Gerhard Emig

Large area photochemical dry etching of polyimide with excimer UV lamps

Abstract Large area dry etching and surface modification of polyimide (PI) films was achieved with an incoherent excimer UV source. The transmittance change of thin PI films on fused quartz substrates was determined with an UV spectrophotometer after different exposure times at three different wavelengths: λ=172 (Xe∗2), 222 (KrCl∗) and 308 nm (XeCl∗), respectively. Etch rates of PI were measured at the different wavelengths as a function of UV intensity, exposure time and background pressure in the exposure reactor. The morphology of the exposed areas of the PI films was investigated with SEM. The results are compared with data obtained with mercury UV lamps and excimer laser experiments published by several groups.

Diffusion in Zeolites — a random-walk approach

Abstract In this paper a simple two-dimensional random-walk model for the diffusion of a binary mixture in zeolites is presented. The effects of the ratio of the two molecular diffusion coefficients as well as the maximum loading of a single cage on the concentration dependence of the effective and the corrected diffusion coefficients are investigated.

The Influence Of Water On The Oxydehydrogenation Of Isobutyric Acid Over Heteropolyacid Catalysts

Abstract It has been demonstrated, that for the oxydehydrogenation of isobutyric acid (IBA) over heteropolyacid catalysts water has different effects on the catalyst activity. It hinders the adsorption of the reactant IBA but, on the other hand, accelerates the desorption of the carboxylic acids out of the oxygen vacancies (the reduced sites). A kinetic model taking into account the redox process, the inhibiting effect of water and the rate limiting adsorption of the carboxylic acids has been developed. Based on this model, the kinetically optimal ratio of H 2 O/IBA has been calculated.

A Monte-Carlo simulation of diffusion and reaction in zeolites

Abstract Investigations of two-dimensional models to simulate diffusion and reaction in zeolites with a Monte-Carlo method are presented herein. New results of the simulation of single component diffusion and binary diffusion and a possible method to rescale the obtained diffusion coefficients in real units is presented. The estimation of an accurate activation energy was found to be the most important factor, the other parameters were estimated by simple assumptions. Complex reactions such as a consecutive reaction and xylene isomerisation were simulated with a new model. With this model the selective behaviour of the two reactions was investigated. A Type-III selectivity according to Wheeler was found for the consecutive reaction. For xylene isomerisation, reaction paths were simulated and compared with experimental reaction paths. The composition of the thermodynamic equilibrium was obtained for high transition probabilities and the relative rate constants from the literature could be confirmed. According to the results of the simulations one can conclude that a ratio of the diffusion coefficients of o-, m-, and p-xylene=1:1:1000 is too large to explain the experimentally observed distribution of the xylene isomers and a difference of only one order of magnitude was found.

Novel type of catalyst for the pure dehydrogenation of methanol to formaldehyde

We report here on the first results of investigations on the pure dehydrogenation of methanol on a new type of catalyst which was developed taking into account the geometrical relations between catalyst surface structure and molecular dimensions. The catalyst prepared in this way gives results in conversion and selectivity not reached so far by any other known catalytic system. The catalyst obtained can be described as Na x Li 1−x AlO 2 (0≤x≤1)

Transport Phenomena and Reactions in 13X Type Zeolites

Summary Information about mass transfer processes during heterogeneous catalytic reactions on microporous solids has become of special importance. To investigate both sorption and kinetics of transport and reaction of educts and products, especially of the disproportionation of ethylbenzene on 13X zeolites, a high pressure apparatus with a Berty recycle reactor is described. Diffusion coefficients of aromatic hydrocarbons in 13X type zeolites are measured as dependences on temperature and concentration in the non-reaction sorption region by means of both the high-pressure chromatographic technique and the piezometric method. In particular, a comparative study of the transport parameters for the p-diethylbenzene/13X zeolite system is carried out. The data obtained are in good agreement, especially in the high temperature region. They complement each other with respect to temperature and concentration.

Deactivation of Heteropolyacid Catalysts

Summary For the oxydehydrogenation of isobutyric acid to methacrylic acid on heteropolyacid catalysts in the absence of water in the gas phase an initial, exponential decrease in the product formation due to the adsorption of organic components was found. This short term deactivation can simply be avoided by adding water into the gas phase. The linear, long term deactivation is due to the formation of volatile Mo-species. In the presence of water the Mo loss proceeds much slower but cannot be avoided totally. When the gas phase is saturated with this volatile Mo-species, the Mo content of the catalyst remains constant and the heteropolyacid is stabilized.

Prediction of Zeolites Diffusivities

Abstract In this paper a possible method to predict diffusion coefficients in zeolites is presented. This method consists mainly in a random-walk part and a part of reseating the arbitrary units of the random-walk experiment into real units. The so obtained diffusion coefficients can be compared directly with experimental values. The only necessary input into the procedure is the knowledge of the activation energy for the diffusion process, which has to be obtained by experiments or other types of simulations.