Agnieszka Kierzkowska-Stürzlinger

Last Name

Kierzkowska-Stürzlinger

First Name

Agnieszka

ORCID

0000-0003-0828-1671

Organisational unit

03865 - Müller, Christoph R. / Müller, Christoph R.

Show all metadata

Search Results

Publications 1 - 10 of 15

Yolk-shell-type CaO-based sorbents for CO2 capture: assessing the role of nanostructuring for the stabilization of the cyclic CO2 uptake
Krödel, Maximilian; Oing, Alexander; Negele, Jan; et al. (2022)
Nanoscale
Engineering the Cu/Mo2CTx (MXene) interface to drive CO2 hydrogenation to methanol
Zhou, Hui; Chen, Zixuan; Vidal López, Anna; et al. (2021)
Nature Catalysis
Development of efficient catalysts for the direct hydrogenation of CO2 to methanol is essential for the valorization of this abundant feedstock. Here we show that a silica-supported Cu/Mo2CTx (MXene) catalyst achieves a higher intrinsic methanol formation rate per mass Cu than the reference Cu/SiO2 catalyst with a similar Cu loading. The Cu/Mo2CTx interface can be engineered due to the higher affinity of Cu for the partially reduced MXene surface (in preference to the SiO2 surface) and the mobility of Cu under H2 at 500 °C. With increasing reduction time, the Cu/Mo2CTx interface becomes more Lewis acidic due to the higher amount of Cu+ sites dispersed onto the reduced Mo2CTx and this correlates with an increased rate of CO2 hydrogenation to methanol. The critical role of the interface between Cu and Mo2CTx is further highlighted by density functional theory calculations that identify formate and methoxy species as stable reaction intermediates. [Figure not available: see fulltext.]
Structural Dynamics Behind the Formation of α′-Ni₃Ga Alloy Nanoparticles from a Ni–Ga Phyllosilicate Dispersed on Silica Using X-ray Probes
Zimmerli, Nora; Piankova, Diana; Kierzkowska-Stürzlinger, Agnieszka; et al. (2025)
Chemistry of Materials
This study investigates the structural evolution during the formation of α′-Ni₃Ga alloy nanoparticles from Ni–Ga phyllosilicate sheets upon heating in H₂. The phyllosilicate sheets were produced through a deposition–precipitation process using Ni and Ga nitrates and colloidal SiO₂. Advanced characterization techniques, including X-ray absorption spectroscopy, pair distribution function analysis, and electron microscopy, revealed the structure of the chrysotile-type phyllosilicates. Such phyllosilicates are composed of brucite-like layers with Ni²⁺ in octahedral coordination with oxygen (NiO₆), intercalated by layers of silica tetrahedra (SiO₄). Ga³⁺ ions partially replaced Ni²⁺ in octahedral positions within the brucite-like layers, but are also found in tetrahedral coordination, substituting Si⁴⁺ within the SiO₄ layers of the phyllosilicate phase and/or dispersed on/in the surface of the amorphous SiO₂ support. The structural transformation of the precursor material during thermal activation in H₂ was monitored by d-PDF and XAS. It was observed that the decomposition of the Ni–Ga phyllosilicate starts in the temperature range 290–310 °C, resulting in the formation of small nickel-rich nanoparticles and gallium oxide (GaOx) species. As the temperature is increased, Ga is reduced and is incorporated into the metallic nickel structure, ultimately forming intermetallic α′-Ni₃Ga nanoparticles with an average size of about 5 nm. Our findings provide a detailed mechanistic understanding of the structural evolution of the phyllosilicate-based precursor, including alloy/intermetallic formation under thermal reduction conditions and highlight the potential of mixed-metal phyllosilicates as precursors for bimetallic catalysts.
From ethene to propene (ETP) on tailored silica-alumina supports with isolated Ni(ii) sites: uncovering the importance of surface nickel aluminate sites and the carbon-pool mechanism
Chen, Zixuan; Docherty, Scott; Florian, Pierre; et al. (2022)
Catalysis Science & Technology
Catalysts with well-defined isolated Ni(ii) surface sites have been prepared on three silica-based supports. The outer shells of the support were comprised either of an amorphous aluminosilicate or amorphous alumina (AlOx) layer - associated with a high and low density of strong Bronsted acid sites (BAS), respectively. When tested for ethene-to-propene conversion, Ni catalysts with a higher density of strong BAS demonstrate a higher initial activity and productivity to propene. On all three catalysts, the propene productivity correlates closely with the concentration of C-8 aromatics, suggesting that propene may form via a carbon-pool mechanism. While all three catalysts deactivate with time on stream, the deactivation of catalysts with Ni(ii) sites on AlOx, i.e., containing surface Ni aluminate sites, is shown to be reversible by calcination (coke removal), in contrast to the deactivation of surface Ni silicate or aluminosilicate sites, which deactivate irreversibly by forming Ni nanoparticles.
Hydrogen dissociation sites on indium-based ZrO2-supported catalysts for hydrogenation of CO2 to methanol
Tsoukalou, Athanasia; Serykh, Alexander I.; Willinger, Elena; et al. (2022)
Catalysis Today
The formation and nature of surface indium species in zirconia-supported catalysts for the hydrogenation of CO2 to methanol has been investigated by infrared (IR) spectroscopy. We studied the dissociation of hydrogen on In2O3/m-ZrO2, In2O3/t-ZrO2, In2O3/am-ZrO2 and m-ZrO2:In catalysts (m-, t- and am- refers to monoclinic, tetragonal and amorphous, respectively and m-ZrO2:In is a solid solution material), with and without a redox pretreatment. Indium hydride species and hydroxyl groups form at room temperature on the surface of all redox-treated catalysts upon their exposure to hydrogen. The activity and concentration of surface indium sites capable of heterolytic activation of H2 is the highest in In2O3/m-ZrO2(redox). The sites for the dissociation of hydrogen also exist, although in lower concentration, on the surface of calcined In2O3/m-ZrO2 and m-ZrO2:In catalysts (evacuated at 400 °C), i.e. the catalysts featuring the highest activity in the hydrogenation of CO2 to methanol. Noteworthy, the room temperature reaction between CO2 and Insingle bondH species of redox-treated catalysts gave surface formate species, i.e. intermediates of the methanol synthesis pathway, only for In2O3/m-ZrO2(redox) and m-ZrO2:In(redox), highlighting more favourable reactivity of Insingle bondH species and carbonates on the m-ZrO2 support. In situ X-ray absorption spectroscopy (XAS) at the In K-edge demonstrates the transformation of In2O3/m-ZrO2, during reduction in H2 at 400 °C, into highly dispersed In sites with an average oxidation state between In2+ and In0. Subsequent oxidation recovers the In3+ oxidation state (in the in situ XAS experiment) and forms a m-ZrO2:In solid solution. Thus, H2 dissociation in the most active m-ZrO2:In catalyst proceeds on In3+–O–Zr4+ sites dispersed in m-ZrO2, forming In–H and Zr–OH sites.
Reversible transformation of sub-nanometer Ga-based clusters to isolated ^[4] Ga_(4Si) sites creates active centers for propane dehydrogenation
Chen, Zixuan; Serykh, Alexander I.; Kierzkowska-Stürzlinger, Agnieszka; et al. (2024)
Catalysis Science & Technology
Deciphering the structural dynamics in molten salt–promoted MgO-based CO2 sorbents and their role in the CO2 uptake
Rekhtina, Margarita; Krödel, Maximilian; Wu, Yi-Hsuan; et al. (2023)
Science Advances
The development of effective CO2 sorbents is vital to achieving net-zero CO2 emission targets. MgO promoted with molten salts is an emerging class of CO2 sorbents. However, the structural features that govern their performance remain elusive. Using in situ time-resolved powder x-ray diffraction, we follow the structural dynamics of a model NaNO3-promoted, MgO-based CO2 sorbent. During the first few cycles of CO2 capture and release, the sorbent deactivates owing to an increase in the sizes of the MgO crystallites, reducing in turn the abundance of available nucleation points, i.e., MgO surface defects, for MgCO3 growth. After the third cycle, the sorbent shows a continuous reactivation, which is linked to the in situ formation of Na2Mg(CO3)2 crystallites that act effectively as seeds for MgCO3 nucleation and growth. Na2Mg(CO3)2 forms due to the partial decomposition of NaNO3 during regeneration at T ≥ 450°C followed by carbonation in CO2.
Of Glasses and Crystals: Mitigating the Deactivation of CaO-Based CO₂ Sorbents through Calcium Aluminosilicates
Krödel, Maximilian; Leroy, César; Kim, Sung Min; et al. (2023)
JACS Au
CaO-based sorbents are cost-efficient materials for high-temperature CO₂ capture, yet they rapidly deactivate over carbonation-regeneration cycles due to sintering, hindering their utilization at the industrial scale. Morphological stabilizers such as Al₂O₃ or SiO₂ (e.g., introduced via impregnation) can improve sintering resistance, but the sorbents still deactivate through the formation of mixed oxide phases and phase segregation, rendering the stabilization inefficient. Here, we introduce a strategy to mitigate these deactivation mechanisms by applying (Al,Si)Oₓ overcoats via atomic layer deposition onto CaCO₃ nanoparticles and benchmark the CO₂ uptake of the resulting sorbent after 10 carbonation-regeneration cycles against sorbents with optimized overcoats of only alumina/silica (+25%) and unstabilized CaCO₃ nanoparticles (+55%). ²⁷Al and ²⁹Si NMR studies reveal that the improved CO₂ uptake and structural stability of sorbents with (Al,Si)Oₓ overcoats is linked to the formation of glassy calcium aluminosilicate phases (Ca,Al,Si)Oₓ that prevent sintering and phase segregation, probably due to a slower self-diffusion of cations in the glassy phases, reducing in turn the formation of CO₂ capture-inactive Ca-containing mixed oxides. This strategy provides a roadmap for the design of more efficient CaO-based sorbents using glassy stabilizers.
Correlating the Structural Evolution of ZnO/Al₂O₃ to Spinel Zinc Aluminate with its Catalytic Performance in Propane Dehydrogenation
Nadjafi, Manouchehr; Kierzkowska-Stürzlinger, Agnieszka; Armutlulu, Andac; et al. (2021)
The Journal of Physical Chemistry C
We correlate the catalytic activity for propane dehydrogenation (PDH) of a series of Zn-based Al2O3 catalysts with their structure and structural evolution. To this end, three model catalysts are investigated: (i) ZnO/Al2O3 prepared by atomic layer deposition (ALD) of ZnO onto γ-Al2O3 followed by calcination at 700 °C, which yields a core–shell spinel zinc aluminate/γ-Al2O3; (ii) zinc aluminate spinel nanoparticles (ZnxAlyO4 NPs) prepared via a hydrothermal method; and (iii) ZnO/SiO2 prepared by ALD of ZnO on SiO2. The catalysts are characterized by synchrotron X-ray powder diffraction (XRD), Zn K-edge X-ray absorption spectroscopy (XAS), and 27Al solid-state nuclear magnetic resonance (ssNMR). We identify tetrahedral Zn sites in close proximity to Al sites of a zinc aluminate spinel phase (ZnIV–O–AlIV/VI linkages) as more active and selective in PDH relative to the supported ZnO wurtzite phase (ZnIV–O– ZnIV linkages) in ZnO/SiO2. 50ZnO/Al2O3 gives 77% selectivity to propene at 9 mmol C3H6 gcat–1 h–1 space-time yield after 3 min of reaction at 600 °C. The ZnO/Al2O3 catalyst shows an irreversible loss of activity over repeated PDH and air-regeneration cycles attributed to Zn depletion on the surface, while the activity loss of ZnxAlyO4 NPs due to coke deposition can be recovered by air regeneration.
Structure of Na Species in Promoted CaO-Based Sorbents and Their Effect on the Rate and Extent of the CO2 Uptake
Krödel, Maximilian; Abduly, Lorenz; Nadjafi, Manouchehr; et al. (2023)
Advanced Functional Materials
To advance CaO-based CO₂ sorbents it is crucial to understand how their structural parameters control the cyclic CO₂ uptake. Here, CaO-based sorbents with varying ratios of Na₂CO₃:CaCO₃ are synthesized via mechanochemical activation of a mixture of Na₂CO₃ and CaCO₃ to investigate the effect of sodium species on the structure, morphology, carbonation rate and cyclic CO₂ uptake of the CO₂ sorbents. The addition of Na₂CO₃ in the range of 0.1–0.2 mol% improves the CO₂ uptake by up to 80% after 10 cycles when compared to ball-milled bare CaCO₃, while for Na₂CO₃ loadings >0.3 mol% the cyclic CO₂ uptake decreases by more than 40%. Energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy, X-ray absorption spectroscopy (XAS), and ²³Na MAS NMR, reveal that in sorbents with Na₂CO₃ contents <0.3 mol% Na exists in highly distributed, noncrystalline [Na₂Ca(CO₃)₂] units. These species stabilize the surface area of the sorbent in pores of diameters >100 nm, and enhance the diffusion of CO₂ through CaCO₃. For Na₂CO₃ contents >0.3 mol%, the accelerated deactivation of the sorbents via sintering is related to the formation of crystalline Na₂Ca(CO₃)₂ and the high mobility of Na.

Publications 1 - 10 of 15

Agnieszka Kierzkowska-Stürzlinger

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results