Norbert Steinfeldt

Tailored Noble Metal Nanoparticles on γ‐Al2O3 for High Temperature CH4 Conversion to Syngas

The simple deposition of tailored Rh or Pt nanoparticles (NP) on γ‐Al2O3 results in active, selective, and stable catalysts for partial oxidation of methane (POM) to syngas. The NP were prepared by the ethylene glycol method in strong alkaline solution. This approach was found to be a promising way of providing active metallic NP for catalyzing the POM reaction. NP sizes determined by small angle X‐ray scattering (SAXS) in solution and by transmission electron microscopy (TEM) on alumina were very close. This result highlights the possibility of easy pre‐characterization of NP by the former method. Supported Rh NP are intrinsically more active in the POM reaction than Pt NP and also showed a superior performance compared with a conventionally prepared Rh catalyst, even if the latter had been pre‐reduced. Mechanistic investigations in the temporal analysis of products (TAP) reactor indicate that the higher selectivity of well‐defined Rh‐NP is determined by their lower activity for consecutive CO transformations.

Boosted Neural Networks in Evolutionary Computation

The paper deals with a neural-network-based version of surrogate modelling, a modern approach to the optimization of empirical objective functions. The approach leads to a substantial decrease of time and costs of evaluation of the objective function, a property that is particularly attractive in evolutionary optimization. In the paper, an extension of surrogate modelling with regression boosting is proposed, which increases the accuracy of surrogate models, thus also the agreement between results obtained with the model and those obtained with the original objective function. The extension is illustrated on a case study in materials science. Presented case study results clearly confirm the usefulness of boosting for neural-network-based surrogate models.

Computing the correlation between catalyst composition and its performance in the catalysed process

Abstract The methodology for computing correlations between continuous descriptors of catalytic materials and their performance in the catalysed process is addressed. Continuous descriptors are typically molar fractions of individual components of the catalyst, whereas the performance is represented most frequently by yield or selectivity of reaction products or conversion of key feed components. Measures of various kinds of correlation are recalled, and their descriptor-wise application to catalytic data for computing correlations between the composition and performance of catalysts is presented. The paper also compares the application of correlation measures to catalytic data on the one hand with the analysis of variance, on the other hand with the application of regression trees. As a case study, the presented approaches are applied to data from high-temperature synthesis of hydrocyanic acid.

Polymer Encapsulated Cobalt-Based Catalysts (Co EnCatTM) for Selective Continuous Hydrogenation of 1-Iodo-4-nitrobenzene

New cobalt catalysts confined in an EnCatTM polyurea matrix by micro‐encapsulation of Al5Co2 or Al5Co2/Al3Ni2 phase containing alloys are disclosed for the reductive hydrogenation of 1‐iodo‐4‐nitrobenzene 1. The product 4‐iodo‐aniline 2 readily undergoes hydro‐desiodination and was used to demonstrate the extraordinary selectivity. Co EnCatTM significantly suppressed this follow‐up reaction under both batch and flow modes. The correlation between performance, elemental composition, and alloy content is presented for these novel catalysts. Among them, the hybrid micro‐encapsulated Co‐Ni catalyst showed higher activity than its Ni‐free analogue. In the flow process, this catalyst gave a high yield of 2 and very low level of 3. Hence, these novel Co EnCatTM catalysts hold promise with respect to the continuous‐flow hydrogenation of challenging halogenated nitroaromatic compounds.

On the selective aerobic oxidation of benzyl alcohol with Pd/Au-nanoparticles in batch and flow

Abstract Nanoparticles (NP) have specific catalytic properties, which are influenced by parameters like their size, shape, or composition. Bimetallic NPs, composed of two metal elements can show an improved catalytic activity compared to the monometallic NPs. We, herein, report on the selective aerobic oxidation of benzyl alcohol catalyzed by unsupported Pd/Au and Pd NPs at atmospheric pressure. NPs of varying compositions were synthesized and characterized by UV/Vis spectroscopy, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). The NPs were tested in the model reaction regarding their catalytic activity, stability, and recyclability in batch and continuous procedure. Additionally, in situ extended X-ray absorption fine structure (EXAFS) measurements were performed in order to get insight in the process during NP catalysis.

Innovative Reactors for Determining Kinetics of Highly Exothermic Heterogeneous Catalytic Reactions

For highly exothermic catalytic reactions particular measures have to be taken for obtaining reliable kinetic and mechanistic information, which has been preferably determined under the prevalence of isothermicity, and which is not disguised by transport processes. If this is true such kinetics can be reliably extrapolated to conditions outside the frame of experimental conditions. To this end various reactor set-ups are presented and their operation is illustrated by some case studies. The temperature-scanning reactor, which is not inherently isothermal, is included since non-isothermicity is not an obstacle to easy kinetic data assessment. Its performance is clarified by estimating kinetic parameters for the ammonia synthesis at elevated pressure using a commercial catalyst. Two types of novel micro-structured reactors are presented which have been applied for two highly exothermic catalytic reactions, i.e., the oxidative dehydrogenation of propane (ODP) and the ammonia oxidation to N2, N2O and NO. These studies served the purpose of getting mechanistic insights into the reaction mechanisms of both reactions, to validate a kinetic scheme for the ODP reaction and to derive the estimates of the respective kinetic parameters. Finally, a reactor for transient experiments in the peak pressure range of 1 to 10 Pa has been used for studying reaction steps related to the catalytic ammonia oxidation under isothermal conditions. Isothermal studies are possible due to the low concentrations of reactants by which any undesired hot spots on the catalyst surface were suppressed. The instrumental arsenal described is an asset for both fundamental as well as applied work in studying exothermic catalytic reactions.

Preparation of tailor-made supported catalysts using asymmetric flow field flow fractionation and their application in hydrogenation

Abstract The optical, chemical, and catalytic properties of metallic nanoparticles (NPs) depend strongly on their particle size and shape. Therefore, the preparation of monodisperse metallic NPs is very important for fundamental studies and practical applications. However, the isolation of the different structures by separation from a polydisperse sample, especially in the size range below 10 nm, is not well applied so far. Here, the asymmetric flow field flow fractionation (AF4) is adapted for the preparative separation of the Pd NPs regarding their size and shape in the sub-10-nm size range. To prove the efficiency of the applied method, small-angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (TEM) were utilized to determine the particle size distribution at different stages of the separation process. A major benefit of this method compared to most of the other separation techniques, the removal of impurities during the separation process, was proven by proton nuclear magnetic resonance (NMR). The obtained results demonstrate that the AF4 is well suited for the rapid preparation of the purified uniform precious metal NPs at the applied size range. Single fractions of the different-sized and -shaped Pd NPs were deposited on titania (TiO2) and tested in the catalytic hydrogenation of 2,5 hydroxymethylfurfural (HMF) in aqueous solution under mild conditions. While the spherical-shaped particles show a high activity, the separated agglomerated particles show a higher selectivity to the desired products.