Titanium dioxide is one of the most intensely studied oxides due to its interesting electrochemical and photocatalytic properties and it is widely applied, for example in photocatalysis, electrochemical energy storage, in white pigments, as support in catalysis, etc. Common synthesis methods of titanium dioxide typically require a high temperature step to crystallize the amorphous material into one of the polymorphs of titania, e.g. anatase, brookite and rutile, thus resulting in larger particles and mostly non-porous materials. Only recently, low temperature solution-based protocols gave access to crystalline titania with higher degree of control over the formed polymorph and its intra- or interparticle porosity. The present work critically reviews the formation of crystalline nanoscale titania particles via solution-based approaches without thermal treatment, with special focus on the resulting polymorphs, crystal morphology, surface area, and particle dimensions. Special emphasis is given to sol-gel processes via glycolated precursor molecules as well as the miniemulsion technique. The functional properties of these materials and the differences to chemically identical, non-porous materials are illustrated using heterogeneous catalysis and electrochemical energy storage (battery materials) as example.

No abstract

No abstract

Operando XAS measurements in the near (XANES) and the extended (EXAFS) Au L III edge as well as in situ diffuse reflectance FTIR (DRIFTS) spectroscopy were employed in combination with kinetic measurements in a further attempt to identify the nature of the active Au species responsible for the high activity of Au/CeO 2 catalyst in the lowtemperature water gas shift (LT-WGS) reaction. The changes in the reaction behavior during the LT-WGS were followed at 180 °C for different initial states of the catalyst, prepared by either reducing or oxidizing pretreatments at different temperatures. Findings from kinetic and deactivation measurements were correlated with experimental data on the Au particle size, the Au oxidation state, and the CO-Au adsorption properties directly after different pretreatments and during the subsequent LT-WGS reaction obtained by operando/in situ spectroscopy measurements. The combined experimental results show that the use of different pretreatments can significantly influence the electronic state of the Au species (Au δ-, Au 0 , Au δ+ ). Exposure to the reaction atmosphere under the present reaction conditions, however, results in the rapid formation of extremely small, (sub)nanometer-sized Au 0 nanoparticles, which are the dominant Au species and responsible for the high WGS activity. Small amounts of oxidic gold species (Au 3+ ) persisting during reaction after the strongly oxidative O400 pretreatment, in the few percent range, are too little to be responsible for the catalytic activity of that catalyst and changes therein with time on stream.

Abstract. Changes of the geometric and electronic structure of gold on Au/CeO 2 catalysts induced by different pre-treatments (oxidative and reductive) and by the CO oxidation reaction at 80°C were followed by operando XANES / EXAFS measurements. The results showed that i) oxidative pre-treatment (O 2 ) leads to larger Au nanoparticles than reductive pre-treatment (CO), that ii) Au is predominantly metallic during CO oxidation, irrespective of the preceding pre-treatment, and that iii) there is a reaction induced Au particle growth. Correlations with the activity of the respective catalysts and its temporal evolution give insights into the origin of deactivation of these catalysts under reaction conditions, in particular on reaction induced changes in the Au particle size.