| 1. |
- Albertin, Stefano
(författare)
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Model catalysts studied by x-rays, visible and infrared light
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work is focused on the study of transition metal model catalysts for gas-phase heterogeneous catalysis, studied with light-based in-situ and operando techniques.Metallic model catalysts, such as Palladium (Pd) and Iridium (Ir) single crystals and in minor part deposited Rhodium (Rh), were studied using a combination of x-ray and non x-ray techniques. The aim was to either acquire structural characterization of new materials or pushing the state-of-the-art instrumental boundaries and close the material and pressure gap present in model catalysts studies. In this context were developed new techniques, such as Transmission Surface Diffraction (TSD), or further refined and validated, such as 2D Surface Optical Reflectance (2D-SOR).Pd, used in papers I,II , III , V , IX, was studied with a combination of X-ray Photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD) techniques as well as 2D-SOR and planar induced fluorescence (PLIF). This model catalyst was used as proof of concept for new approaches and new set-ups developed in collaboration with the combustion physics division, Lund University. One example is the use of the newly developed POLARIS High-Pressure XPS (HPXPS) station at P22 at PETRA III, Desy, Germany, demonstrating the potential and a new state-of-the-art of operando XPS. During this investigation, we have also confirmed Pd metallic islands' formation on PdO during reduction, a potentially critical factor in the modification and/or enhancement of the system catalytic activity. Another important result is obtained combining high energy surface X-ray Diffraction (HESXRD) with 2D-SOR and PLIF, and the characterization of 2D-SOR with an atomically precise diffraction method. During this investigation in particular we characterized the 2D-SOR sensitivity down to 2-3 Å by the observation of 2D-SOR signal from thin PdO (√5x√5)R27°.Similarly to Pd, in paper VI, we used Rh nanoparticles and films to implements a novel approach of Transmission Surface Diffraction (TSD) in which, at normal incidence angle, we performed diffraction in transmission through the sample with the use of high energy x-rays. With this contribution, we show that it is indeed possible to obtain reliable data in this configuration, contributing to mitigating the experimental challenges of experiments otherwise performed at grazing incidence geometry.Ir, used in papers VII, IX, VIII, was studied with XPS and XRD techniques to further understand the behavior of this, previously less investigated, catalyst that has recently gained popularity in both gas-heterogeneous as well as electrocatalysis community. XPS results provide further information on Ir metal and Ir oxide's reactivity and thermal stability while XRD results show the complex behavior of the catalyst under oxidation and reduction conditions. In particular, during the reduction it was observed the formation of Ir metallic islands on to ofIrO₂, in a parallel to the Pd/PdO/Pd case, and suggesting a possible general behavior for oxidized metal catalysts systems. The combination of these, both thermodynamic and structural data, provide new and much-needed information to the catalysis community, and at the same time, encourage a more well-defined approach to the IrO₂/Ir(100) system.
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| 2. |
- Albertin, Stefano, et al.
(författare)
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Oxidation and Reduction of Ir(100) Studied by High-Energy Surface X-ray Diffraction
- 2022
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:11, s. 5244-5255
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation and reduction of an Ir(100) surface using 2.5, 5, and 10 mbar O2 partial pressure and a sample temperature of 775 K have been studied by using high-energy surface X-ray diffraction (HESXRD) which allowed to record large volumes of reciprocal space in short time periods. The complex 3D diffraction patterns could be disentangled in a stepwise procedure. For the 2.5mbar experiment the measurements indicate the formation of an Ir(100)-O c(2 × 2) oxygen superstructure along with the onset of epitaxial IrO2(110) bulk oxide formation. For the 5 and 10 mbar O2 partial pressures the formation of additional IrO2 bulk oxide epitaxies with (100) and (101) orientations as well as of polycrystalline IrO2 was observed. Upon CO reduction, we found the IrO2 islands to be reduced into epitaxial and metallic Ir(111) and (221) oriented islands.
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| 3. |
- Blomberg, Sara, et al.
(författare)
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Bridging the Pressure Gap in CO Oxidation
- 2021
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 11:15, s. 9128-9135
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Tidskriftsartikel (refereegranskat)abstract
- Performing fundamental operando catalysis studies under realistic conditions is a key to further develop and increase the efficiency of industrial catalysts. Operando X-ray photoelectron spectroscopy (XPS) experiments have been limited to pressures, and the relevance for industrial applications has been questioned. Herein, we report on the CO oxidation experiment on Pd(100) performed at a total pressure of 1 bar using XPS. We investigate the light-off regime and the surface chemical composition at the atomistic level in the highly active phase. Furthermore, the observed gas-phase photoemission peaks of CO2, CO, and O2 indicate that the kinetics of the reaction during the light-off regime can be followed operando, and by studying the reaction rate of the reaction, the activation energy is calculated. The reaction was preceded by an in situ oxidation study in 7% O2 in He and a total pressure of 70 mbar to confirm the surface sensitivity and assignment of the oxygen-induced photoemission peaks. However, oxygen-induced photoemission peaks were not observed during the reaction studies, but instead, a metallic Pd phase is present in the highly active regime under the conditions applied. The novel XPS setup utilizes hard X-rays to enable high-pressure studies, combined with a grazing incident angle to increase the surface sensitivity of the measurement. Our findings demonstrate the possibilities of achieving chemical information of the catalyst, operando, on an atomistic level, under industrially relevant conditions.
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| 4. |
- Garcia-Martinez, Fernando, et al.
(författare)
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Reduced Carbon Monoxide Saturation Coverage on Vicinal Palladium Surfaces: The Importance of the Adsorption Site
- 2021
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:39, s. 9508-9515
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Tidskriftsartikel (refereegranskat)abstract
- Steps at metal surfaces may influence energetics and kinetics of catalytic reactions in unexpected ways. Here, we report a significant reduction of the CO saturation coverage in Pd vicinal surfaces, which in turn is relevant for the light-off of the CO oxidation reaction. The study is based on a systematic investigation of CO adsorption on vicinal Pd(111) surfaces making use of a curved Pd crystal. A combined X-ray Photoelectron Spectroscopy and DFT analysis allows us to demonstrate that an entire row of atomic sites under Pd steps remains free of CO upon saturation at 300 K, leading to a step-density-dependent reduction of CO coverage that correlates with the observed decrease of the light-off temperature during CO oxidation in vicinal Pd surfaces.
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| 5. |
- Goodwin, Christopher M., et al.
(författare)
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The Structure of the Active Pd State During Catalytic Carbon Monoxide Oxidization
- 2021
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:18, s. 4461-4465
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Tidskriftsartikel (refereegranskat)abstract
- Using grazing incidence X-rays and X-ray photoelectron spectroscopy during the mass transfer limited catalytic oxidation of CO, the long-range surface structure of Pd(100) was investigated. Under the reaction conditions of 50:4 O-2 to CO, 300 mbar pressure, and temperatures between 200 and 450 degrees C, the surface structure resulting from oxidation and the subsequent oxide reduction was elucidated. The reduction cycle was halted, and while under reaction conditions, angle-dependent X-ray photoelectron spectroscopy close to the critical angle of Pd and modeling of the data was performed. Two proposed models for the system were compared. The suggestion with the metallic islands formed on top of the oxide island was shown to be consistent with the data.
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| 6. |
- Martin, Rachel, et al.
(författare)
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Isothermal Reduction of IrO2 (110) Films by Methane Investigated Using In Situ X-ray Photoelectron Spectroscopy
- 2021
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 11:9, s. 5004-5016
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Tidskriftsartikel (refereegranskat)abstract
- Continuous exposure to methane causes IrO2 (110) films on Ir(100) to undergo extensive reduction at temperatures from 500 to 650 K. Measurements using in situ X-ray photoelectron spectroscopy (XPS) confirm that CH4 oxidation on IrO2 (110) converts so-called bridging oxygen atoms (O-br) at the surface to HObr groups while concurrently removing oxygen from the oxide film. Reduction of the IrO2 (110) film by methane is mildly activated as evidenced by an increase in the initial reduction rate as the temperature is increased from 500 to 650 K. The XPS results show that subsurface oxygen efficiently replaces O-br atoms at the IrO2 (110) surface during CH4 oxidation, even after the reduction of multiple layers of the oxide film, and that metallic Ir gradually forms at the surface as well. The isothermal rate of IrO2 (110) reduction by methane decreases continuously as metallic Ir replaces surface IrO2 (110) domains, demonstrating that IrO2 (110) is the active phase for CH4 oxidation under the conditions studied. A key finding is that the replacement of O-br atoms with oxygen from the subsurface is efficient enough to preserve IrO2 (110) domains at the surface and enable CH4 to reduce the similar to 10-layer IrO2 (110) films nearly to completion. In agreement with these observations, density functional theory calculations predict that oxygen atoms in the subsurface layer can replace O-br atoms at rates that are comparable to or higher than the rates at which O-br atoms are abstracted during CH4 oxidation. The efficacy with which oxygen in the bulk reservoir replenishes surface oxygen atoms has implications for understanding and modeling catalytic oxidation processes promoted by IrO2 (110).
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| 7. |
- Martin, Rachel, et al.
(författare)
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Methane oxidation on an IrO2(110) film
- 2019
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Ingår i: Abstracts of Papers of the American Chemical Society. - : American Chemical Society (ACS). - 0065-7727. ; 258
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Mehar, Vikram, et al.
(författare)
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Formation of Epitaxial PdO(100) During the Oxidation of Pd(100)
- 2023
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 14:38, s. 8493-8499
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The catalytic oxidation of CO and CH4 can be strongly influenced by the structures of oxide phases that form on metallic catalysts during reaction. Here, we show that an epitaxial PdO(100) structure forms at temperatures above 600 K during the oxidation of Pd(100) by gaseous O atoms as well as exposure to O2-rich mixtures at millibar partial pressures. The oxidation of Pd(100) by gaseous O atoms preferentially generates an epitaxial, multilayer PdO(101) structure at 500 K, but initiating Pd(100) oxidation above 600 K causes an epitaxial PdO(100) structure to grow concurrently with PdO(101) and produces a thicker and rougher oxide. We present evidence that this change in the oxidation behavior is caused by a temperature-induced change in the stability of small PdO domains that initiate oxidation. Our discovery of the epitaxial PdO(100) structure may be significant for developing relationships among oxide structure, catalytic activity, and reaction conditions for applications of oxidation catalysis.
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| 9. |
- Petrosino, Giuseppe, et al.
(författare)
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Identification of LINE retrotransposons and long non-coding RNAs expressed in the octopus brain
- 2022
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Ingår i: BMC Biology. - : BMC. - 1741-7007. ; 20:1
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Tidskriftsartikel (refereegranskat)abstract
- Background Transposable elements (TEs) widely contribute to the evolution of genomes allowing genomic innovations, generating germinal and somatic heterogeneity, and giving birth to long non-coding RNAs (lncRNAs). These features have been associated to the evolution, functioning, and complexity of the nervous system at such a level that somatic retrotransposition of long interspersed element (LINE) L1 has been proposed to be associated to human cognition. Among invertebrates, octopuses are fascinating animals whose nervous system reaches a high level of complexity achieving sophisticated cognitive abilities. The sequencing of the genome of the Octopus bimaculoides revealed a striking expansion of TEs which were proposed to have contributed to the evolution of its complex nervous system. We recently found a similar expansion also in the genome of Octopus vulgaris. However, a specific search for the existence and the transcription of full-length transpositionally competent TEs has not been performed in this genus. Results Here, we report the identification of LINE elements competent for retrotransposition in Octopus vulgaris and Octopus bimaculoides and show evidence suggesting that they might be transcribed and determine germline and somatic polymorphisms especially in the brain. Transcription and translation measured for one of these elements resulted in specific signals in neurons belonging to areas associated with behavioral plasticity. We also report the transcription of thousands of lncRNAs and the pervasive inclusion of TE fragments in the transcriptomes of both Octopus species, further testifying the crucial activity of TEs in the evolution of the octopus genomes. Conclusions The neural transcriptome of the octopus shows the transcription of thousands of putative lncRNAs and of a full-length LINE element belonging to the RTE class. We speculate that a convergent evolutionary process involving retrotransposons activity in the brain has been important for the evolution of sophisticated cognitive abilities in this genus.
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| 10. |
- Resta, Andrea, et al.
(författare)
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Ammonia Oxidation over a Pt25Rh75(001) Model Catalyst Surface : An Operando Study
- 2020
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:40, s. 22192-22199
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Tidskriftsartikel (refereegranskat)abstract
- The ammonia oxidation reaction over a PtRh binary alloy has been studied with a surface science approach by operando techniques such as near-ambient pressure X-ray photoemission spectroscopy (NAP-XPS) and surface X-ray diffraction (SXRD) combined with mass spectrometry. The article will explore the surface evolution across five different oxygen to ammonia ratios in the millibar regime for two different temperatures. The presented data set allows us to link variations in the atomic structures measured by diffraction methods and surface species information from NAP-XPS to reaction products in the gas phase. We will show that NO production coincides with significant changes of the surface structure and the formation of a RhO2 surface oxide. It was also observed that the RhO2 surface oxide only fully forms when the nitrogen signal in the N1s has disappeared.
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