The growing production of biodiesel as a renewable source-based fuel leads to an increased amount of glycerol. Thus, it is a favorable starting material to obtain highly functionalized products. From a variety of catalytic reactions three examples, namely glycerol oxidation, glycerol hydrogenolysis and aqueous-phase reforming, were chosen for detailed studies in our group. The experimental focus for the oxidation of glycerol was set on preparation and detailed examination of supported Pt-Bi catalysts in batch reactions as well as in continuous experiments using a trickle bed reactor. For aqueous-phase reforming of glycerol to hydrogen the addition of tin to supported platinum catalysts was investigated. Ruthenium and copper based catalysts could be successfully applied in the hydrogenolysis of glycerol to 1,2-propanediol.

The selective oxidation of glycerol to dihydroxyacetone is still a challenging task for heterogeneous catalysis and important to the chemical industry. Especially bimetallic Pt-Bi catalysts show a high initial selectivity to dihydroxyacetone in acidic media but exhibit a strong deactivation during reaction as well. This deactivation decreases activity as well as selectivity to dihydroxyacetone. Thus, only moderate yields may be achieved. In this work, product adsorption was identified as a major cause. In particular, glyceric acid, an oxidation product of the primary hydroxyl group, selectively blocks those kinds of active sites that are predominantly responsible for dihydroxyacetone formation. This could be confirmed by means of kinetic modeling. It has been proven that all catalytic experiments taken into account for the parameter estimation are free from external and internal transport limitations. A mechanism characterized by two different active sites has been derived. Glyceric acid selectively inhibits one of them, causing the observed decrease in dihydroxyacetone selectivity and catalyst activity.

It is investigated whether the catalyst system Ag-In/SiO 2 can be applied in the selective hydrogenation of citral, with the aim of synthesizing the acyclic, allylic terpene alcohols geraniol/nerol with high selectivity and space-time yield. In addition, as liquid-phase hydrogenations are often also influenced by the choice of solvent, it is of interest to know how the solvent, in particular in terms of its polarity and hydrogen solubility, affects the activity and the selectivity of catalysts during hydrogenation of the a,b-unsaturated aldehyde citral. ProblemTerpenes are a low-cost class of compounds for the production of fragrances, flavors and pharmaceuticals, with terpenoid hydrocarbons (e.g., myrcene) being used less than terpene alcohols (e.g., geraniol, nerol, citronellol) and aldehydes (e.g., citral, citronellal). The compounds are often extracted from essential oils (e.g., lemon grass oil, citrus oil) by fractional distillation. Geraniol is the most frequently used terpenoid fragrance compound and, like its isomer nerol, applied in perfumes of roses and in citrus fragrances [1,2]. As an a,b-unsaturated aldehyde citral itself is an important educt for the synthesis of terpene alcohols and aldehydes because of its three functionalities (carbonyl group, conjugated C=C bond, isolated C=C bond) and thus, with the right choice of catalyst and reaction conditions, enables the synthesis of geraniol/ nerol, citronellal and/or citronellol by selective hydrogenation. Fig. 1 shows the reaction network of citral hydrogenation up to the completely hydrogenated reaction product 3,7-dimethyloctan-1-ol.In academia, citral hydrogenation is often used as a model reaction to study the influence of metal specificities, support materials and solvents on the intramolecular selectivitiy and product yield [3][4][5][6]. From a vulcano plot of the specific activity (turnover frequency) vs. the %-d character [7] of the metal used at 300 K and 0.1 MPa hydrogen pressure it follows, as expected, that Pd is the most active metal, whereas Ni, Co and Rh catalysts exhibit an activity which is about one to two orders of magnitude lower [6] (1) = 3,7-dimethyl-2-octenal, (2) = dihydrocitronellal, (3) = 3,7-dimethyl-2-octenol, (4) = 3,7-dimethyloctan-1-ol.

The synthesis of ceria‐based mixed oxides via an oxalate‐gel method and the testing of their catalytic activity in the carboxylation of methanol with CO2 are described. The evaluation of their activity is performed in liquid phase. With ceria, the influence of pressure, reaction temperature, and composition of the reactants in the gas and liquid phase are investigated. Moreover, the thermodynamics of the reaction and the structural properties of the catalysts, characterized by X‐ray diffraction, FTIR‐ and UV/VIS spectroscopy, and physisorption, are discussed.

SummaryPolymethylmethacrylate (PMMA)/ceria composite fibres were synthesized by using a sequential combination of polymer electrospinning, spray-coating with a sol, and a final calcination step to yield microstructured ceria tubes, which are composed of nanocrystalline ceria particles. The PMMA template is removed from the organic/inorganic hybrid material by radio frequency (rf) plasma etching followed by calcination of the ceramic green-body fibres. Microsized ceria (CeO2) tubes, with a diameter of ca. 0.75 µm, composed of nanocrystalline agglomerated ceria particles were thus obtained. The 1-D ceramic ceria material was characterized by X-ray diffraction, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), UV–vis and photoluminescence spectroscopy (PL), as well as thermogravimetric analysis (TGA). Its catalytic performance was studied in the direct carboxylation of methanol with carbon dioxide leading to dimethyl carbonate [(CH3O)2CO, DMC], which is widely employed as a phosgene and dimethyl sulfate substitute, and as well as a fuel additive.