FG Technische Chemie
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- CO2 methanation (2)
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Institute
Among challenges implicit in the transition to the post–fossil fuel energetic model, the finite amount of resources available for the technological implementation of CO2 revalorizing processes arises as a central issue. The development of fully renewable catalytic systems with easier metal recovery strategies would promote the viability and sustainability of synthetic natural gas production circular routes. Taking Ni and NiFe catalysts supported over γ-Al2O3 oxide as reference materials, this work evaluates the potentiality of Ni and NiFe supported biochar catalysts for CO2 methanation. The development of competitive biochar catalysts was found dependent on the creation of basic sites on the catalyst surface. Displaying lower Turn Over Frequencies than Ni/Al catalyst, the absence of basic sites achieved over Ni/C catalyst was related to the depleted catalyst performances. For NiFe catalysts, analogous Ni5Fe1 alloys were constituted over both alumina and biochar supports. The highest specific activity of the catalyst series, exhibited by the NiFe/C catalyst, was related to the development of surface basic sites along with weaker NiFe–C interactions, which resulted in increased Ni0:NiO surface populations under reaction conditions. In summary, the present work establishes biochar supports as a competitive material to consider within the future low-carbon energetic panorama.
Mithilfe einer templatgestützten Synthese wurden poröse Kohlenstoffgerüste unter Verwendung von Silicagel als Templat hergestellt. Die chemische Gasphaseninfiltration (CVI) wurde hierbei als Synthese verwendet. Unter Variation verschiedener Reaktionsparameter zur Optimierung der Kohlenstoffabscheidung wurde dieser Prozess mathematisch modelliert and simuliert. Dabei konnten die experimentellen Ergebnisse gut mit den Modellen nachgebildet werden. Die zusätzliche Beschreibung der laminaren Strömung verbessert die Übereinstimmung deutlich.
This work analyses the catalytic activity displayed by Cu/SiO2, Cu-Fe/SiO2 and Cu/FSN (Fe-SiO2 nanocomposite) catalysts for the Reverse Water Gas Shift reaction. Compared to Cu/SiO2 catalyst, the presence of Fe resulted on higher CO’s selectivity and boosted resistances against the constitution of the deactivation carbonaceous species.
Regarding the catalytic performance however, the extent of improvement attained through incorporation Fe species strongly relied on the catalysts’ configuration. At 30 L/gh and H2:CO2 ratios = 3, the performance of the catalysts’ series increased according to the sequence: Cu/SiO2 < Cu-Fe/SiO2 << Cu/FSN. The remarkable catalytic
enhancements provided by Fe-SiO2 nanocomposites under different RWGS reaction atmospheres were associated to enhanced catalyst surface basicity’s and stronger Cu-support interactions. The catalytic promotion achieved by Fe-SiO2 nanocomposites argue an optimistic prospective for nanocomposite catalysts within future
CO2-valorising technologies.
Assessing the impact of textural properties in Ni–Fe catalysts for CO2 methanation performance
(2021)
In heterogeneous catalysis, the benefits of employing adequate textural properties on the catalytic performances are usually stated. Nevertheless, the quantification of the extent of improvement is not an easy task since variations on the catalysts’ specific areas and pore structures might involve modifications on a number of other
surface catalytic features. This study establishes the impact of the catalyst textural properties on the CO2 methanation performance by investigating bimetallic Ni–Fe catalysts supported over carbon supports with different textural properties regarding surface area and pore structure. The comparable metal loading and dispersions
attained for all systems enabled establishing forthright relationships between the catalyst textural properties and CO2 methanation rate. Once the influence of the external mass diffusions on the catalysts’ performance was experimentally discarded, the estimated Thiele modulus and internal effectiveness (φ and ηEff) values showed that the catalyst performance was majorly governed by the surface reaction rate whilst the pore size affected in no significant manner within the examined range (Dpore = 10.2 to 5.8 nm). Therefore, the rapport
between the catalyst performance and surface area was quantified for the CO2 methanation reaction over Ni–Fe catalysts: increasing the surface area from 572 to 802 m2/g permit obtaining ca. 10% higher CO2 conversions.
Hierarchically structured, porous carbon materials (PCM) were synthesized by sucrose infiltration into template material and subsequent carbonization. Three porous carbon materials were prepared using porous concrete (PCM-01) or silica gel (PCM-02 and 03) as template. Carbon particles from 125 to 200 μm were generated. Surface carboxylic group density was determined with 1.1 mmol/g dry material for each variant. Firstly, tailor-made PCM was evaluated as suitable support for lipase immobilization. Recombinant produced lipase of Thermomyces lanuginosus (TLL) was used as model enzyme. Two independent crude immobilization strategies were applied. Residual activities of up to 8.6 U/g and 31 U/g dry material for adsorptive and covalent immobilization (linkage via EDC) were achieved, respectively. Additionally, TLL was immobilized on commercially available polymethacrylate support showing similar residual lipase activities. Secondly, covalent immobilization was optimized to generate reproducible, highly stable and active immobilizates. Optimized covalent immobilizates showed residual activities of up to 10 U∙g⁻¹ dry carbon material using p-nitrophenyl-palmitate assay and protein loads of up to 45 mg g⁻¹dry carbon material. Covalent bound TLL-PCM showed storage stability for 12 months, remaining 100% of the initial activity. Operational stability resulted in stable and 100% active immobilizates over five consecutive cycles of use. Experiments showed that tailor-made porous carbon material is a promising support for lipase immobilization, which is adaptable in shape and dimension.
Zur Immobilisierung von Enzymen kann man Träger kaufen oder diese selbst herstellen. In früheren Arbeiten wurde ein Verfahren entwickelt, um hochporöse Kohlenstoffmaterialien in beliebigen Dimensionen herzustellen. Als Modell-Enzym zur Immobilisierung wurde die Thermomyces lanuginosus Lipase (TLL) gewählt, die adsorptiv und kovalent an das Material sowie an zwei käufliche Trägermaterialien
auf Polymethacryl-Basis (Funktionalitäten: Ethylendiamin- bzw. Diolgruppen)gebunden werden sollten. Es wurden Kohlenstoffgranulat (d = 125 –200 mm) und zylindrische Monolithe (h = 4 cm; d = 1 cm) synthetisiert. Die adsorptive Immobilisierung ergab am Kohlenstoffgranulat Aktivitäten von bis zu 2,5Ug⁻¹ gegenüber p-Nitrophenyl Palmitat (pNPP). Bei den zwei käuflichen Materialien
wurden Aktivitäten von bis zu 1,8Ug⁻¹ erreicht. Mit der kovalenten Immobilisierung konnten Aktivitäten von bis zu 10Ug⁻¹ am Kohlenstoffmaterial sowie dem Polymethacryl-Material (–OH funktionalisiert) gegenüber pNPP erreicht werden. Das Kohlenstoffmaterial ist ein geeigneter Träger für die TLL, der im Vergleich mit gängigen Materialien Aktivitäten in der gleichen Größenordnung zulässt. Das Porenvolumen des Materials sowie die
Makroporosität könnten erhöht werden, um Diffusions- und Durchströmungsbarrieren im Monolithen abzubauen.
Heterogeneously-Catalyzed Hydrogenation of Carbon Dioxide to Methane using RuNi Bimetallic Catalysts
(2015)
Control of porosity and composition of carbon based catalysts prepared by template assisted routes
(2015)
The potential of industrial porous concrete for using as a template for the synthesis of porous carbon materials has been investigated. Carbon replicas of porous concrete have been prepared by carbonization of sucrose. The pores of the resulting carbon materials range from the macropore to the micropore region, pointing to a hierarchy.