18 research outputs found

    Renewable butene production through dehydration reactions over nano-HZSM-5/γ-Al2O3 hybrid catalysts

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    The development of new, improved zeolitic materials is of prime importance to progress heterogeneous catalysis and adsorption technologies. The zeolite HZSM-5 and metal oxide γ-Al2O3 are key materials for processing bio-alcohols, but both have some limitations, i.e., HZSM-5 has a high activity but low catalytic stability, and vice versa for γ-Al2O3. To combine their advantages and suppress their disadvantages, this study reports the synthesis, characterization, and catalytic results of a hybrid nano-HZSM-5/γ-Al2O3 catalyst for the dehydration of n-butanol to butenes. The hybrid catalyst is prepared by the in-situ hydrothermal synthesis of nano-HZSM-5 onto γ-Al2O3. This catalyst combines mesoporosity, related to the γ-Al2O3 support, and microporosity due to the nano-HZSM-5 crystals dispersed on the γ-Al2O3. HZSM-5 and γ-Al2O3 being in one hybrid catalyst leads to a different acid strength distribution and outperforms both single materials as it shows increased activity (compared to γ-Al2O3) and a high selectivity to olefins, even at low conversion and a higher stability (compared to HZSM-5). The hybrid catalyst also outperforms a physical mixture of nano-HZSM-5 and γ-Al2O3, indicating a truly synergistic effect in the hybrid catalyst

    Microkinetic modeling of the Water-Gas Shift reaction over cobalt catalysts supported on multi-walled carbon nanotubes

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    The development of microkinetic models allows gaining an understanding of fundamental catalyst surface phenomena in terms of elementary reaction steps without a priori defining a rate-determining step, yielding more meaningful and physically reliable reaction rates. This work aimed at developing such a microkinetic model that accurately describes the Water-Gas Shift (WGS) reaction, i.e., one of the major routes for hydrogen production, over cobalt (Co) catalysts supported on multi-walled carbon nanotubes (MWCNTs). Co is known for its sulfur-tolerance and the functionalized MWCNT support has exceptional conductivity properties and defects that facilitate electron transfer on its surface. The model was formulated based on a well-known mechanism for the WGS reaction involving the highly reactive carboxyl (COOH*) intermediate. The kinetic parameters were computed by a combination of calculation via theoretical prediction models (such as the Collision and Transition-State theory) and via regression to the experimental data. The derived system of differential-algebraic equations was solved using the DDAPLUS package available in the Athena VISUAL Studio. The developed model was capable of simulating the experimental data (R² = 0.96), presenting statistically significant kinetic parameters. Furthermore, some of the catalyst descriptors in the model have been related to the catalyst properties as determined by characterization techniques, such as the specific surface area (SP = 22,000 m²/kgcat) and the density of active sites (σ = 0.012 molAct.Surf./kgcat). The modelling and characterization efforts allowed identifying the COOH* formation reaction (CO* + OH* → COOH* + *) as the surface reaction with the highest activation energy. Optimal catalyst performance, resulting in a CO conversion exceeding 85%, was simulated at elevated temperatures (350–450 °C) and space times (70–80 kg·s/mol), in agreement with the experimental observations

    NiCu-based catalyst design for the hydrodeoxygenation of bio-derived model compounds

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    Door de uitputting van fossiele grondstoffen en bijbehorende milieuproblemen is er behoefte aan hernieuwbare alternatieven. Lignocellulose is een ruimschoots beschikbare biomassa die niet concurreert met voedselproductie. Met behulp van verschillende processen die de hydrodeoxygenatiereactie gebruiken (HDO) kan de biomassa omgezet worden in zowel biobrandstoffen als chemicaliën. Echter, huidige HDO-katalysatoren, gebaseerd op de petroleumindustrie, zijn niet optimaal voor biomassa. Deze thesis richt zich op het vervangen van deze katalysatoren door NiCu katalysatoren die specifiek ontworpen worden voor deze hernieuwbare bronnen. NiCu op γ-Al2O3-drager bleek veelbelovend, maar miste stabiliteit. Diverse stoffen, zoals Ca, Mg, Ce en La, zijn getest voor modificatie om de katalysorprestaties te verbeteren. Ca verbeterde de stabiliteit, maar verminderde de selectiviteit voor gedeoxygeneerde producten. Ce en La beïnvloedden de activiteit en selectiviteit, afhankelijk van de impregneervolgorde. Sequentiële impregnering met La voor NiCu verbeterde de stabiliteit aanzienlijk. Ook voor valorisatie van furfural-afgeleide verbindingen toonden (La-)NiCu-katalysatoren potentieel, waarbij de drager een cruciale rol speelde. La toevoegen versterkte de activiteit opmerkelijk. Dit onderzoek levert een belangrijke bijdrage aan het optimaliseren van NiCu-katalysatoren voor HDO, biedt een kosteneffectief alternatief en bevordert duurzame productie van koolstofneutrale brandstoffen en waardevolle producten, bijdragend aan een duurzamere toekomst

    Enhancing stability of γ-Al2O3-supported NiCu catalysts by impregnating basic oxides in the hydrodeoxygenation of anisole

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    Basic oxides such as CaO and MgO were added to a γ-Al2O3 support in NiCu-catalyzed hydrodeoxygenation of anisole. A commercial CaO-MgO-γ-Al2O3 was compared to a benchmark γ-Al2O3 and in-house variants with sequential oxide impregnation prior to NiCu impregnation. CaO did not have a significant impact on activity compared to the benchmark, while MgO improved NiCu dispersion, enhancing activity. Co-impregnation of CaO and MgO resulted in intermediate activity. Despite decreased demethoxylation, likely due to moderated support acidity, both CaO-modified and the commercially supported catalysts showed improved stability over 48 h Time On Stream

    Impact of oxygen vacancies in Ni supported mixed oxide catalysts on anisole hydrodeoxygenation

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    The hydrodeoxygenation (HDO) activity of anisole has been investigated over Ni catalysts on mixed metal oxide supports containing Nb-Zr and Ti-Zr in 1:1 and 1:4 ratios. XRD patterns indicate the incorporation of Ti (or Nb) into the ZrO2 framework. XPS and oxygen pulse chemisorption analyses reveal that Ni/Ti1Zr4 and Ni/Nb1Zr4 possessed more oxygen vacancy sites than Ni/Ti1Zr1 and Ni/Nb1Zr1, respectively. Correspondingly, the HDO activity of Ni/Ti1Zr4 and Ni/Nb1Zr4 was higher with an anisole conversion up to 30.7 and 34.4%, with high selectivity towards benzene (up to 64.7 and 63.3%), compared to corresponding Ni/Ti1Zr1 and Ni/Nb1Zr1 catalysts
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