Stability of Cobalt Particles In and Outside HZSM‐5 under CO Hydrogenation Conditions Studied by ex situ and in situ Electron Microscopy

In Situ Transmission Electron Microscopy to Study the Location and Distribution Effect of Pt on the Reduction of Co3 O4 -SiO2

The addition of Pt generally promotes the reduction of Co3 O4 in supported catalysts, which further improves their activity and selectivity. However, due to the limited spatial resolution, how Pt and its location and distribution affect the reduction of Co3 O4 remains unclear. Using ex situ and in situ ambient pressure scanning transmission electron microscopy, combined with temperature-programmed reduction, the reduction of silica-supported Co3 O4 without Pt and with different location and distribution of Pt is studied. Shrinkage of Co3 O4 nanoparticles is directly observed during their reduction, and Pt greatly lowers the reduction temperature. For the first time, the initial reduction of Co3 O4 with and without Pt is studied at the nanoscale. The initial reduction of Co3 O4 changes from surface to interface between Co3 O4 and SiO2 . Small Pt nanoparticles located at the interface between Co3 O4 and SiO2 promote the reduction of Co3 O4 by the detachment of Co3 O4 /CoO from SiO2 . After reduction, the Pt and part of the Co form an alloy with Pt well dispersed. This study for the first time unravels the effects of Pt location and distribution on the reduction of Co3 O4 nanoparticles, and helps to design cobalt-based catalysts with efficient use of Pt as a reduction promoter.

Transient Behavior of CO and CO2 Hydrogenation on Fe@SiO2 Core–Shell Model Catalysts—A Stoichiometric Analysis of Experimental Data

The hydrogenation of CO and CO2 from industrial exhaust gases into CH4 represents a promising method for sustainable chemical energy storage. While iron-based catalysts are in principle suitable for that purpose, the active metal Fe undergoes a complex transformation during the chemical reaction process. However, only little is known about the change in catalytically active species under reaction conditions, primarily caused by structural changes in the catalyst material, so far. By using core–shell model materials, factors that alter the catalyst structure can be excluded, making it possible to observe the direct influence of the reactants on the activity in the present work. Furthermore, stoichiometric analysis was used as a key tool for the evaluation of individual key reactions in the complex reaction network purely from experimental data, thus making it possible to draw conclusions about the catalyst state. In the case of CO hydrogenation, the presumed Boudouard reaction and the associated carburization of the catalyst can be quantified and the main reaction (CO methanation) can be determined. The results of the CO2 hydrogenation showed that the reverse water–gas shift reaction mainly took place, but under an ongoing change in the catalytic active iron phase. Due to the systematic exchange between CO and CO2 in the reactant gas stream, a mutual influence could also be observed. The results from the stoichiometric analysis provide the basis for the development of kinetic models for the key reactions in future work.

Iron Based Core-Shell Structures as Versatile Materials: Magnetic Support and Solid Catalyst

Core-shell materials are promising functional materials for fundamental research and industrial application, as their properties can be adapted for specific applications. In particular, particles featuring iron or iron oxide as core material are relevant since they combine magnetic and catalytic properties. The addition of an SiO2 shell around the core particles introduces additional design aspects, such as a pore structure and surface functionalization. Herein, we describe the synthesis and application of iron-based core-shell nanoparticles for two different fields of research that is heterogeneous catalysis and water purification. The iron-based core shell materials were characterized by transmission electron microscopy, as well as N2-physisorption, X-ray diffraction, and vibrating-sample magnetometer measurements in order to correlate their properties with the performance in the target applications. Investigations of these materials in CO2 hydrogenation and water purification show their versatility and applicability in different fields of research and application, after suitable individual functionalization of the core-shell precursor. For design and application of magnetically separable particles, the SiO2 shell is surface-functionalized with an ionic liquid in order to bind water pollutants selectively. The core requires no functionalization, as it provides suitable magnetic properties in the as-made state. For catalytic application in synthesis gas reactions, the SiO2-stabilized core nanoparticles are reductively functionalized to provide the catalytically active metallic iron sites. Therefore, Fe@SiO2 core-shell nanostructures are shown to provide platform materials for various fields of application, after a specific functionalization.