In this study, a critical analysis and synthesis of published research into student conceptions in acid-base chemistry was carried out in the naturalist nomothetic paradigm using a constructivist framework. Historical models which were included were an operational macroscopic model and the theoretical Arrhenius and Brønsted models. Firstly, a comprehensive search strategy with defined inclusion/exclusion criteria identified 42 suitable reports which were mostly peer-reviewed. The identified research was not limited to Anglophone countries although Africa and South America were underrepresented and research among secondary students predominated. Then a critique of the research showed it was of variable quality and often poorly reported. An outcome was a set of guidelines for research into student conceptions. The variable quality and reporting of research then also necessitated a four-level framework to reflect the stability of descriptions of student difficulties. A new method for synthesis of descriptions of student conceptual difficulties was developed which entailed mapping qualitative data on the difficulties, which had been extracted from research publications, to propositional knowledge statements derived in this study. This was an iterative process which simultaneously honed descriptions of difficulties and illuminated propositional knowledge implicated in them. The second major outcome was synthesized descriptions of 10 student difficulties with acid-base species, 26 difficulties with acid-base properties and 17 difficulties concerning terminology and symbolism particular to acid-base chemistry. Some conceptions were also found to have been mis-reported as ‘misconceptions’. The difficulties could be broadly due to student conceptions concerning acid-base models, or students not relating empirical observations to theoretical models or their poor understanding of underlying chemical principles. Some difficulties were found to have been over-researched, while further work was needed to clarify the nature some difficulties with conceptions of bases, acid-base reactions, and symbolism used in acid-base chemistry. The third major outcome from the synthesis was 218 propositional knowledge statements which were shown to be suitable for teaching high-school students, avoided hybrid historical models and were acceptable to expert chemists. These propositional statements were integrated as a set of 11 concept maps. The maps showed the hierarchy and interconnectedness of concepts as well as the propositional links which had been implicated in the difficulties. Furthermore the concept maps indicated critical concepts where teaching in each topic should focus as well as cross-linked concepts that can be used to integrate different aspects of the topic. Accordingly they contribute to PCK in the acidbase topic as they represent the fine-grained yet well integrated conceptual knowledge characteristic of a teacher with highly developed PCK