The structural properties of finely divided inorganic materials such as metal and metalloid oxides, silicates or carbonates of both synthetic and natural origin are compared by means of electron microscopy and tomography. The structure of the outer surfaces of various compact or compacted agglomerates may suggest some striking similarities between various amorphous silica on the one hand and crystalline titania and alumina on the other however the details of the interior fine structure are completely different. Inside of the crystalline aggregates of, for example, alumina and titania distinct grain boundaries between the inter-grown primary crystallites exist. Also physical boundaries between different solid phases and crystalline/amorphous transitions in core/shell structures can occur. No physical grain or phase boundaries were found inside of synthetic amorphous silica or para-crystalline carbon black thus, the aggregate is the constituent particle. Synthetic amorphous silica from different production technologies (fumed/pyrogenic, precipitated, aerogel, gel) may exhibit different macro-morphology but distinct similarities of the amorphous silica networks. Computational studies on silica and titania underline the stability of constituent particles and aggregates as observed by means of TEM after dispersing the original materials by ultra-sonication.

We conclude that lung surfactant does not promote the disaggregation of TiO2 agglomerates and aggregates.

A simple kinetic model describing the molecular gas phase reactions during the formation of fumed silica (AEROSIL ) was developed. The focus was on the formation of molecular SiO 2 , starting from SiCl 4 , hydrogen and oxygen. Wherever available, kinetic and thermodynamic parameters were taken from the literature. All other parameters are based on quantum chemical calculations. From these data, an adiabatic model for the combustion reaction has been developed. It was found that a significant amount of molecular SiO 2 forms after about 0.1 and 0.6 ms at Die Verbrennung von SiCl 4 in heissen O 2 /H 2-Flammen Inhaltsübersicht. Zur Beschreibung der molekularen Reaktionen in der Gasphase während der Herstellung von pyrogenem Siliciumoxid (AEROSIL ) wird ein einfaches kinetisches Modell entwikkelt. Gegenstand der Arbeiten ist die Bildung von molekularem SiO 2 , ausgehend von SiCl 4. Kinetische und thermodynamische Parameter, die in der Literatur nicht zur Verfügung stehen, werden mit Hilfe von quantenmechanischen Methoden berechnet. Im Rah

Alkane dehydrogenation is of special interest for basic science but also offers interesting opportunities for industry. The existing dehydrogenation methodologies make use of heterogeneous catalysts, which suffer from harsh reaction conditions and a lack of selectivity, whereas homogeneous methodologies rely mostly on unsolicited waste generation from hydrogen acceptors. Conversely, acceptorless photochemical alkane dehydrogenation in the presence of trans-Rh(PMe3 )2 (CO)Cl can be regarded as a more benign and atom efficient alternative. However, this methodology suffers from catalyst deactivation over time. Herein, we provide a detailed investigation of the trans-Rh(PMe3 )2 (CO)Cl-photocatalyzed alkane dehydrogenation using spectroscopic and theoretical investigations. These studies inspired us to utilize CO2 to prevent catalyst deactivation, which leads eventually to improved catalyst turnover numbers in the dehydrogenation of alkanes that include liquid organic hydrogen carriers.

We report the electronic structures and associated optical properties of three inorganic oxides, namely lanthanum oxide, aluminum phosphate, and lanthanum phosphate, calculated by the first principles augmented spherical wave (ASW) and full potential linear muffin tin orbital (FP-LMTO) band structure methods, and the self-consistent field Xα scattered wave (Xα SW) molecular orbital cluster approach. Our calculations indicate negligible effect of the choice of exchange correlation potentials on the position, shape, and relative ordering of the energy bands. The ASW energy gaps in lanthanum phosphate and aluminum phosphate agree satisfactorily with the measured values. A comparison of the electronic density of states for an isolated phosphate group from molecular orbital calculation and that of the valance band from the band structure methods indicates that the nature of bonding within the phosphate groups does not change in aluminum and lanthanum phosphates. The states near the top of the valence band and bottom of the conduction band are mostly due to the phosphate bonding and antibonding orbitals, indicating that optical absorption near the band edge involves excitation of electrons from the bonding levels to antibonding levels associated with phosphate groups. This explains why the optical gaps in many rare earth phosphates are nearly equal.