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Stable mass-selected AuTiO x nanoparticles for CO oxidation. Phys Chem Chem Phys 2024; 26:9253-9263. [PMID: 38445363 DOI: 10.1039/d4cp00211c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2024]
Abstract
Stability under reactive conditions poses a common challenge for cluster- and nanoparticle-based catalysts. Since the catalytic properties of <5 nm gold nanoparticles were first uncovered, optimizing their stability at elevated temperatures for CO oxidation has been a central theme. Here we report direct observations of improved stability of AuTiOx alloy nanoparticles for CO oxidation compared with pure Au nanoparticles on TiO2. The nanoparticles were synthesized using a magnetron sputtering, gas-phase aggregation cluster source, size-selected using a lateral time-of-flight mass filter and deposited onto TiO2-coated micro-reactors for thermocatalytic activity measurements of CO oxidation. The AuTiOx nanoparticles exhibited improved stability at elevated temperatures, which is attributed to a self-anchoring interaction with the TiO2 substrate. The structure of the AuTiOx nanoparticles was also investigated in detail using ion scattering spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The measurements showed that the alloyed nanoparticles exhibited a core-shell structure with an Au core surrounded by an AuTiOx shell. The structure of these alloy nanoparticles appeared stable even at temperatures up to 320 °C under reactive conditions, for more than 140 hours. The work presented confirms the possibility of tuning catalytic activity and stability via nanoparticle alloying and self-anchoring on TiO2 substrates, and highlights the importance of complementary characterization techniques to investigate and optimize nanoparticle catalyst designs of this nature.
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Systematic Investigation on Supported Gold Catalysts Prepared by Fluorine-Free Basic Etching Ti 3AlC 2 in Selective Oxidation of Aromatic Alcohols to Aldehydes. MATERIALS (BASEL, SWITZERLAND) 2023; 16:3139. [PMID: 37109976 PMCID: PMC10143880 DOI: 10.3390/ma16083139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/19/2023] [Revised: 04/06/2023] [Accepted: 04/12/2023] [Indexed: 06/19/2023]
Abstract
Conventional methods to prepare supported metal catalysts are chemical reduction and wet impregnation. This study developed and systematically investigated a novel reduction method based on simultaneous Ti3AlC2 fluorine-free etching and metal deposition to prepare gold catalysts. The new series of Aupre/Ti3AlxC2Ty catalysts were characterized by XRD, XPS, TEM, and SEM and were tested in the selective oxidation of representative aromatic alcohols to aldehydes. The catalytic results demonstrate the effectiveness of the preparation method and better catalytic performances of Aupre/Ti3AlxC2Ty, compared with those of catalysts prepared by traditional methods. Moreover, this work presents a comprehensive study on the influence of calcination in air, H2, and Ar, and we found that the catalyst of Aupre/Ti3AlxC2Ty-Air600 obtained by calcination in air at 600 °C performed the best, owing to the synergistic effect between tiny surface TiO2 species and Au NPs. The tests of reusability and hot filtration confirmed the catalyst stability.
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A Tale of Two Sites: Neighboring Atomically Dispersed Pt Sites Cooperatively Remove Trace H 2 in CO-Rich Stream. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2204611. [PMID: 36257908 DOI: 10.1002/smll.202204611] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2022] [Revised: 08/29/2022] [Indexed: 06/16/2023]
Abstract
Single-atom catalysts (SACs) exhibit distinct catalytic behavior compared with nano-catalysts because of their unique atomic coordination environment without the direct bonding between identical metal centers. How these single atom sites interact with each other and influence the catalytic performance remains unveiled as designing densely populated but stable SACs is still an enormous challenge to date. Here, a fabrication strategy for embedding high areal density single-atom Pt sites via a defect engineering approach is demonstrated. Similar to the synergistic mechanism in binuclear homogeneous catalysts, from both experimental and theoretical results, it is proved that electrons would redistribute between the two oxo-bridged paired Pt sites after hydrogen adsorption on one site, which enables the other Pt site to have high CO oxidation activity at mild-temperature. The dynamic electronic interaction between neighboring Pt sites is found to be distance dependent. These new SACs with abundant Pt-O-Pt paired structures can improve the efficiency of CO chemical purification.
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The different evolution behaviors of carbonate-like species on Pt/CeO2 and Pt/Al2O3 by in situ DRIFTS-MS study. Catal Today 2022. [DOI: 10.1016/j.cattod.2021.11.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Operando Spectroscopic Study of the Dynamics of Ru Catalyst during Preferential Oxidation of CO and the Prevention of Ammonia Poisoning by Pt. JACS AU 2022; 2:1627-1637. [PMID: 35911446 PMCID: PMC9326823 DOI: 10.1021/jacsau.2c00195] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Hydrogen is a promising clean energy source. In domestic polymer electrolyte fuel cell systems, hydrogen is produced by reforming of natural gas; however, the reformate contains carbon monoxide (CO) as a major impurity. This CO is removed from the reformate by a combination of the water-gas shift reaction and preferential oxidation of CO (PROX). Currently, Ru-based catalysts are the most common type of PROX catalyst; however, their durability against ammonia (NH3) as an impurity produced in situ from trace amounts of nitrogen also contained in the reformate is an important issue. Previously, we found that addition of Pt to an Ru catalyst inhibited deactivation by NH3. Here, we conducted operando XAFS and FT-IR spectroscopic analyses with simultaneous gas analysis to investigate the cause of the deactivation of an Ru-based PROX catalyst (Ru/α-Al2O3) by NH3 and the mechanism of suppression of the deactivation by adding Pt (Pt/Ru/α-Al2O3). We found that nitric oxide (NO) produced by oxidation of NH3 induces oxidation of the Ru nanoparticle surface, which deactivates the catalyst via a three-step process: First, NO directly adsorbs on Ru0 to form NO-Ruδ+, which then induces the formation of O-Ru n+ by oxidation of the surrounding Ru0. Then, O-Ru m+ is formed by oxidation of Ru0 starting from the O-Ru n+ nuclei and spreading across the surface of the nanoparticle. Pt inhibits this process by alloying with Ru and inducing the decomposition of adsorbed NO, which keeps the Ru in a metallic state.
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Abstract
Hydrogen (H2) has emerged as a sustainable energy carrier capable of replacing/complementing the global carbon-based energy matrix. Although studies in this area have often focused on the fundamental understanding of catalytic processes and the demonstration of their activities towards different strategies, much effort is still needed to develop high-performance technologies and advanced materials to accomplish widespread utilization. The main goal of this review is to discuss the recent contributions in the H2 production field by employing nanomaterials with well-defined and controllable physicochemical features. Nanoengineering approaches at the sub-nano or atomic scale are especially interesting, as they allow us to unravel how activity varies as a function of these parameters (shape, size, composition, structure, electronic, and support interaction) and obtain insights into structure–performance relationships in the field of H2 production, allowing not only the optimization of performances but also enabling the rational design of nanocatalysts with desired activities and selectivity for H2 production. Herein, we start with a brief description of preparing such materials, emphasizing the importance of accomplishing the physicochemical control of nanostructures. The review finally culminates in the leading technologies for H2 production, identifying the promising applications of controlled nanomaterials.
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Achieving acetone efficient deep decomposition by strengthening reactants adsorption and activation over difunctional Au(OH)K x/hierarchical MFI catalyst. J Colloid Interface Sci 2022; 612:504-515. [PMID: 35007876 DOI: 10.1016/j.jcis.2021.12.184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 12/16/2021] [Accepted: 12/29/2021] [Indexed: 11/23/2022]
Abstract
Realizing the simultaneous adsorption and activation of O2 and reactants over supported noble metal catalysts is crucial for the oxidation of organic hydrocarbons. Herein, we report a facile one-step ethylene glycol reduction method to synthesize difunctional Au(OH)Kx sites, which were anchored on a hierarchical hollow MFI support and adopted for acetone decomposition. The alkali ion-associated adjacent surface hydroxyl groups were coordinated with Au nanoparticles, resulting in partially oxidized Au1+ sites with improved dispersion. The results obtained from exclusive ex situ and in situ experiments illustrated that the proper content of K and hydroxyl groups significantly enhanced the adsorption of surface O2 and acetone molecules around the Au sites simultaneously, whereas the excess K species inhibited the catalytic performance by blocking the pore structure and decreasing the acidity of catalysts. The Au(OH)K0.7/h-MFI catalyst exhibited the highest efficiency for acetone oxidation, over which 1500 ppm acetone can be completely oxidized at just 280 °C with an extremely low activation energy of 32.5 kJ mol-1. The carbonate species were detected as the main intermediates during acetone decomposition over the difunctional Au(OH)Kx sites through a Langmuir - Hinshelwood (L - H) mechanism. This finding paves the way for designing and constructing efficient functional active sites for the complete oxidation of hydrocarbons.
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Low-Temperature Heterogeneous Oxidation Catalysis and Molecular Oxygen Activation. CATALYSIS REVIEWS 2021. [DOI: 10.1080/01614940.2021.1919044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Active Sites and Interfacial Reducibility of Cu xO/CeO 2 Catalysts Induced by Reducing Media and O 2/H 2 Activation. ACS APPLIED MATERIALS & INTERFACES 2021; 13:35804-35817. [PMID: 34313106 DOI: 10.1021/acsami.1c09332] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The development of a highly efficient and stable catalyst for preferential oxidation of CO for the commercialization of proton-exchange membrane fuel cells has been a result of continuous effort. The main challenge is the simultaneous control of abundant active sites and interfacial reducibility over the catalyst CuxO/CeO2. Here, we report a strategy to modulate porosity, active sites, and O-vacancy sites (OV) by reducing media and O2/H2 activation. O2-pretreated CeO2-supported Cu catalysts unequivocally demonstrate the low-temperature activity owing to the excess concentrations of Cu+ and Cu2+ as well as the relative population of Ce3+ and O-vacancy sites at the surface. O2 activation improves the Cu2+ diffusion into the CeO2 lattice to generate the synergistic effect and induces the formation of electron-enriched Cu2+-OV-Ce3+ sites, which accelerate the activation and dissociation of CO/O2 and the formation of reactive oxygen species during catalysis. Density function theory (DFT) calculations reveal that CO adsorbs on Cu2O {110} and CuO {111} with relatively optimal adsorption energy and longer C-Cu lengths in contrast to that on Cu {111}, favoring the adsorption and desorption of CO. These are crucial for ongoing CO oxidation, producing CO2 by the Mars-van Krevelen mechanism.
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Toward an Atomic-Level Understanding of Ceria-Based Catalysts: When Experiment and Theory Go Hand in Hand. Acc Chem Res 2021; 54:2884-2893. [PMID: 34137246 PMCID: PMC8264949 DOI: 10.1021/acs.accounts.1c00226] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
ConspectusBecause ceria (CeO2) is a key ingredient in the formulation of many catalysts, its catalytic roles have received a great amount of attention from experiment and theory. Its primary function is to enhance the oxidation activity of catalysts, which is largely governed by the low activation barrier for creating lattice O vacancies. Such an important characteristic of ceria has been exploited in CO oxidation, methane partial oxidation, volatile organic compound oxidation, and the water-gas shift (WGS) reaction and in the context of automotive applications. A great challenge of such heterogeneously catalyzed processes remains the unambiguous identification of active sites.In oxidation reactions, closing the catalytic cycle requires ceria reoxidation by gas-phase oxygen, which includes oxygen adsorption and activation. While the general mechanistic framework of such processes is accepted, only very recently has an atomic-level understanding of oxygen activation on ceria powders been achieved by combined experimental and theoretical studies using in situ multiwavelength Raman spectroscopy and DFT.Recent studies have revealed that the adsorption and activation of gas-phase oxygen on ceria is strongly facet-dependent and involves different superoxide/peroxide species, which can now be unambiguously assigned to ceria surface sites using the combined Raman and DFT approach. Our results demonstrate that, as a result of oxygen dissociation, vacant ceria lattice sites are healed, highlighting the close relationship of surface processes with lattice oxygen dynamics, which is also of technical relevance in the context of oxygen storage-release applications.A recent DFT interpretation of Raman spectra of polycrystalline ceria enables us to take account of all (sub)surface and bulk vibrational features observed in the experimental spectra and has revealed new findings of great relevance for a mechanistic understanding of ceria-based catalysts. These include the identification of surface oxygen (Ce-O) modes and the quantification of subsurface oxygen defects. Combining these theoretical insights with operando Raman experiments now allows the (sub)surface oxygen dynamics of ceria and noble metal/ceria catalysts to be monitored under the reaction conditions.Applying these findings to Au/ceria catalysts provides univocal evidence for ceria support participation in heterogeneous catalysis. For room-temperature CO oxidation, operando Raman monitoring the (sub)surface defect dynamics clearly demonstrates the dependence of catalytic activity on the ceria reduction state. Extending the combined experimental/DFT approach to operando IR spectroscopy allows the elucidation of the nature of the active gold as (pseudo)single Au+ sites and enables us to develop a detailed mechanistic picture of the catalytic cycle. Temperature-dependent studies highlight the importance of facet-dependent defect formation energies and adsorbate stabilities (e.g., carbonates). While the latter aspects are also evidenced to play a role in the WGS reaction, the facet-dependent catalytic performance shows a correlation with the extent of gold agglomeration. Our findings are fully consistent with a redox mechanism, thus adding a new perspective to the ongoing discussion of the WGS reaction.As outlined above for ceria-based catalysts, closely combining state-of-the-art in situ/operando spectroscopy and theory constitutes a powerful approach to rational catalyst design by providing essential mechanistic information based on an atomic-level understanding of reactions.
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Fundamental Aspects of Ceria Supported Au Catalysts Probed by In Situ/Operando Spectroscopy and TAP Reactor Studies. Chemphyschem 2021; 22:1302-1315. [PMID: 33908151 PMCID: PMC8362095 DOI: 10.1002/cphc.202100027] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 04/17/2021] [Indexed: 11/30/2022]
Abstract
The discovery of the activity of dispersed gold nanoparticles three decades ago paved the way for a new era in catalysis. The unusual behavior of these catalysts sparked many questions about their working mechanism. In particular, Au/CeO2 proved to be an efficient catalyst in several reactions such as CO oxidation, water gas shift, and CO2 reduction. Here, by employing findings from operando X‐ray absorption spectroscopy at the near and extended Au and Ce LIII energy edges, we focus on the fundamental aspects of highly active Au/CeO2 catalysts, mainly in the CO oxidation for understanding their complex structure‐reactivity relationship. These results were combined with findings from in situ diffuse reflectance FTIR and Raman spectroscopy, highlighting the changes of adlayer and ceria defects. For a comprehensive understanding, the spectroscopic findings will be supplemented by results of the dynamics of O2 activation obtained from Temporal Analysis of Products (TAP). Merging these results illuminates the complex relationship among the oxidation state, size of the Au nanoparticles, the redox properties of CeO2 support, and the dynamics of O2 activation.
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Influence of hematite morphology on the CO oxidation performance of Au/α-Fe2O3. CHINESE JOURNAL OF CATALYSIS 2021. [DOI: 10.1016/s1872-2067(20)63687-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Au/La-CeO catalyst for CO oxidation: Effect of different atmospheres pretreatment on gold state ― Commemorating the 100th anniversary of the birth of Academician Guangxian Xu. J RARE EARTH 2021. [DOI: 10.1016/j.jre.2021.01.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Insight into the mechanism of the water-gas shift reaction over Au/CeO 2 catalysts using combined operando spectroscopies. Faraday Discuss 2021; 229:232-250. [PMID: 33634801 DOI: 10.1039/c9fd00133f] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The mechanism of the low-temperature water-gas shift (LT-WGS) reaction over Au/CeO2 catalysts with different ceria terminations, i.e., (111), (110), and (100) facets, was investigated. Using combined operando Raman and UV-Vis spectroscopy as well as isotope exchange experiments, we are able to draw conclusions about the reducibility behaviour and the exchange of surface oxygen. Additional density functional theory (DFT) calculations facilitate the vibrational bands assignments and enhance the interpretation of the results on a molecular level. A facet-dependent role of gold is observed with respect to the oxygen dynamics, since for the CeO2(111) facet the presence of gold is required to exchange surface oxygen, whereas the CeO2(110) facet requires no gold, as rationalized by the low defect formation energy of this facet. This behaviour suggests that surface properties (termination, stepped surface) may have a strong effect on the reactivity. While the reduction of the support accompanies the reaction, its extent does not directly correlate with activity, highlighting the importance of other properties, such as the dissociative adsorption of water and/or CO2/H2 desorption. The results of our facet-dependent study are consistent with a redox mechanism, as underlined by H218O isotopic exchange experiments demonstrating the ready exchange of surface oxygen.
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Ultrastable titania-supported Au nanoparticles covered by chromia via photo-induced strategy for low-temperature CO oxidation. CATAL COMMUN 2021. [DOI: 10.1016/j.catcom.2020.106199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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19
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FTIR investigation under reaction conditions during CO oxidation over Ru(x)-CeO2 catalysts. MOLECULAR CATALYSIS 2020. [DOI: 10.1016/j.mcat.2020.111086] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Au-Decorated Ce-Ti Mixed Oxides for Efficient CO Preferential Photooxidation. ACS APPLIED MATERIALS & INTERFACES 2020; 12:38019-38030. [PMID: 32687700 PMCID: PMC7458359 DOI: 10.1021/acsami.0c08258] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Accepted: 07/20/2020] [Indexed: 06/11/2023]
Abstract
We investigated the photocatalytic behavior of gold nanoparticles supported on CeO2-TiO2 nanostructured matrixes in the CO preferential oxidation in H2-rich stream (photo-CO-PROX), by modifying the electronic band structure of ceria through addition of titania and making it more suitable for interacting with free electrons excited in gold nanoparticles through surface plasmon resonance. CeO2 samples with different TiO2 concentrations (0-20 wt %) were prepared through a slow coprecipitation method in alkaline conditions. The synthetic route is surfactant-free and environmentally friendly. Au nanoparticles (<1.0 wt % loading) were deposited on the surface of the CeO2-TiO2 oxides by deposition-precipitation. A benchmarking sample was also considered, prepared by standard fast coprecipitation, to assess how a peculiar morphology can affect the photocatalytic behavior. The samples appeared organized in a hierarchical needle-like structure, with different morphologies depending on the Ti content and preparation method, with homogeneously distributed Au nanoparticles decorating the Ce-Ti mixed oxides. The morphology influences the preferential photooxidation of CO to CO2 in excess of H2 under simulated solar light irradiation at room temperature and atmospheric pressure. The Au/CeO2-TiO2 systems exhibit much higher activity compared to a benchmark sample with a non-organized structure. The most efficient sample exhibited CO conversions of 52.9 and 80.2%, and CO2 selectivities equal to 95.3 and 59.4%, in the dark and under simulated sunlight, respectively. A clear morphology-functionality correlation was found in our systematic analysis, with CO conversion maximized for a TiO2 content equal to 15 wt %. The outcomes of this study are significant advancements toward the development of an effective strategy for exploitation of hydrogen as a viable clean fuel in stationary, automotive, and portable power generators.
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Dual-Component Sodium and Cesium Promoters for Au/TS-1: Enhancement of Propene Epoxidation with Hydrogen and Oxygen. Ind Eng Chem Res 2020. [DOI: 10.1021/acs.iecr.9b07011] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Influence of gold on the reactivity behaviour of ceria nanorods in CO oxidation: combining operando spectroscopies and DFT calculations. Catal Sci Technol 2020. [DOI: 10.1039/d0cy00392a] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In this combined Raman/UV-Vis and DFT study, structure-activity relations for CO oxidation over ceria nanorods (with/without gold) with CeO2(110) and CeO2(100) termination are elucidated using ceria nanocubes with CeO2(100) termination as reference.
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Recent advances in synergistic effect promoted catalysts for preferential oxidation of carbon monoxide. Catal Sci Technol 2020. [DOI: 10.1039/c9cy02073j] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We reviewed recent advances in catalysts for PROX with emphasis on synergistic effects that contribute to enhanced catalytic performance.
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Importance of Size and Contact Structure of Gold Nanoparticles for the Genesis of Unique Catalytic Processes. Chem Rev 2019; 120:464-525. [DOI: 10.1021/acs.chemrev.9b00551] [Citation(s) in RCA: 249] [Impact Index Per Article: 49.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Chemical and Electronic Changes of the CeO2 Support during CO Oxidation on Au/CeO2 Catalysts: Time-Resolved Operando XAS at the Ce LIII Edge. Catalysts 2019. [DOI: 10.3390/catal9100785] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
While being highly active for the CO oxidation reaction already at low temperatures, Au/CeO2 catalysts suffer from continuous deactivation with time on stream, with the activity and deactivation depending on the initial catalyst activation procedure. In previous X-ray absorption measurements at the Au LIII edge, which focused on changes in the electronic and geometric changes of Au, we found a modest increase of the Au particle size during reaction, with the Au nanoparticles (NPs) present in a dominantly metallic state during reaction, regardless of the pretreatment. Here we aim at expanding on these insights by examining the changes in electronic and chemical composition of the CeO2 support induced by different pretreatment procedures and during subsequent CO oxidation at 80 °C, by following changes at the Ce LIII near edge region in time-resolved operando X-ray absorption measurements. The results indicate a strong dependence of the initial concentration of Ce3+ ions on the pretreatment, while during subsequent reaction this rapidly approaches a steady-state value which depends on the oxidative/reductive character of the reaction gas mixture, but is largely independent of the pretreatment. These results are discussed and related to earlier finding on the electronic properties of Au nanoparticles under identical reaction conditions.
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Influence of the Hydrothermal Parameters on the Physicochemical Characteristics of Cu−Ce Oxide Nanostructures. ChemCatChem 2019. [DOI: 10.1002/cctc.201901108] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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CeO 2 supported low-loading Au as an enhanced catalyst for low temperature oxidation of carbon monoxide. CrystEngComm 2019. [DOI: 10.1039/c9ce01301f] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
A series of low loading and high activity Au/CeO2 supported catalysts were synthesized using a coprecipitation method. Au/CeO2 catalysts with a low Au content (0.2 wt%) showed extremely high activity for CO oxidation with 100% conversion of CO around 60 °C.
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Comparison of Au–Ce and Au–Cu interaction over Au/CeO2–CuO catalysts for preferential CO oxidation. CrystEngComm 2019. [DOI: 10.1039/c8ce01839a] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Au decelerates reduction of copper species, while it improves ceria reduction.
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Enhancement of the activity and durability in CO oxidation over silica-supported Au nanoparticle catalyst via CeO modification. CHINESE JOURNAL OF CATALYSIS 2018. [DOI: 10.1016/s1872-2067(18)63136-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Understanding the preferential oxidation of carbon monoxide (PrOx) using size-controlled Au nanocrystal catalyst. AIChE J 2018. [DOI: 10.1002/aic.16206] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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Sustainable photo-assisted CO oxidation in H 2 -rich stream by simulated solar light response of Au nanoparticles supported on TiO 2. Catal Today 2018. [DOI: 10.1016/j.cattod.2017.09.048] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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Tailored metastable Ce-Zr oxides with highly distorted lattice oxygen for accelerating redox cycles. Chem Sci 2018; 9:3386-3394. [PMID: 29780469 PMCID: PMC5933218 DOI: 10.1039/c8sc00729b] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Accepted: 02/28/2018] [Indexed: 11/21/2022] Open
Abstract
Ceria-based catalysts are widely used in oxidation or oxidation-reduction reactions in the field of environmental science. Their catalytic functions are determined by their ability to exchange oxygen species with oxidants. The enhancement of oxygen release is desired since it is often the rate-determining step in redox cycles. Herein, we developed a lattice oxygen distortion method to enhance oxygen activation by quenching the Ce-Zr oxide nanoparticles formed from an extremely high temperature. This process can ensure the formation of solid solutions as well as avoiding atomic rearrangement during calcination, retaining the lattice oxygen at a metastable and disordered state without vacancies. Reduction, vacuum or metal deposition will easily induce oxygen release accompanied by vacancy creation. The metastable oxides can provide about 19 times more oxygen vacancies than traditional ones in a CO atmosphere. CO oxidation rates increased with increasing Zr content from 25 to 75% and achieved a new level, which is attributed to the acceleration of oxygen circulation via promoting oxygen release and supplying plenty of oxygen vacancies for redox cycles. This strategy is expected to be applied in the design and fabrication of improved oxygen storage materials.
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Black TiO2−x with stable surface oxygen vacancies as the support of efficient gold catalysts for water-gas shift reaction. Catal Sci Technol 2018. [DOI: 10.1039/c7cy02429k] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
H2-etching engineered oxygen vacancies on black TiO2−x to enhance the hot-electron flow and water-gas shift catalytic performance of Au catalysts.
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The Solid-State-Grinding Synthesis of Maganese-Modified Cobalt Oxides and Application in the Low-Temperature CO Preferential Oxidation in H2-Rich Gases. CATALYSIS SURVEYS FROM ASIA 2017. [DOI: 10.1007/s10563-017-9235-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Boosting Cu-Ce interaction in Cu x O/CeO 2 nanocube catalysts for enhanced catalytic performance of preferential oxidation of CO in H 2 -rich gases. MOLECULAR CATALYSIS 2017. [DOI: 10.1016/j.mcat.2017.04.013] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Influence of Chitosan on the Microstructured Au/CeO2 Catalyst: An Enhanced Catalytic Performance for CO Oxidation. Catal Letters 2017. [DOI: 10.1007/s10562-017-2039-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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The catalytic performance of Cu n Au (n = 3–12) clusters for preferential oxidation of CO in hydrogen-rich stream. Theor Chem Acc 2017. [DOI: 10.1007/s00214-017-2062-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Enhanced catalytic activities and selectivities in preferential oxidation of CO over ceria-promoted Au/Al 2 O 3 catalysts. CHINESE JOURNAL OF CATALYSIS 2016. [DOI: 10.1016/s1872-2067(16)62469-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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39
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CO Oxidation on Ceria Supported Gold Catalysts Studied by Combined Operando Raman/UV–Vis and IR Spectroscopy. Top Catal 2016. [DOI: 10.1007/s11244-016-0732-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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40
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Copper-Modified Gold Nanoparticles as Highly Selective Catalysts for Glycerol Electro-Oxidation in Alkaline Solution. ChemCatChem 2016. [DOI: 10.1002/cctc.201600725] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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Deactivation of Au/CeO2 catalysts during CO oxidation: Influence of pretreatment and reaction conditions. J Catal 2016. [DOI: 10.1016/j.jcat.2016.07.005] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Abstract
Au deposition on CeO2 support is oxygen vacancies dependent. Optimized VOs result in small gold particle size and positively charged Auδ+ to promote CO oxidation; excess VOs lead to agglomerated Au NPs and the reduction of Au3+ reactive species, with catalysis deactivation.
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Anchoring High-Concentration Oxygen Vacancies at Interfaces of CeO(2-x)/Cu toward Enhanced Activity for Preferential CO Oxidation. ACS APPLIED MATERIALS & INTERFACES 2015; 7:22999-3007. [PMID: 26444246 DOI: 10.1021/acsami.5b06302] [Citation(s) in RCA: 88] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Catalysts are urgently needed to remove the residual CO in hydrogen feeds through selective oxidation for large-scale applications of hydrogen proton exchange membrane fuel cells. We herein propose a new methodology that anchors high concentration oxygen vacancies at interface by designing a CeO2-x/Cu hybrid catalyst with enhanced preferential CO oxidation activity. This hybrid catalyst, with more than 6.1% oxygen vacancies fixed at the favorable interfacial sites, displays nearly 100% CO conversion efficiency in H2-rich streams over a broad temperature window from 120 to 210 °C, strikingly 5-fold wider than that of conventional CeO2/Cu (i.e., CeO2 supported on Cu) catalyst. Moreover, the catalyst exhibits a highest cycling stability ever reported, showing no deterioration after five cycling tests, and a super long-time stability beyond 100 h in the simulated operation environment that involves CO2 and H2O. On the basis of an arsenal of characterization techniques, we clearly show that the anchored oxygen vacancies are generated as a consequence of electron donation from metal copper atoms to CeO2 acceptor and the subsequent reverse spillover of oxygen induced by electron transfer in well controlled nanoheterojunction. The anchored oxygen vacancies play a bridging role in electron capture or transfer and drive molecule oxygen into active oxygen species to interact with the CO molecules adsorbed at interfaces, thus leading to an excellent preferential CO oxidation performance. This study opens a window to design a vast number of high-performance metal-oxide hybrid catalysts via the concept of anchoring oxygen vacancies at interfaces.
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Highly Efficient Catalysis of Preferential Oxidation of CO in H2-Rich Stream by Gold Single-Atom Catalysts. ACS Catal 2015. [DOI: 10.1021/acscatal.5b01114] [Citation(s) in RCA: 309] [Impact Index Per Article: 34.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Nanogold supported on manganese oxide doped alumina microspheres as a highly active and selective catalyst for CO oxidation in a H2-rich stream. Chem Commun (Camb) 2015; 51:17728-31. [DOI: 10.1039/c5cc06480e] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The exceptionally high catalytic activity for CO-PROX reaction is due to the Au–support interaction and the unique reducibility of the support.
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