Heterogeneous Catalysis: From Fundamentals to Reaction Engineering

The development of new catalytic processes making efficient use of energy and raw materials with minimal impact on the environment is an extremely challenging task. The principal aim of our research is to improve the scientific basis for the advancement of heterogeneous catalytic processes for fine chemical synthesis and the abatement of pollutants that are detrimental to the environment. This aim is pursued with strongly interdisciplinary research embracing fundamental aspects of surface reactions, catalyst design and reaction engineering. Our research strategy and the current projects are briefly discussed

In Situ Monitoring of Heterogeneously Catalyzed Reactions under Supercritical Conditions

A novel high-pressure batch system suitable for in situ monitoring of heterogeneously catalyzed reactions under supercritical conditions is described. The apparatus allows exploration of changes in phase behavior and composition by on-line video imaging as well as on-line sampling and analysis by gas-chromatography using a computer-based approach

Space-Resolved Profiling Relevant in Heterogeneous Catalysis

Knowledge of gradients involved in chemical processes, such as heterogeneously catalyzed reactions, on molecular as well as reactor scale is of paramount importance for understanding and optimizing such processes. This review highlights and discusses recent advances in spatially resolved methods for the detection of chemical (structural) and temperature gradients, with particular focus on in situ method

Advances in Infrared Spectroscopy of Catalytic Solid-Liquid Interfaces: The Case of Selective Alcohol Oxidation

Progress in the use of ATR-IR spectroscopy to improve the understanding of liquid-phase heterogeneous catalytic reactions is illustrated using the example of the oxidation of benzyl alcohol over Pd/Al2O3 and Bi-Pd/Al2O3. The in situ studies performed in both batch and continuous reactor cells provide rich information on the reaction pathway and important facets of the mechanism, such as the nature of active Pd sites and the effect of the Bi-promoter. The combination of CO site blocking prior to reaction and isotopic labeling suggests that alcohol dehydrogenation occurs uniformly over Pd nanoparticles, but only selected sites may allow desorption of the product benzaldehyde thus providing the required selectivity. Promotion of Pd/Al2O3 using bismuth produces infrared spectra free of adsorbed CO. This information demonstrates that Bi is deposited on selected adsorption sites (terraces rather than defects) and simultaneously confirms that open terraces favor product decomposition. Experiments performed in the continuous reactor cell using different catalyst film thickness show that reactions can be studied under kinetic or mass transfer limited conditions depending on catalyst film thickness. This allowed to study the alcohol oxidation under conditions of oxygen diffusion limitation, which are preferably applied in praxis in order to prevent catalyst deactivation by over-oxidatio

Influence of Pt-Ba Proximity on NO x Storage-Reduction Mechanisms: A Space- and Time-Resolved In Situ Infrared Spectroscopic Study

The influence of Pt-Ba proximity on the performance and mechanism of NO x storage-reduction (NSR) was investigated by a comparative study of Pt-Ba/CeO2, Pt/CeO2 and mechanically mixed Pt/CeO2-Ba/CeO2. NO x storage capacity, regeneration activity and selectivity to nitrogen and ammonia during periodic lean (NO+O2)-rich (H2) cycles were evaluated and the chemical gradients along the axial direction of the catalyst beds were monitored by space- and time-resolved in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The presence of Ba and its proximity to Pt greatly influenced the NSR process. In particular, the proximity was crucial to achieve better utilization of bulk Ba components as well as enhancing selectivity to N2. The space-resolved approach is shown to be a powerful tool to understand the impact of the proximity of Pt and Ba constituents on the final NSR performanc

Cobalt‐catalyzed amination of 1,3‐cyclohexanediol and 2,4‐pentanediol in supercritical ammonia

The one‐step procedure of amination of bifunctional secondary alcohols to diamines has been investigated in a continuous fixed‐bed reactor. Application of supercritical NH3 as a solvent and reactant suppressed catalyst deactivation and improved selectivities to amino alcohol intermediates, whereas selectivities to diamines remained poor (8-10%). The main reason for the low diamine selectivity of 1,3‐dihydroxy compounds is water elimination leading to undesired monofunctional products via α,β‐unsaturated alcohol, ketone or amine intermediates. This side reaction does not occur with 1,4‐dihydroxy compounds which afford high aminol and diamine selectivities under similar conditions. Amination of secondary diols with ammonia was found to be faster, but less selective than that of the corresponding primary 1,3‐propanedio

Selective Conversion of Ethane to Ethene via Oxidative Dehydrogenation Over Ca-doped ThO2 Using CO2 as Oxidant

Ca-doped ThO2, synthesized by solution combustion method was tested for dehydrogenation of ethane with CO2. Doping ThO2 with Ca resulted in the creation of oxide ion vacancies and an increased conversion of ethane compared to pure ThO2. On Th0.75Ca0.25O2 selectivity to ethene was 97 at 46% ethane conversion at 725°C. Well-known reference catalysts like 5%Cr/TS-1 or OMS-2 showed significantly lower selectivity, but the former was more active under the same condition

Gold catalysed selective oxidation of alcohols in supercritical carbon dioxide

The oxidation of benzyl alcohol to benzaldehyde over different supported gold catalysts in supercritical carbon dioxide has been investigated in a high-pressure batch reactor. Only molecular oxygen was used as oxidant and no base was needed. Different supports and preparation methods for the catalysts were tested and parameters like reaction temperature, pressure and molar ratios of the components were varied to study the catalytic behaviour. Gold colloids deposited on a titania support (1%Au/TiO2) yielded a conversion of 16.0% after 3h and a high selectivity to benzaldehyde of 99% under single-phase conditions. The reaction rate was significantly higher than in a corresponding "solvent-free” reaction without CO2. Even higher rates were found when a CO2-expanded phase was present. Monitoring of the oxidation in a high-pressure view cell via infrared transmission spectroscopy unravelled a slowdown of the reaction rate above 15% conversion. In addition, 1-octanol and geraniol were oxidised as well under similar conditions, yielding conversions of 4% and 10%, respectively, with selectivities towards octanal and geranial of 90% and 30%. Thus, the combined application of gold-based catalysts and supercritical CO2 offers an interesting alternative to the known methods of alcohol oxidatio

Effect of the Proximity of Pt to Ce or Ba in Pt/Ba/CeO2 Catalysts on NO x Storage-Reduction Performance

The effect of Pt location in Pt/Ba/CeO2 catalysts for NO x storage-reduction (NSR) was analyzed. The Pt location on BaCO3 or CeO2 support was controlled by changing the angle (φ) between the two flame sprays producing these two components. As-prepared flame-made catalysts contain PtO x which must be reduced during the fuel rich phase to become active for NO x storage and reduction of NO x . For Pt on BaCO3 this process was significantly faster than for Pt on CeO2. The increased reduction ability of Pt on Ba is reflected in the light off temperatures: for Pt on CeO2 temperatures around 330°C were needed to combust 20% of C3H6 in air while for Pt on BaCO3 only 250°C were required for the same conversion. The ability to control the location of Pt or other noble metals is, therefore, essential to optimize the catalysts for a given Pt/Ba/CeO2 weight ratio. The best performance was observed when most of the Pt constituent was located near Ba-containing site