Almuth Berthold

Contributions of phase composition and defect structure to the long term stability of Li/MgO catalysts

Abstract The phase composition and defect structure of the system Li2O–MgO was investigated in terms of the long term stability of Li/MgO catalysts. The Li content was varied from 0 to 7 mol.%. Pure Li · MgO solid solutions were prepared via a special washing procedure. Li contents below 0.04 wt.% were stabilized within the MgO host lattice, whereas higher Li contents were found to segregate as Li2O and Li2CO3 phases. The catalytic activity in the oxidative coupling of methane was found to decay for all catalysts over a period of 19 h on stream, accompanied by a loss of Li as LiOH. Li in the Li · MgO solid solution was found to be more stable in the lattice than in the surface region of the solid. However, impedance measurements on transition metal stabilized Li/MgO catalysts indicated that even the Li ions within the Li · MgO solid solution are not sufficiently stabilized. Thus, neither the Li compounds nor the dissolved Li ions within the Li/MgO solution seem to be truly stable at 750°C under catalytic conditions.

Li/MgO Catalysts Doped with Alio-valent Ions. Part I: Structure, Composition, and Catalytic Properties

Doping of Li/MgO with additional metal ions is suggested leading to an improved system with respect to the catalytic performance and stability when used for oxidative coupling of methane. We used Gd and Fe as dopants and characterized the resulting materials, showing that Fe seems to be completely and Gd partly incorporated into the MgO lattice. The catalytic performance is improved in most cases, but all materials still suffer from severe deactivation. A loss of Li is observed when being used under reaction conditions, but this Li loss is retarded for Fe‐Li/MgO as compared to undoped Li/MgO.

Flow Through Ceramic Foams – A Future Cell Culture Challenge

Nutrient supply throughout a three-dimensional porous scaffold is a crucial parameter for cell cultivation in perfused bioreactor systems. Cell density and growth patterns strongly depend on (i) the matrix’s flow structures. This is mainly determined by pore openings consolidated during the fabrication process but it can also be imprinted afterwards, e.g. by drilling channels into the matrix. Moreover, cell density and growth depend on (ii) flow velocity through the structure.