Rainer A. Rakoczy

Impact of Organic Interlayer Anions in Hydrotalcite Precursor on the Catalytic Activity of Hydrotalcite-Derived Mixed Oxides

A series of hydrotalcite‐derived mixed oxides containing different organic interlayer anions in the hydrotalcite precursors have been synthesized and studied as catalysts in the transesterification of glycerol trioctanoate with methanol. There are significant differences in the catalytic activity of these mixed oxides, indicating a great impact of interlayer anions in hydrotalcite precursors. Generally, anions with high charge density and, therefore, high content within the interlayer of the hydrotalcites lead to higher catalytic activity in the derived mixed oxides in contrast to anions with low charge density. An influence of interlayer anions on the structural properties of the hydrotalcites, such as interlayer distance, which is determined by X‐ray diffraction analysis, and on the surface area and pore volume of the corresponding mixed oxides, which are determined by nitrogen adsorption, is obtained. Furthermore, interlayer anions had a significant effect on the thermal stability of the hydrotalcite structure as well as on the pore size distribution of derived mixed oxides.

Hydroconversion of methylcyclohexane on TEOS-modified H-ZSM-5 zeolite catalysts: Production of a high-quality synthetic steamcracker feedstock

Abstract With the advent of the European Auto Oil Programme and comparable legislation in other parts of the world, the aromatics content of gasoline has to be reduced considerably. Therefore, new outlets for surplus aromatics have to be found. Mixed n -alkanes with two and more carbon atoms (C 2+ - n -alkanes) represent a high-quality synthetic feedstock for steamcrackers. Thus, the hydrogenation of aromatics to cycloalkanes followed by their hydroconversion into C 2+ - n -alkanes (predominantly ethane, propane and n -butane) could become a useful process option for converting surplus aromatics into a synthetic steamcracker feed. During hydroconversion of methylcyclohexane to C 2+ - n -alkanes, the catalytic properties of acidic zeolite H-ZSM-5 can be remarkably improved by chemical liquid deposition of tetraethoxysilane. Thereby, the yield of the desired C 2+ - n -alkanes at, e.g., 400 °C can be enhanced from around 77% to nearly 82%. Simultaneously, a drastic diminution of the concentration of external Bronsted acid sites and a significant decrease of the total concentration of Bronsted acid sites were observed by adsorption of, respectively, collidine and pyridine monitored by FTIR spectroscopy. Nitrogen adsorption experiments revealed a slight decrease of the micropore volume. These data are consistent with an extensive deactivation of the active sites on the external surface and in close proximity to the pore openings, the latter leading to pore mouth narrowing or, more likely, to partial pore mouth plugging.

19-O-04-Interference microscopy as a tool of choice for investigating the role of crystal morphology in diffusion studies

Publisher Summary This chapter discusses interference microscopy as a tool of choice for exploring the role of crystal morphology in diffusion studies. Interference microscopy is applied to carry out investigations of the influence of the regular intergrowth effects commonly observed in large silicalite crystals on adsorption or desorption of adsorbate molecules. The intracrystaline concentration profiles measured by the interference microscopy during the adsorption of isobutane are compared with those simulated using the Monte Carlo method. The comparison of the simulated and the measured profiles helps to rule out the uptake of isobutane from gas phase into silicalite crystals directly through the internal interfaces separating the intergrowth sections of the crystals.

Percolation diffusion of guest molecules in NaCaA zeolites: field gradient NMR studies and Monte Carlo simulations

Percolation diffusion of guest molecules in NaCaA zeolite is simulated by the Monte Carlo method and monitored by the pulsed field gradient (PFG) nuclear magnetic resonance (NMR) technique. The simulations are performed to evaluate possible manifestations of anomalous percolation diffusion in NaCaA zeolite observable by PFG NMR. The observation of normal diffusion of ethane in NaCaA by PFG NMR was found to be in agreement with the results of Monte Carlo simulations. The conditions of the observation of anomalous percolation diffusion by PFG NMR are discussed.

Reactions of methylcyclohexane on bifunctional zeolite catalysts

The reactions of methylcyclohexane were studied over bifunctional zeolite catalysts with systematically varied pore width and geometry. The isomerization to other C7-cycloalkanes and the disproportionation to C6- plus C8-, C5- plus C9-, and C4- plus C10-cycloalkanes show distinct shape selectivity effects which are discussed in detail.