Active Pt-Nanocoated Layer with Pt–O–Ce Bonds on a CeOx Nanowire Cathode Formed by Electron Beam Irradiation
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ABSTRACT:
SUBMITTER: Mori T
PROVIDER: S-EPMC9330286 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Multiply bonded lanthanide oxo groups are rare in coordination compounds and have not previously been reported for a surface termination of a lanthanide oxide. Here we report the observation of a Ce=O terminated ceria surface in a CeO2 (111)-( 3 × 3 )R30° reconstruction of ≈3 nm thick ceria islands prepared on Pt(111). This is evidenced by scanning tunnelling microscopy (STM), low energy electron diffraction (LEED) and high-resolution electron energy loss spectroscopy (HREELS) measurements in conjunction with density functional theory (DFT) calculations. A Ce=O stretching frequency of 775 cm-1 is observed in HREELS, compared with 766 cm-1 calculated by DFT. The calculations also predict that the Ce=O bond is weak, with an oxygen vacancy formation energy of 0.85 eV. This could play an important role in the facile removal of lattice oxygen from CeO2 , accompanied by the reduction of CeIV to CeIII , which is a key attribute of ceria-based systems in connection with their unique catalytic properties.
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Project description:The design of Pt-based nanoarchitectures with controllable compositions and morphologies is necessary to enhance their electrocatalytic activity. Herein, we report a rational design and synthesis of anisotropic mesoporous Pt@Pt-skin Pt3Ni core-shell framework nanowires for high-efficient electrocatalysis. The catalyst has a uniform core-shell structure with an ultrathin atomic-jagged Pt nanowire core and a mesoporous Pt-skin Pt3Ni framework shell, possessing high electrocatalytic activity, stability and Pt utilisation efficiency. For the oxygen reduction reaction, the anisotropic mesoporous Pt@Pt-skin Pt3Ni core-shell framework nanowires demonstrated exceptional mass and specific activities of 6.69 A/mgpt and 8.42 mA/cm2 (at 0.9 V versus reversible hydrogen electrode), and the catalyst exhibited high stability with negligible activity decay after 50,000 cycles. The mesoporous Pt@Pt-skin Pt3Ni core-shell framework nanowire configuration combines the advantages of three-dimensional open mesopore molecular accessibility and compressive Pt-skin surface strains, which results in more catalytically active sites and weakened chemisorption of oxygenated species, thus boosting its catalytic activity and stability towards electrocatalysis.
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Project description:The addition of platinum-group metals (PGMs, e.g., Pt) to CeO2 is used in heterogeneous catalysis to promote the rate of redox surface reactions. Well-defined model system studies have shown that PGMs facilitate H2 dissociation, H-spillover onto CeO2 surfaces, and CeO2 surface reduction. However, it remains unclear how the heterogeneous structures and interfaces that exist on powder catalysts influence the mechanistic picture of PGM-promoted H2 reactions on CeO2 surfaces developed from model system studies. Here, controlled catalyst synthesis, temperature-programmed reduction (TPR), in situ infrared spectroscopy (IR), and in situ electron energy loss spectroscopy (EELS) were used to interrogate the mechanisms of how Pt nanoclusters and single atoms influence H2 reactions on high-surface area Pt/CeO2 powder catalysts. TPR showed that Pt promotes H2 consumption rates on Pt/CeO2 even when Pt exists on a small fraction of CeO2 particles, suggesting that H-spillover proceeds far from Pt-CeO2 interfaces and across CeO2-CeO2 particle interfaces. IR and EELS measurements provided evidence that Pt changes the mechanism of H2 activation and the rate limiting step for Ce3+, oxygen vacancy, and water formation as compared to pure CeO2. As a result, higher-saturation surface hydroxyl coverages can be achieved on Pt/CeO2 compared to pure CeO2. Further, Ce3+ formed by spillover-H from Pt is heterogeneously distributed and localized at and around interparticle CeO2-CeO2 boundaries, while activated H2 on pure CeO2 results in homogeneously distributed Ce3+. Ce3+ localization at and around CeO2-CeO2 boundaries for Pt/CeO2 is accompanied by surface reconstruction that enables faster rates of H2 consumption. This study reconciles the materials gap between model structures and powder catalysts for H2 reactions with Pt/CeO2 and highlights how the spatial heterogeneity of powder catalysts dictates the influence of Pt on H2 reactions at CeO2 surfaces.
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Project description:The hydrogen-borrowing amination of alcohols is a promising route to produce amines. In this study, experimental parameters involved in the preparation of Pt/CeO2 catalysts were varied to assess how physicochemical properties influence their performance in such reactions. An amination reaction between cyclopentanol and cyclopentylamine was used as the model reaction for this study. The Pt precursor used in the catalyst synthesis and the properties of the CeO2 support were both found to strongly influence catalytic performance. Aberration corrected scanning transmission electron microscopy revealed that the most active catalyst comprised linearly structured Pt species. The formation of these features, a function result of epitaxial Pt deposition along the CeO2 [100] plane, appeared to be dependent on the properties of the CeO2 support and the Pt precursor used. Density functional theory calculations subsequently confirmed that these sites were more effective for cyclopentanol dehydrogenation-considered to be the rate-determining step of the process-than Pt clusters and nanoparticles. This study provides insights into the desirable catalytic properties required for hydrogen-borrowing amination but has relevance to other related fields. We consider that this study will provide a foundation for further study in this atom-efficient area of chemistry.
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Project description:Supported Pt-based catalysts have been identified as highly selective catalysts for CO oxidation, but their potential for applications has been hampered by the high cost and scarcity of Pt metals as well as aggregation problems at relatively high temperatures. In this work, nanorod structured (TiO2-Pt)/CeO2 catalysts with the addition of 0.3 at% Pt and different atomic ratios of Ti were prepared through a combined dealloying and calcination method. XRD, XPS, SEM, TEM, and STEM measurements were used to confirm the phase composition, surface morphology, and structure of synthesized samples. After calcination treatment, Pt nanoparticles were semi-inlayed on the surface of the CeO2 nanorod, and TiO2 was highly dispersed into the catalyst system, resulting in the formation of (TiO2-Pt)/CeO2 with high specific surface area and large pore volume. The unique structure can provide more reaction path and active sites for catalytic CO oxidation, thus contributing to the generation of catalysts with high catalytic activity. The outstanding catalytic performance is ascribed to the stable structure and proper TiO2 doping as well as the combined effect of Pt, TiO2, and CeO2. The research results are of importance for further development of high catalytic performance nanoporous catalytic materials.
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Project description:In the current context of complexity between climate change, environmental sustainability, resource scarcity, and geopolitical aspects of energy resources, a polygenerative system with a circular approach is considered to generate energy (thermal, electrical, and fuel), contributing to the control of CO2 emissions. A plant for the multiple productions of electrical energy, thermal heat, DME, syngas, and methanol is discussed and analyzed, integrating a chemical cycle for CO2/H2O splitting driven using concentrated solar energy and biomethane. Two-stage chemical looping is the central part of the plant, operating with the CeO2/Ce2O3 redox couple and operating at 1.2 bar and 900 °C. The system is coupled to biomethane reforming. The chemical loop generates fuel for the plant's secondary units: a DME synthesis and distillation unit and a solid oxide fuel cell (SOFC). The DME synthesis and distillation unit are integrated with a biomethane reforming reactor powered by concentrated solar energy to produce syngas at 800 °C. The technical feasibility in terms of performance is presented in this paper, both with and without solar irradiation, with the following results, respectively: overall efficiencies of 62.56% and 59.08%, electricity production of 6.17 MWe and 28.96 MWe, and heat production of 111.97 MWt and 35.82 MWt. The fuel production, which occurs only at high irradiance, is 0.71 kg/s methanol, 6.18 kg/s DME, and 19.68 kg/s for the syngas. The increase in plant productivity is studied by decoupling the operation of the chemical looping with a biomethane reformer from intermittent solar energy using the heat from the SOFC unit.
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Project description:Low temperature CO oxidation reaction is known to be facilitated over platinum supported on a reducible cerium oxide. Pt species act as binding sites for reactant CO molecules, and oxygen vacancies on surface of cerium oxide atomically activate the reactant O2 molecules. However, the impacts of size of Pt species and concentration of oxygen vacancy at the surface of cerium oxide on the CO oxidation reaction have not been clearly distinguished, thereby various diverse approaches have been suggested to date. Here using the co-precipitation method we have prepared pure ceria support and infiltrated it with Pt solution to obtain 0.5 atomic% Pt supported on cerium oxide catalyst, and then systematically varied the size of Pt from single atom to ∼1.7 nm sized nanoparticles and oxygen vacancy concentration at surface of cerium oxide by controlling the heat-treatment conditions, which are temperature and oxygen partial pressure. It is found that Pt nanoparticles in range of 1-1.7 nm achieve 100% of CO oxidation reaction at ∼100 °C lower temperature compared to Pt single atom owing to the facile adsorption of CO but weaker binding strength between Pt and CO molecules, and the oxygen vacancy in the vicinity of Pt accelerates CO oxidation below 150 °C. Based on this understanding, we show that a simple hydrogen reduction at 550 °C for the single atom Pt supported on CeO2 catalyst induces the formation of highly dispersed Pt nanoparticles with size of 1.7 ± 0.2 nm and the higher concentration of surface oxygen vacancies simultaneously, enabling 100% conversion from CO to CO2 at 200 °C as well as 16% conversion even at 150 °C owing to the synergistic effects of Pt nanoparticles and oxygen vacancies.
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Project description:The development of Ce-based materials is directly dependent on the catalyst surface defects, which is caused by the calcination steps required to increase structural stability. At the same time, the evaluation of cerium's redox properties under reaction conditions is of increasing relevant importance. The synthesis of Ce-UiO-66 and CeZr-UiO-66 and their subsequent calcination are presented here as a simple and inexpensive approach for achieving homogeneous and stable CeO2 and CeZrOx nanocrystals. The resulting materials constitute an ideal case study to thoroughly understand cerium redox properties. The Ce3+/Ce4+ redox properties are investigated by H2-TPR experiments exploited by in situ FT-IR and Ce M5-edge AP-NEXAFS spectroscopy. In the latter case, Ce3+ formation is quantified using the MCR-ALS protocol. FT-IR is then presented as a high potential/easily accessible technique for extracting valuable information about the cerium oxidation state under operating conditions. The dependence of the OH stretching vibration frequency on temperature and Ce reduction is described, providing a novel tool for qualitative monitoring of surface oxygen vacancy formation. Based on the reported results, the molecular absorption coefficient of the Ce3+ characteristic IR transition is tentatively evaluated, thus providing a basis for future Ce3+ quantification through FT-IR spectroscopy. Finally, the FT-IR limitations for Ce3+ quantification are discussed.
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Project description:Two platinum precursors, Pt(CO)2Cl2 and Pt(CO)2Br2, were designed for focused electron beam-induced deposition (FEBID) with the aim of producing platinum deposits of higher purity than those deposited from commercially available precursors. In this work, we present the first deposition experiments in a scanning electron microscope (SEM), wherein series of pillars were successfully grown from both precursors. The growth of the pillars was studied as a function of the electron dose and compared to deposits grown from the commercially available precursor MeCpPtMe3. The composition of the deposits was determined using energy-dispersive X-ray spectroscopy (EDX) and compared to the composition of deposits from MeCpPtMe3, as well as deposits made in an ultrahigh-vacuum (UHV) environment. A slight increase in metal content and a higher growth rate are achieved in the SEM for deposits from Pt(CO)2Cl2 compared to MeCpPtMe3. However, deposits made from Pt(CO)2Br2 show slightly less metal content and a lower growth rate compared to MeCpPtMe3. With both Pt(CO)2Cl2 and Pt(CO)2Br2, a marked difference in composition was found between deposits made in the SEM and deposits made in UHV. In addition to Pt, the UHV deposits contained halogen species and little or no carbon, while the SEM deposits contained only small amounts of halogen species but high carbon content. Results from this study highlight the effect that deposition conditions can have on the composition of deposits created by FEBID.
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Project description:The formation of cerianite (CeO2) was investigated at low hydrothermal conditions (35-205 °C) via two experimental settings: (1) crystallisation from solution experiments, and (2) replacement of Ca-Mg carbonates (calcite, dolomite, aragonite) mediated by Ce-bearing aqueous solutions. The solid samples were studied with a combination of powder X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The results revealed a multi-step crystallisation pathway: amorphous Ce carbonate → Ce-lanthanite [Ce2(CO3)3·8H2O] → Ce-kozoite [orthorhombic CeCO3(OH)] → Ce-hydroxylbastnasite [hexagonal CeCO3(OH)] → cerianite [CeO2]. We found that Ce carbonates can decarbonise in the final stage of the reaction, forming cerianite which significantly increases the porosity of the solids. The redox behaviour of Ce combined with the temperature, and the availability of CO2 3- govern this crystallisation sequence, the sizes, morphologies, and crystallisation mechanisms of the solid phases. Our results explain the occurrence and behaviour of cerianite in natural deposits. These findings also present a simple, environmental-friendly, and cost-efficient method for the synthesis of Ce carbonates and cerianite with tailored structures and chemistries.
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