Theory of Brønsted Acidity in Zeolites

The nature of the chem. bond of protons in a zeolite is analyzed on the basis of theor. and spectroscopic results. Of interest is the dependence on zeolite structure as well as compn. The zeolitic OH bond is mainly covalent. Proton attachment to the zeolite lattice causes a weakening of neighboring Si-O and Al-O bonds. The effective increase in vol. of the bridging oxygen atom causes a local deformation, that changes the strength of the lattice-chem. bonds over a few bond distances. Proton concn. effects as well as lattice-compn. effects can be understood on the basis of the lattice-relaxation model. The energetics of proton transfer is controlled by the need to stabilize the resulting zwitter-ion. The pos. charge on the cation becomes stabilized by contact with basic lattice-oxygen atom

Application of VAPO-5 in liquid phase oxidation reactions: Indications for the presence of different vanadiumsites

VAPO-5's with different vanadium content (0.18 – 2.0 at%) have been used as catalyst for the liquid phase epoxidation of cinnamylalcohol (3-phenyl-2-propan-1-ol) by t-butylhydroperoxide (TBHP). It has been found that the activity, expressed as turn-over frequency (TOF), increases with increasing vanadium content. Diffuse Reflectance UV VlS (DRUWIS) shows that in samples with a high vanadium content a second type of vanadium species is present that probably is responsible for the observed higher catalytic activity

Entstehung und chemische Natur von Koksablagerungen bei typischen Kohlenwasserstoff-Reaktionen an sauren monofunktionellen Zeolith-Katalysatoren

Copy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Positron emission profiling : a study of hydrocarbon diffusivity in MFI zeolites

Zeolites are of prime importance to the petrochemical industry as catalysts for hydrocarbon conversion. In their molecule-sized micropores, hydrocarbon diffusion plays a pivotal role in the final catalytic performance. Here, we present the results of Positron Emission Profiling experiments with labeled hydrocarbons in zeolites with the MFI morphology. Single-component self-diffusion coefficients of hexanes in silicalite-1 and its acidic counterpart H-ZSM-5 are determined. For the first time, self-diffusion co efficients of n-pentane and n-hexane in mixtures are studied. This shows that Positron Emission Profiling is a powerful technique for in situ investigations of the adsorptive and diffusive properties of hydrocarbons in zeolites. The diffusion of hydrocarbons in medium-pore zeolites is determined by a complex interplay of factors such as the loading, the temperature, the preference for certain pore locations, the interactions with other hydrocarbon molecules of the same type or of other types and the presence of acid protons. In the diffusion of mixtures, pore blockage by one of the components might occur, thus strongly decreasing the diffusivity of the faster diffusing hydrocarbon

Praeparation und Testung von metallbeladenen, durch Ionenaustausch im festen Zustand modifizierten Zeolith-Katalysatoren Schlussbericht

Zeolite catalysts were burdened with metal compounds with the aid of solid state ion exchange, and their activity and selectivity was investigated. Test reactions were hydration and dehydration of model substances. The catalytic efficiency of these zeolite catalysts was found to be equal to that of catalysts produced by conventional means. (EF)Im Rahmen des Forschungsvorhabens wurden Zeolith-Katalysatoren mit Hilfe des Festkoerper-Ionenaustauschs mit Metallverbindungen beladen und ihre Aktivitaet sowie Selektivitaet untersucht. Als Testreaktionen dienten Hydrierung und Dehydrierung von Modellsubstanzen. Es konnte nachgewiesen werden, dass ihr katalytisches Verhalten dem der konventionell hergestellten Katalysatoren ebenbuertig war. (EF)Available from TIB Hannover: F95B33+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

CrAPO-catalyzed oxidations of alkylaromatics and alcohols with TBHP in the liquid phase (redox molecular sieves, part 8)

Chromium-substituted aluminophosphates were synthesized and characterized. Chromium-aluminophosphoates (CrAPO-5 and CrAPO-11) catalyze the oxidn. of ethylbenzene, p-ethyltoluene, n-propylbenzene, n-butylbenzene, diphenylmethane, p-ethylanisole, and primary, secondary benzylic alcs. to the corresponding ketones or acids with TBHP at 80-100 DegC. The main parameters affecting reaction rates are competitive adsorption and diffusion. The activity of used CrAPO-5 is completely recovered by recalcination at 500 DegC. Oxidn. of 4-methoxybenzyl alc. gave 4-methoxybenzoic acid (100% conversion of reactant; 87% selectivity toward product)