Horn, Raimund

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Valorization of different types of biomass via polyoxometalates to formic acid derivatives and desired solid products
(2026-03-30)
Wesinger, Stefanie
;
Horn, Raimund
This dissertation deals with the utilization of various biomass using polyoxometalate (POM) catalysts. Formic acid as well as its derivatives and solid valuable products like proteins from the ProFA process and cellulose from the POM-ionosolv process were produced. The solid value products depended on the starting biomass used. A cellulose-rich solid was produced from lignocellulosic biomass and a protein-rich solid from algae-based biomass. The first part of the dissertation deals with the production of cellulose-rich solids and formic acid or its derivatives. For this purpose, the lignocellulosic biomass was first fractionated using different methods (organosolv and ionosolv) which were subsequently compared with regard to further oxidation using POM catalysts. The ionosolv method proved to be a promising method as more formic acid could be produced. Using a tributylmethylphosphonium methylsulfate ionic liquid (IL) and methanol as co-solvent, a white, cellulose-rich solid with over 90 % glucan was successfully produced. Furthermore, the production of formic acid/formic acid derivatives using POM catalysts in different solvents was investigated. In particular, the solvent-catalyst interaction of the solvent best suited for the production of cellulose-rich solids was investigated using various analytical techniques. It was found that a POM-IL salt forms in the IL/methanol solvent in-situ, which has different selectivities to methyl formate as a formic acid derivative depending on the IL. In the second part of the dissertation, the production of protein-rich solids from macroalgae was investigated using the OxFA (Oxidation of lignocellulosic biomass to formic acid) process. Different types of macroalgae (red algae (Porphyra dioica), brown algae (Fucus vesiculosus) and green algae (Ulva fenestrata)) as well as two different POM catalysts (H5PV2Mo10O40 and H8PV5Mo7O40) were screened. Applying the most promising combination, Porphyra dioica and H5PV2Mo10O40, an optimization study was performed using a Box-Behnken Design of Experiments. This allowed the formic acid yield to be increased from 8.6 % to 16.4 % in combination enabling a protein recovery of 59.5 %. In order to further increase the protein recovery, three promising extraction methods (alkali hydrolysis, ultrasound-assisted extraction and IL extraction) were tested and optimized. Ultrasoundassisted extraction was identified as the best method enabling a protein recovery of 87.2 %. The findings of this dissertation have helped to evaluate the possibilities of POM catalysts in biorefinery-like concepts and to further develop these concepts.
Publicationtype: Doctoral Thesis
48 59
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Measuring adsorbate proﬁles in heterogeneous catalytic reactors by iso-potential operando DRIFTS applied to CO2 methanation on Ni
(2026)
Sichert, Sebastian
;
Horn, Raimund
This work introduces the novel methodology of Iso-Potential Operando Spectroscopy (IPOS) using DRIFTS to simultaneously measure surface adsorbate profiles and concentration and temperature gradients in catalytic reactors under operando reaction conditions. To demonstrate this concept, CO2 methanation on Ni/γ-Al2O3 catalysts is used as a test system. During measurements, formate surface-adsorbed species are indicated as reaction intermediates following the associative reaction pathway.
Publicationtype: Doctoral Thesis
43 25
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Selective oxidation of ethylene to ethylene oxide on silver catalysts at industrial conditions: reactor profiles, kinetics and chlorine inhibition
(2025)
Berg, Viktor
;
Horn, Raimund
In this work, the direct epoxidation reaction of ethylene to ethylene oxide and the influence of cofeeding halogenated hydrocarbons was investigated. Kinetic investigations were conducted to determine intrinsic parameters using a newly designed and constructed isotherm fixed-bed reactor and a compact profile reactor (CPR), which was used to fit the kinetic parameters from measured concentration and temperature profiles at industrial reaction conditions. Also, the CPR was used to study the mechanism of chlorine moderation of the supported silver catalyst, revealing the competitive adsorption behavior of chlorine and oxygen on the same active sites. A pilot-scale reactor was designed and built to validate the kinetic parameters by a 2D pseudohomogeneous profile simulation.
Publicationtype: Doctoral Thesis
68 132
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Operando structure-activity profiling in fixed-bed reactors using synchrotron-based X-Ray techniques
(2023)
Wollak, Birte
;
Horn, Raimund
In this work a method was developed allowing for the simultaneous measurement of species concentration-, temperature-, and X-ray absorption or X-ray diffraction profiles through a fixed-bed reactor using synchrotron radiation. The method provides a comprehensive insight into catalytic reactors under operation, promoting an efficient and sustainable optimization of catalytic processes in the future. The strengths of the method were demonstrated by studying the oxidative dehydrogenation of ethane over supported molybdenum oxide catalysts, revealing the interplay between local reaction conditions and catalyst structure.
Publicationtype: Doctoral Thesis
158 76
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Liquid phase profile reactors for the epoxidation of propylene to propylene oxide on titanium silicalite-1 catalyst: spatially resolved measurements and numerical simulations
(2023)
Aquino, Andres
;
Horn, Raimund
This work constitutes the first application of the spatial sampling technique to study a liquid phase reactions. The reaction under study is the (HP-PO) process. A compact profile reactor was used to study the reaction under industrial conditions. Two models from the scientific literature and a new model proposed within this work were used to simulate the experimental data. A pilot scale reactor with a internal diameter comparable to those in technical scale (HP-PO) reactors was implemented to compare the performance of a bed packed with catalyst extrudates against a bed constituted by additively manufactured open cell structures.
Publicationtype: Doctoral Thesis
104 82
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Resolving gradients in an ammonia oxidation reactor under industrial conditions
(2022)
Pottbacker, Jan
;
Horn, Raimund
In this work a new bench scale setup is presented that enables studies of the underlying processes of ammonia oxidation under industrial, mass transfer controlled conditions by spatially resolved profile measure ments. Measurements in the developed profile reactor are compared with computational fluid dynamics simulations of ammonia oxidation to explain the measured phenomena and to validate the surface kinetic model used in the simulations. All in all, the develo ped approach presented in this work allows to spatially resolve the processes in ammonia oxidation under industrial conditions providing a wealth of data for future process optimization.
Publicationtype: Doctoral Thesis
322 302
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Development and characterization of polymetric gas separation membrandes for catalytic reactions
(2021)
Weigelt, Fynn
;
Horn, Raimund
Publicationtype: Doctoral Thesis
64
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Spatially resolved probing of diffusion and reaction in porous catalyst pellets
(2020)
Sosna, Bahne
;
Horn, Raimund
In the (petro)chemical industry, catalytic fixed-bed reactors packed with porous catalyst pellets are amongst the most widely employed types of reactors. The performance of these reactors in terms of product yield at the reactor outlet is determined by the interplay between diffusion and reaction inside each individual catalyst pellet. For decades, researchers in industry and academia alike have strived to optimize - through analytical and numerical simulation results and integral measurements - pellet size, shape, pore network, and orientation to the flow; and spatial distribution of the active component. To this date, operando measurements of concentration profiles inside porous catalyst pellets were not available. Industrial catalyst pellets are generally non-transparent and thus inaccessible by optical methods; gas spin densities are too low for magnetic resonance imaging, and traditional sampling methods are inadequate when considering the minute diffusional fluxes. In this work, a method was developed to directly measure spatially resolved concentration profiles inside a single catalyst pellet under reaction conditions, by employing a capillary sampling method. CO oxidation on a platinum-coated, porous alumina cylinder was chosen as a test reaction system. CFD simulations were conducted to ascertain the invasiveness of the proposed method; it was hence deemed acceptable for practical applications. Spatially resolved mole fraction profiles of products and educts, inside and in the boundary layer of the particle, are presented for different reaction conditions. Furthermore, phenomena that result from the interplay between diffusion and reaction such as boundary layers, bifurcation, multiple steady states, and kinetic oscillations are shown. Additionally, the possibility of coupling this method with Raman microscopy to gain spatial concentration and temperature profiles from the gas phase was explored. Overall, the developed method could allow the knowledge-based optimization of many industrial fixed-bed processes, without requiring major changes to the process layout.
Publicationtype: Doctoral Thesis
674 690
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Modeling chemistry and flow in catalytic fixed-bed reactors with detailed geometry
(2018)
Dong, Ying
;
Horn, Raimund
In this work, three-dimensional CFD models were developed and applied to simulate catalytic fixed bed reactors with different types of packing configuration and reactions. A spatially resolved profile measurement technique was applied in this work to critically validate the simulation results, and to calibrate parameters required in the model. This work demonstrates that detailed reactor modeling and profile measurements are useful tools for achieving an in-depth understanding of the interactions between flow, heat and mass transfer and catalytic reactions in fixed bed reactors. Furthermore, with the comprehensive knowledge gained from both methods, a knowledge-based reactor optimization approach can be put forward.
Publicationtype: Doctoral Thesis
610 4453

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