DECHEMA

About: DECHEMA is a nonprofit organization based out in Frankfurt am Main, Germany. It is known for research contribution in the topics: Corrosion & Oxide. The organization has 756 authors who have published 1307 publications receiving 25693 citations.

The nature of the acid sites in mesoporous MCM-41 molecular sieves

Abstract: The objective of this presentation is to give a characterization of aluminosilicate MCM-41, in particular with respect to acidity and the nature of the acid sites 29 Si MAS NMR spectra of MCM-41 closely resemble those of amorphous silica, suggesting that the pore walls are amorphous This fact could also imply that the types of acid sites in these materials are different from those generally found in zeolitic materials The obtained results from 1 H MAS NMR and combined FTIR and temperature-programmed ammonia desorption (TPAD) investigations indicate that the washed, template-free MCM-41 and its protonic form behave as a solid-state acid with a broad acid strength distribution With regard to the presence of bridging hydroxyl groups in the investigated MCM-41 materials, the findings of these two methods are not consistent Therefore, it is assumed that the broad absorption between 3650–3400 cm −1 in the FTIR spectra is connected with hydrogen-bonded vicinal silanol pairs The results of the catalytic testing suggest that the weak Bronsted acid sites interact with neighbouring coordinatively unsaturated aluminium species and that synergistically stronger acid sites are formed

Raman Scattering: Fast Axial Rotation of Methylhalides and Acetonitrile in the Liquid State

Abstract: The temperature dependence of the degenerate methyl stretching Raman profiles of CH3CN, CH3I, CD3I, CH3Cl, and CH3F and, further, for CH3CN the pressure dependence are investigated. The Raman bands are analysed in terms of the small angle diffusion and the J-diffusion model both with and without Coriolis interaction. The comparison with the small angle diffusion model is carried out in the frequency domain. For the analysis in terms of the J-diffusion model, first experimental orientational correlation functions are calculated. Then, by following theoretical arguments, the overall correlation function is decomposed into two partial correlation functions g(2)1(t) and g(2)2(t). There is limited agreement with previous magnetic relaxation studies on the fast axial spinning motion. In particular, it is found that the partial correlation function g(2)2(t) shows little temperature and pressure dependence, which cannot satisfactorily be accounted for by the existing models.

Die thermische polymerisation deuterierter styrole

Abstract: Polymerisationsgeschwindigkeit und STAUDINGERindex verschiedener deuterierter Styrole werden mit und ohne Zusatz von Azoisobuttersauredinitril bestimmt und mit den entsprechenden Werten der nicht markierten Verbindung verglichen. Die Ergebnisse weisen darauf hin, das die Wasserstoffatome in ortho-Stellung zur Vinylgruppe am Startschritt der thermischen Polymerisation des Styrols beteiligt sind. Rate of polymerization and STAUDINGERindex are determined for different deuterium containing styrenes with and without addition of azo-bis-isobutyronitrile. The results were compared with the corresponding values of normal styrene. The results indicate that the hydrogene atoms in ortho-position to the vinyl group participate in the thermal initiation of styrene.