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Item type:Publication, Access status: with files , Lagrangian μ-particle tracking velocimetry analysis of microscale flow over structured surfaces(American Chemical Society (ACS), 2026-10-08); ; ; ; This work aims to provide an experimental basis for the improvement of (bio)reactors by studying flow over micro- and nanostructured surfaces, with a focus on microscale mass transport toward and away from the surface. μ-Particle tracking velocimetry is employed in a microreactor to experimentally obtain Lagrangian trajectories of flow-following tracer particles. The method also resolves three-dimensional, time-dependent velocity fields. The derived mean velocity profiles agree well with the theory of flow over porous walls. Beyond averaged Eulerian velocities, the Lagrangian framework captures near-surface interactions. The Lagrangian analysis of different surfaces indicates that rectangular structured microgrooves increase the wall contact of the tracer particles, especially when the flow is oriented perpendicular to the microgrooves. Particularly, this approach enables resolution of trapping phenomena and localized recirculation dynamics. Nanostructuring by growing a carbon nanotube forest increases surface area and modifies local fluid dynamics, thereby enhancing contact with (bio)catalysts that are potentially functionalized on the nanotubes in future applications.Publicationtype: Journal Article40 13 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Impact of permeability of triply periodic minimal surface-based substrates on multiwalled carbon nanotube growth(American Chemical Society (ACS), 2026-08-05); ; ; ; Lumpp, DominiqueDue to their excellent thermal and electrical properties combined with pronounced porosity, carbon nanotube forests are promising as catalyst support materials for smart reactors. To maximize catalytic turnover, it is essential to increase the available surface while maintaining precise control over reactant flow and heat distribution. In this work, multiwalled carbon nanotubes are grown on three-dimensional substrates based on triply periodic minimal surfaces, which offer superior mechanical properties alongside controlled flow dynamics and enhanced heat transfer rates. The substrates are fabricated via laser powder bed fusion and subsequently coated using injection chemical vapor deposition. To evaluate the design limitations of the three-dimensional substrates for CNT growth, the impact of a decreasing permeability on the coating’s morphology is investigated. As the permeability decreases with the unit cell size of the triply periodic minimal surfaces and the introduction of an external wall, the characteristic CNT forest structure gradually transforms. Provided that permeability and precursor accessibility to the internal surfaces remain sufficiently high, the morphology and composition of CNT forests closely resemble those grown on flat substrates. Introducing the wall leads to a transition from vertically aligned CNT forests to horizontally oriented CNT networks due to enhanced laminar-like flow characteristics. While less dense, it offers an increased CNT quality. Below a critical minimal permeability, carbon nanostructures with numerous defects form. The successful coating and control of its morphology enable the utilization of the CNT for further smart tailoring of the reactor.Publicationtype: Journal Article87 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Investigations on the role of support and synthesis procedure for the Rux–Cuy/CNT‐catalysed hydrogenolysis of glycerol to 1,2‐propanediol(Wiley, 2026-07-14); ; ; Tailoring support effects plays an important role for controlling activity and selectivity in heterogeneously catalyzed gas–liquid reactions. Sophisticated carbon supports like single‐ and multiwall carbon nanotubes (CNTs) as well as in house produced Globugraphite were used for the synthesis of bimetallic Ru–Cu catalysts, which were tested in a multibatch reactor setup for the chemical hydrogenolysis of glycerol to 1,2‐propanediol (1,2‐PDO) in aqueous solution. In‐depth characterization using multiple tools like inductively coupled plasma optical emission spectrometry, CHNS‐O analysis, N₂‐physisorption, scanning electron microscopy, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, powder X‐ray diffraction, H₂‐temperature programmed reduction, laser diffraction, and point of zero charge measurements revealed the dominating effects that the various carbon supports exert on the catalytic performance. The best‐performing catalyst synthesized by wetness impregnation consisted of Ru–Cu₃ nanoparticles (NPs) from mixed RuCl₃ and Cu(NO₃)₂ precursors dispersed on multiwall CNT Baytubes with a productivity of p = 12.74 g₁,₂‐PDO gactive metal ⁻¹ h⁻¹ . Its superior activity combined with high 1,2‐PDO selectivity (S= 75%) can be explained both by the nature of the highly dispersed Ru and Cu NPs showing the lowest reduction peak temperature on entangled tubes of CNT agglomerates demonstrating a high mesopore volume for optimal reactant accessibility and the highest specific surface area of all investigated materials. This lays the foundation for implementing this highly active and selective catalyst in a future SMART reactor for glycerol valorisation.Publicationtype: Journal Article57 40 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Multifunctional carbon‐nanotube supported catalyst for efficient glycerol hydrogenolysis to 1,2‐propanediol(Wiley, 2026-03); ; Multiwall carbon nanotube (NC7000) supported mono-, bi-, and trimetallic catalysts were synthesized and tested in a multi- batch reactor setup supported by data-driven modeling for the chemical hydrogenolysis of glycerol to 1,2-Propanediol (1,2-PDO) at 220◦C under 30 bar hydrogen pressure in aqueous solution. ICP-OES, N2 -physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDX), powder x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) were used to investigate the physico-chemical properties of the synthesized catalysts. Interesting structure-activity-selectivity correlations could be deduced from the different metal ratios and combinations. While Ru was by far the most active monometallic species ( X = 100%), followed by Pt ( X = 80%) and Ir ( X = 65%), it suffered from a very low 1,2-PDO selectivity ( S < 10%). Combining Ru with the more selective transition-metals RuX2 ( X = Fe, Co, or Ni) maintained the high activity ( X > 95%) but only moderately increased 1,2-PDO selectivity ( S = 20%–30%). Interestingly, combining Ru with Cu in a bimetallic RuCu2 catalyst slightly decreased activity ( X = 81%) but drastically improved 1,2-PDO selectivity ( S = 58%). Moreover, a trimetallic combination of RuMCu2 (M = Pt, Pd, Ir) did not further increase activity ( X = 50%–70%) but could push 1,2-PDO selectivity up to 79% for the trimetallic RuIrCu2 catalyst. Most prominently, a final metal ratio variation for the RuCux catalyst was derived with the help of the data-driven models producing the most promising RuCu3 /NC7000) catalyst combining both high activity ( X = 78%) with a very high 1,2-PDO selectivity ( S = 79%) resulting in the highest 1,2-PDO yield of 58% in a nearly closed carbon balance ( C > 95%). This lays the foundation for implementing this highly active and selective catalyst in a future SMART reactor for glycerol valorization.Publicationtype: Journal Article86 77