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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 Article88 28 - 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 Article58 42 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Glycerol hydrogenolysis goes SMART - separating reaction steps as a key for tailoring selectivity and reaction control(American Chemical Society (ACS), 2026-05-27); ; ; ; The next generation of flexible, efficient, and robust chemical processes requires adaptive, resilient, and autonomous process systems that drive the transition from fossil to renewable feedstocks as one of the central challenges in building climate-neutral and sustainable chemical value chains. One central element will be the next generation of reactors that are SMART -Sustainable, Multipurpose, Autonomous, Resilient, and Transferable- merging process engineering with materials science, analytics, electronics, and data science. Herein, the chemical hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO) was used as a case study for tailoring selectivity and reaction control by coupling modeling with experimental approaches for process control, demonstrating adaptive reactor behavior. In detail, the reaction was split into a high-temperature step for the endothermic glycerol dehydration under an inert atmosphere and a consecutive low-temperature step under a hydrogen atmosphere, optimizing the reaction conditions for both reactions and deducing individual kinetic parameters by a graphical analysis of one-factor-at-a-time variations and a global nonlinear regression for the temporal concentration data. The results yield a reaction order of around 0.27 for glycerol with an activation energy of 43 kJ mol−1 for the dehydration step as well as reaction orders of zero for acetol and around 2.15 for hydrogen at an activation energy of 57 kJ mol−1 for the hydrogenation step. The simulated concentration profiles highlight the good agreement between the model and the experimental data. This allows for the implementation of the two-step reaction in a SMART reactor, strengthening the vision of a future generation of autonomous, resilient, and transferable process systems.Publicationtype: Journal Article58 53 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Comparison of acidic and alkaline oxidative catalytic fractionation processes to recover aromatic monomers from native poplar wood and straw digestates: a critical Lab-to-Lab comparisonLignin from native lignocellulose is a potentially attractive raw material for the production of bio-based aromatics due to its high abundance and its aromatic structure rich in ether bonds. Several oxidative catalytic fractionation processes have been presented in literature, through which oxygenated aromatics can be obtained from native lignocellulose-containing biomass in high yields. These processes can be divided into acidic processes using catalysts such as heteropolyacids in alcoholic solvents and alkaline processes using copper catalysts in aqueous NaOH solutions. Some of these processes have been tested only in one laboratory so far and the comparability among each other is very limited. Consequently, it is the aim and main novelty of this study to reproduce these processes with poplar wood and to compare them among each other and with the well-established reductive catalytic fractionation using the same reactor setup and biomass sample. The reaction conditions from selected reference processes were reproduced, with the main deviation that a smaller reactor size was used. Highest monomer yields on lignin basis around 40 wt% were obtained by reductive catalytic fractionation, leading to reduced instead of oxygenated monomers. The tested one-step alkaline oxidative catalytic fractionation process resulted in monomer yields up to around 30 wt%. Lowest yields around 10 wt% were obtained for one-step acidic catalytic processes using a methanol–water mixture as solvent and phosphomolybdic acid as catalyst, for which similar monomer yields could be achieved using sulfuric acid instead of phosphomolybdic acid. An acidic two-step process yielded very low monomer yields around 2 wt% largely deviating from literature values. For all oxidative catalytic processes, lower yields compared to literature values were observed, which is comprehensively discussed. It appears that, compared to the stable monomers obtained by reductive catalytic fractionation, the instability of the oxygenated monomers leads to a higher vulnerability to changes in the reaction process, probably shifting the optimal conditions. Straw digestate was applied as alternative substrate and yielded significantly less monomers than poplar wood.Publicationtype: Journal Article14 8 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Boosting the chemical hydrogenolysis of glycerol to 1,2-propanediol to almost perfect selectivity using a multifunctional Ru–Cu carbon-nanotube-supported catalyst(American Chemical Society (ACS), 2026-04-03); ; ; Chemical hydrogenolysis of glycerol to propanediols is a promising strategy for biomass valorization. However, the demanding reaction conditions and deviating requirements for the individual reaction steps cause significant challenges to date. Herein, a kinetic study for the chemical hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO) as well as an optimized reaction procedure using a multifunctional Ru–Cu/CNT catalyst is presented. In detail, it was shown that the glycerol hydrogenolysis reaction is neither influenced by mass nor heat transfer limitations under the applied reaction conditions. Consequently, the following kinetic parameters could be deduced both by experimental determination as well as kinetic modeling: n (glycerol) = 1.1, n (H2) = 0.12 up to 25 bar (kinetic regime), and an activation energy of 150 kJ mol–1 for the desired 1,2-PDO pathway, as well as n (glycerol) = n (H2) = 0 for the undesired ethylene glycol pathway at an activation energy of around 65 kJ mol–1. Moreover, separating glycerol hydrogenolysis into two steps, initial glycerol dehydration to acetol under a nitrogen atmosphere at a high temperature of 220 °C, followed by acetol hydrogenation to 1,2-PDO under a hydrogen atmosphere at a low temperature of 145 °C using the same Ru–Cu/CNT catalyst, can lead to higher overall yields and almost perfect selectivity for 1,2-PDO. This could be verified in a separate experiment showing acetol selectivity of >99% for the first and 1,2-PDO selectivity of >99% for the second step without observable ethylene glycol production. Compared to the combined reaction under standard hydrogenolysis conditions of 50 bar H2 and 220 °C, almost perfect 1,2-PDO selectivity could be achieved, showing great potential for the separate approach. Moreover, a kinetic model of the glycerol hydrogenolysis based on the experimentally derived reaction rates confirms that the models reliably reproduce the observed reaction behavior with respect to the observed kinetic parameters.Publicationtype: Journal Article96 56 - 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 Article88 81 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Advanced glycerol oxidation to formic acid in a multiphasic jet loop reactor using polyoxometalate catalysts(American Chemical Society (ACS), 2026); ; ; ; Glycerol is a common byproduct of commercial biodiesel production and can be used for the production of green platform chemicals such as biogenic formic acid (FA). Biogenic FA is industrially produced via selective catalytic oxidation in the OxFA process using various biomass in conventional stirred-tank reactors (STR). However, the reaction is limited by the low oxygen solubility in the aqueous reaction media that typically requires high oxygen pressures of 10–30 bar. This study aims to implement the multiphasic selective oxidation of glycerol to FA in a jet loop reactor (JLR), highlighting the economic and mass transfer advantages compared to the conventional used STR. The multiphasic approach was catalyzed by the homogeneous H5PV2Mo10O40 (HPA-2) polyoxometalate catalyst, already established in the commercial OxFA process. The reactor characterization indicates an efficient and high gas–liquid mass transfer, achieving volumetric mass transfer coefficient values (kl · a values) ranging from 51 to 173 h–1. Afterward, the multiphasic glycerol oxidation reaction to FA was implemented and compared in both reactor concepts under identical reaction conditions. The JLR achieved very high FA space-time-yields (STY) of up to 30.0 gFA LR–1 h–1, highlighting its improved mass transfer and favorable economics already at 5 bar oxygen pressure in a simple glass setup. Determination of the kinetic parameters in the JLR resulted in reaction orders of 0.83 for glycerol and 0.54 for oxygen underlining the importance of an efficient gas–liquid mass transfer. Moreover, the activation energy was determined to be 78.3 kJ mol–1, which is well in line with previous studies carried out for the OxFA process in a STR. The calculated Hatta number of 0.014 for the multiphasic glycerol oxidation in the JLR indicates that the reaction is in the kinetic regime already at low oxygen pressures of 5 bar demonstrating the high potential of the reactor concept for future studies.Publicationtype: Journal Article75 67 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , The nature of lignin and implications for its technical use as a source for biogenic aromatics — a review(Multidisciplinary Digital Publishing Institute (MDPI), 2025-10-28); ; The composite material lignocellulose makes up the majority of biomass on earth and is characterized by a high biological and chemical resistance, which is essentially caused by the phenylpropanoid polymer lignin. Thus, the removal and depolymerization of lignin to produce aromatic chemicals can significantly enhance the material usability of all lignocellulose constituents. This review summarizes the current state of knowledge on the nature of lignin, including its biosynthesis, structure, chemistry and biodegradation. Second, it attempts to derive implications regarding the technical valorization of lignin from native biomass through depolymerization. Finally, the consequences of the findings for conventional, recently developed and future processes valorizing lignocellulose are assessed, and the associated technical and economic hurdles are discussed. It becomes clear that lignin depolymerizability is restricted in established pulping processes, primarily due to repolymerization reactions. Strategies avoiding lignin repolymerization involve an increased process complexity and additional economic expenditure but might enable an increased value creation from lignocellulosic biomass.Publicationtype: Review Article32 12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , ProFA - Valorization of macroalgae biomass as source of proteins and formic acid(Royal Society of Chemistry (RSC), 2025-05-26); ; ; ; Macroalgae are promising feedstocks for the sustainable production of bioplastic films from proteins or platform chemicals such as formic acid (FA) as they are valuable sources of proteins and carbohydrates. This study explores the possibility of using macroalgae as biomass for biogenic FA production using the OxFA process in combination with the extraction of proteins from macroalgae with a focus on resource utilisation and innovation. Herein, the extraction of proteins and the utilisation of the other components of macroalgae to produce FA is linked for the first time. The aim was to find out which macroalgae is best suited to produce FA and protein-rich solids. For this purpose, three different algae were tested: The brown alga Fucus vesiculosus, the green alga Ulva fenestrata and the red alga Porphyra dioica. In addition, the most suitable catalyst for this study was selected from the two polyoxometalates H5PV2Mo10O40 (HPA-2) and H8PV5Mo7O40 (HPA-5) known for their suitability in the OxFA process. After Porphyra dioica proved to be a promising substrate, the parameters temperature (80 °C – 120 °C), reaction time (18 h – 30 h) and catalyst/substrate ratio (0.05 to 0.5) were evaluated for their statistical influence using a Box-Behnken design of experiments. The resulting model was then used to optimise the protein content and FA yield. The optimal conditions were determined to 80 °C, 30 hours and a catalystto-substrate ratio of 0.5 resulting in a protein yield of 59.5 % and a formic acid yield of 16.4 %. For protein extraction from the solid residues, three different methods such as alkaline hydrolysis, ultrasound-assisted extraction (UAE) and ionic liquid extraction (ILE) were investigated. All extraction methods resulted in a protein recovery of more than 40 %dw, with UAE yielding the highest protein recovery of 87.2 %dw (at 100 % sonication amplitude) showing 30 % higher protein recovery than alkaline hydrolysis and 40 % higher protein recovery than ILE. It turned out that the OxFA process followed by protein extraction using UAE gave a high protein recovery and a promising yield of formic acid.Publicationtype: Journal Article45 51 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Spatially resolved reaction profiles of CO2 hydrogenation to methanol using in-based catalysts in a compact profile reactor(American Chemical Society (ACS), 2024-06-07); ; ; ; The compact profile reactor (CPR) design allows for the simultaneous acquisition of species, temperature, and spatially resolved reaction profiles during high-pressure CO2 hydrogenation to methanol. Indium-based catalysts for CO2 hydrogenation have attracted significant scientific interest since they are more selective, efficient, and resistant to deactivation compared to the state-of-the-art copper-based catalyst. In this study, the reaction profile of In2O3/ZrO2 catalysts is compared to that of the state-of-the-art Cu/ZnO/Al2O3 (CZA) catalyst in a high-pressure CPR. It is demonstrated that the addition of nickel as a promoter significantly enhanced the catalytic activity of pure In2O3/ZrO2. The characterization by H2 TPR and CO2 TPD revealed an increased capacity for both hydrogen and CO2. A detailed comparison and optimization of reaction conditions using Ni–In2O3/ZrO2 as a catalyst are presented. In an optimized experiment, Ni–In2O3/ZrO2 produces 4.90 gMeOH gIn+Ni–1 h–1 at 275 °C, 50 bar, and 63,000 h–1with a methanol selectivity of 73%. Furthermore, no catalyst deactivation caused by metal leaching or sintering could be observed over 90 h time on stream.Publicationtype: Journal Article216 134