Abstract:Structuring of catalysts and reactors increases the number of degrees of freedom and thus allows tailoring the design for each particular application. Thereby, transport processes can be intensified in order to increase the reactor productivity. This contribution illustrates concepts of structuring on different lengths scales for Fischer‐Tropsch synthesis as example. On this basis the approach of multi‐scale structuring is proposed in order to achieve an improved control of transport processes in chemical reac… Show more
“…This information is crucial for bifunctional core@shell catalysts, as it will influence the surface reactions that take place on the Cu nanoparticles in the core and the heat/mass transport effects which play a role on the µ m scale, i.e. diffusion and reaction in the acidic zeolite (Matera & Reuter, 2012; Grunwaldt et al, 2013; Güttel, 2015). Figure 7 Model of the hierarchically designed core@shell particle showing: ( a ) the shrinkage of the core assuming a simple model consisting of a CuO core and a zeolite shell; ( b ) the observed behavior of the catalyst on the macro-, meso-, and nano-scale.…”
Section: Resultsmentioning
confidence: 99%
“…This information is crucial for bifunctional core@shell catalysts, as it will influence the surface reactions that take place on the Cu nanoparticles in the core and the heat/mass transport effects which play a role on the µm scale, i.e. diffusion and reaction in the acidic zeolite (Matera & Reuter, 2012;Grunwaldt et al, 2013;Güttel, 2015).…”
When using bifunctional core@shell catalysts, the stability of both the shell and core-shell interface is crucial for catalytic applications. In the present study, we elucidate the stability of a CuO/ZnO/Al2O3@ZSM-5 core@shell material, used for one-stage synthesis of dimethyl ether from synthesis gas. The catalyst stability was studied in a hierarchical manner by complementary environmental transmission electron microscopy (ETEM), scanning electron microscopy (SEM) and in situ hard X-ray ptychography with a specially designed in situ cell. Both reductive activation and reoxidation were applied. The core-shell interface was found to be stable during reducing and oxidizing treatment at 250°C as observed by ETEM and in situ X-ray ptychography, although strong changes occurred in the core on a 10 nm scale due to the reduction of copper oxide to metallic copper particles. At 350°C, in situ X-ray ptychography indicated the occurrence of structural changes also on the µm scale, i.e. the core material and parts of the shell undergo restructuring. Nevertheless, the crucial core-shell interface required for full bifunctionality appeared to remain stable. This study demonstrates the potential of these correlative in situ microscopy techniques for hierarchically designed catalysts.
“…This information is crucial for bifunctional core@shell catalysts, as it will influence the surface reactions that take place on the Cu nanoparticles in the core and the heat/mass transport effects which play a role on the µ m scale, i.e. diffusion and reaction in the acidic zeolite (Matera & Reuter, 2012; Grunwaldt et al, 2013; Güttel, 2015). Figure 7 Model of the hierarchically designed core@shell particle showing: ( a ) the shrinkage of the core assuming a simple model consisting of a CuO core and a zeolite shell; ( b ) the observed behavior of the catalyst on the macro-, meso-, and nano-scale.…”
Section: Resultsmentioning
confidence: 99%
“…This information is crucial for bifunctional core@shell catalysts, as it will influence the surface reactions that take place on the Cu nanoparticles in the core and the heat/mass transport effects which play a role on the µm scale, i.e. diffusion and reaction in the acidic zeolite (Matera & Reuter, 2012;Grunwaldt et al, 2013;Güttel, 2015).…”
When using bifunctional core@shell catalysts, the stability of both the shell and core-shell interface is crucial for catalytic applications. In the present study, we elucidate the stability of a CuO/ZnO/Al2O3@ZSM-5 core@shell material, used for one-stage synthesis of dimethyl ether from synthesis gas. The catalyst stability was studied in a hierarchical manner by complementary environmental transmission electron microscopy (ETEM), scanning electron microscopy (SEM) and in situ hard X-ray ptychography with a specially designed in situ cell. Both reductive activation and reoxidation were applied. The core-shell interface was found to be stable during reducing and oxidizing treatment at 250°C as observed by ETEM and in situ X-ray ptychography, although strong changes occurred in the core on a 10 nm scale due to the reduction of copper oxide to metallic copper particles. At 350°C, in situ X-ray ptychography indicated the occurrence of structural changes also on the µm scale, i.e. the core material and parts of the shell undergo restructuring. Nevertheless, the crucial core-shell interface required for full bifunctionality appeared to remain stable. This study demonstrates the potential of these correlative in situ microscopy techniques for hierarchically designed catalysts.
“…Both boarder scenarios and a realistic mixture thereof need flexibility in the involved processes and require unsteady-state or dynamic operation in particular, ensuring stability in all states of the process. The effort to stabilize the dynamic behavior of chemical systems is depending on the tolerance of the system [5] and needs comprehensive understanding of the intrinsic dynamics of all involved sub-processes meaning the processes on different scales [6,7].…”
In this contribution, single pulse reaction experiments are discussed in the context of dynamic reactor operation and used to determine the tolerance of reactors arising from sorption effects at the catalyst surface. A defined amount of CO is dosed together with an internal standard (He) in a constant H2 stream, and the pulse response is observed with reference to the internal standard, which is representing the fluid dynamics of the injected pulse. Different responses are obtained depending on the catalyst mass (Ni/Al2O3) and the operation temperature (170°C-300°C). The tolerance of the reactor can be deduced from the experimental findings. On the one hand, the catalyst adsorption capacity determines the ability to buffer fluctuations at low reaction temperatures (𝑇<220 °𝐶), which are beneficial for full-conversion, overcoming thermodynamic restrictions. On the other hand, temperature determines the transient response of the system and is independent of the catalyst mass. From these findings the study reveals that reactors represent important buffer systems during load changes in dynamic operation modes and provide an intrinsic tolerance originating from sorption processes at the catalyst surface.
“…In structured catalysts, the geometry is fixed by design, in contrast with the random orientation of particles that results from dumping pellets into a column. The geometry can be optimized in several levels and scales because through the structuring, the different phenomena occurring inside the reactor bed (reaction, internal diffusion, heat and mass transfer, pressure drop) are decoupled, introducing new degrees of freedom and, thus, better control. − This decoupling also gives structured catalysts the advantages of ease of scale-up and accurate description of the fluid mechanics …”
Fibrous structures present interesting characteristics as catalyst supports for heat-and mass-transfer-limited reactions. This paper investigates the mass and heat transport behavior of ceramic fiber-based catalysts (catalytic ceramic paper) by applying them to the exothermic reaction of CO 2 methanation. Catalytic experiments were carried out to fit the activity of the catalysts with known kinetics. A fixed-bed reactor model was used to determine the efficiency and efficiency losses caused by different transport phenomena, as well as to perform a sensitivity study focused on heat transfer. The results show that heat transfer limitations are the main cause for losses in reactor efficiency, with steep temperature profiles developing inside the reactor. Poor heat transfer limits the development of highly active catalysts, while pressure drop restricts the flow rate and therefore the productivity. The use of ceramic materials with higher thermal conductivity and increasing the fiber diameter are promising approaches to enhance heat transfer, reduce pressure drop, and improve overall reactor performance.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
