101
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Fernández S, Gao L, Hofmann JP, Carnis J, Labat S, Chahine GA, van Hoof AJF, Verhoeven MWGMT, Schülli TU, Hensen EJM, Thomas O, Richard MI. In situ structural evolution of single particle model catalysts under ambient pressure reaction conditions. NANOSCALE 2018; 11:331-338. [PMID: 30534681 DOI: 10.1039/c8nr08414a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The catalytic activity of metal nanoparticles can be altered by applying strain, which changes the crystalline lattice spacing and modifies the electronic properties of the metal. Understanding the role of elastic strain during catalytic reactions is thus crucial for catalyst design. Here, we show how single highly faceted Pt nanoparticles expand or contract upon interaction with different gas atmospheres using in situ nano-focused coherent X-ray diffraction imaging. We also demonstrate inter-particle heterogeneities, as they differ in development of strain under CO oxidation reaction conditions. The reported observations offer new insights into the design of catalysts exploiting strain effects.
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102
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Filonenko GA, Lugger JAM, Liu C, van Heeswijk EPA, Hendrix MMRM, Weber M, Müller C, Hensen EJM, Sijbesma RP, Pidko EA. Tracking Local Mechanical Impact in Heterogeneous Polymers with Direct Optical Imaging. Angew Chem Int Ed Engl 2018; 57:16385-16390. [PMID: 30182453 PMCID: PMC6348422 DOI: 10.1002/anie.201809108] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Indexed: 11/22/2022]
Abstract
Structural heterogeneity defines the properties of many functional polymers and it is often crucial for their performance and ability to withstand mechanical impact. Such heterogeneity, however, poses a tremendous challenge for characterization of these materials and limits our ability to design them rationally. Herein we present a practical methodology capable of resolving the complex mechanical behavior and tracking mechanical impact in discrete phases of segmented polyurethane-a typical example of a structurally complex polymer. Using direct optical imaging of photoluminescence produced by a small-molecule organometallic mechano-responsive sensor we observe in real time how polymer phases dissipate energy, restructure, and breakdown upon mechanical impact. Owing to its simplicity and robustness, this method has potential in describing the evolution of complex soft-matter systems for which global characterization techniques fall short of providing molecular-level insight.
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103
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Huang X, Ludenhoff JM, Dirks M, Ouyang X, Boot MD, Hensen EJM. Selective Production of Biobased Phenol from Lignocellulose-Derived Alkylmethoxyphenols. ACS Catal 2018; 8:11184-11190. [PMID: 30775063 PMCID: PMC6369661 DOI: 10.1021/acscatal.8b03430] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2018] [Revised: 10/08/2018] [Indexed: 11/29/2022]
Abstract
Lignocellulosic biomass is the only renewable source of carbon for the chemical industry. Alkylmethoxyphenols can be obtained in good yield from woody biomass by reductive fractionation, but these compounds are of limited value for large-scale applications. We present a method to convert lignocellulose-derived alkylmethoxyphenols to phenol that can be easily integrated in the petrochemical industry. The underlying chemistry combines demethoxylation catalyzed by a titania-supported gold nanoparticle catalyst and transalkylation of alkyl groups to a low-value benzene-rich stream promoted by HZSM-5 zeolite. In this way, phenol can be obtained in good yield, and benzene can be upgraded to more valuable propylbenzene, cumene, and toluene. We demonstrate that intimate contact between the two catalyst functions is crucial to transferring the methyl groups from the methoxy functionality to benzene instead of phenol. In a mixed-bed configuration, we achieved a yield of 60% phenol and 15% cresol from 4-propylguaiacol in a continuous one-step reaction at 350 °C at a weight hourly space velocity of ∼40 h-1.
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104
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van Hoof AJF, Filot IAW, Friedrich H, Hensen EJM. Reversible Restructuring of Silver Particles during Ethylene Epoxidation. ACS Catal 2018; 8:11794-11800. [PMID: 30555732 PMCID: PMC6292700 DOI: 10.1021/acscatal.8b03331] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Revised: 10/30/2018] [Indexed: 11/28/2022]
Abstract
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The restructuring
of a silver catalyst during ethylene epoxidation
under industrially relevant conditions was investigated without and
with vinyl chloride (VC) promotion. During non-VC-promoted ethylene
epoxidation, the silver particles grow and voids are formed at the
surface and in the bulk. Electron tomography highlighted the presence
of voids below the Ag surface. A mechanism is proposed involving reconstruction
of the silver lattice and defect sites induced by oxygen adsorption
on the external surface and grain boundaries, which finally create
pores. Promotion of the catalytic reaction by VC suppresses to a significant
extent void formation. The use of VC also redisperses silver particles,
initially grown during ethylene epoxidation without VC. This process
is rapid as the average size decreased from 172 to 136 nm within 2
h. These insights emphasize the dynamic nature of the silver particles
during the ongoing ethylene epoxidation reaction and indicate that
particle size and morphology strongly depend on reaction conditions.
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105
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Filonenko GA, Lugger JAM, Liu C, van Heeswijk EPA, Hendrix MMRM, Weber M, Müller C, Hensen EJM, Sijbesma RP, Pidko EA. Tracking Local Mechanical Impact in Heterogeneous Polymers with Direct Optical Imaging. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201809108] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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106
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Wang P, Chen W, Chiang FK, Dugulan AI, Song Y, Pestman R, Zhang K, Yao J, Feng B, Miao P, Xu W, Hensen EJM. Synthesis of stable and low-CO 2 selective ε-iron carbide Fischer-Tropsch catalysts. SCIENCE ADVANCES 2018; 4:eaau2947. [PMID: 30333996 PMCID: PMC6184692 DOI: 10.1126/sciadv.aau2947] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Accepted: 09/05/2018] [Indexed: 06/08/2023]
Abstract
The Fe-catalyzed Fischer-Tropsch (FT) reaction constitutes the core of the coal-to-liquids (CTL) process, which converts coal into liquid fuels. Conventional Fe-based catalysts typically convert 30% of the CO feed to CO2 in the FT unit. Decreasing the CO2 release in the FT step will reduce costs and enhance productivity of the overall process. In this context, we synthesize phase-pure ε(')-Fe2C catalysts exhibiting low CO2 selectivity by carefully controlling the pretreatment and carburization conditions. Kinetic data reveal that liquid fuels can be obtained free from primary CO2. These catalysts displayed stable FT performance at 23 bar and 235°C for at least 150 hours. Notably, in situ characterization emphasizes the high durability of pure ε(')-Fe2C in an industrial pilot test. These findings contribute to the development of new Fe-based FT catalysts for next-generation CTL processes.
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107
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Kosinov N, Uslamin EA, Coumans FJAG, Wijpkema ASG, Rohling RY, Hensen EJM. Structure and Evolution of Confined Carbon Species during Methane Dehydroaromatization over Mo/ZSM-5. ACS Catal 2018; 8:8459-8467. [PMID: 30271670 PMCID: PMC6156090 DOI: 10.1021/acscatal.8b02491] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Revised: 07/27/2018] [Indexed: 11/29/2022]
Abstract
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Surface carbon (coke, carbonaceous
deposits) is an integral aspect
of methane dehydroaromatization catalyzed by Mo/zeolites. We investigated
the evolution of surface carbon species from the beginning of the
induction period until the complete catalyst deactivation by the pulse
reaction technique, TGA, 13C NMR, TEM, and XPS. Isotope
labeling was performed to confirm the catalytic role of confined carbon
species during MDA. It was found that “hard” and “soft”
coke distinction is mainly related to the location of coke species
inside the pores and on the external surface, respectively. In addition,
MoO3 species act as an active oxidation catalyst, reducing
the combustion temperature of a certain fraction of coke. Furthermore,
after dissolving the zeolite framework by HF, we found that coke formed
during the MDA reaction inside the zeolite pores is essentially a
zeolite-templated carbon material. The possibility of preparing zeolite-templated
carbons from the most available hydrocarbon feedstock is important
for the development of these interesting materials.
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108
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Kouris PD, Huang X, Boot MD, Hensen EJM. Scaling-Up Catalytic Depolymerisation of Lignin: Performance Criteria for Industrial Operation. Top Catal 2018. [DOI: 10.1007/s11244-018-1048-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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109
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Wiesfeld JJ, Sommerdijk NAJM, Hensen EJM. Early Transition Metal Doped Tungstite as an Effective Catalyst for Glucose Upgrading to 5-Hydroxymethylfurfural. Catal Letters 2018. [DOI: 10.1007/s10562-018-2483-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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110
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Li G, Pidko EA, Hensen EJM, Nakajima K. A Density Functional Theory Study of the Mechanism of Direct Glucose Dehydration to 5-Hydroxymethylfurfural on Anatase Titania. ChemCatChem 2018. [DOI: 10.1002/cctc.201800900] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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111
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Yarulina I, De Wispelaere K, Bailleul S, Goetze J, Radersma M, Abou-Hamad E, Vollmer I, Goesten M, Mezari B, Hensen EJM, Martínez-Espín JS, Morten M, Mitchell S, Perez-Ramirez J, Olsbye U, Weckhuysen BM, Van Speybroeck V, Kapteijn F, Gascon J. Publisher Correction: Structure-performance descriptors and the role of Lewis acidity in the methanol-to-propylene process. Nat Chem 2018; 10:897. [PMID: 29991809 DOI: 10.1038/s41557-018-0118-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In the version of this Article originally published, on the right side of Fig. 4b, the 'Aromatic cycle' label was erroneously shifted outside of the central circular arrow into a position on part of the reaction cycle. This has been corrected in the online versions of the Article.
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112
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Su YQ, Liu JX, Filot IAW, Zhang L, Hensen EJM. Highly Active and Stable CH 4 Oxidation by Substitution of Ce 4+ by Two Pd 2+ Ions in CeO 2(111). ACS Catal 2018; 8:6552-6559. [PMID: 30023135 PMCID: PMC6046217 DOI: 10.1021/acscatal.8b01477] [Citation(s) in RCA: 66] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2018] [Revised: 05/27/2018] [Indexed: 11/28/2022]
Abstract
Methane (CH4) combustion is an increasingly important reaction for environmental protection, for which Pd/CeO2 has emerged as the preferred catalyst. There is a lack of understanding of the nature of the active site in these catalysts. Here, we use density functional theory to understand the role of doping of Pd in the ceria surface for generating sites highly active toward the C-H bonds in CH4. Specifically, we demonstrate that two Pd2+ ions can substitute one Ce4+ ion, resulting in a very stable structure containing a highly coordinated unsaturated Pd cation that can strongly adsorb CH4 and dissociate the first C-H bond with a low energy barrier. An important aspect of the high activity of the stabilized isolated Pd cation is its ability to form a strong σ-complex with CH4, which leads to effective activation of CH4. We show that also other transition metals like Pt, Rh, and Ni can give rise to similar structures with high activity toward C-H bond dissociation. These insights provide us with a novel structural view of solid solutions of transition metals such as Pt, Pd, Ni, and Rh in CeO2, known to exhibit high activity in CH4 combustion.
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113
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Rohling R, Tranca IC, Hensen EJM, Pidko EA. Electronic Structure Analysis of the Diels-Alder Cycloaddition Catalyzed by Alkali-Exchanged Faujasites. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2018; 122:14733-14743. [PMID: 30018699 PMCID: PMC6038092 DOI: 10.1021/acs.jpcc.8b04409] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Revised: 06/07/2018] [Indexed: 05/22/2023]
Abstract
The Diels-Alder cycloaddition (DAC) reaction is a commonly employed reaction for the formation of C-C bonds. DAC catalysis can be achieved by using Lewis acids and via reactant confinement in aqueous nanocages. Low-silica alkali-exchanged faujasite catalysts combine these two factors in one material. They can be used in the tandem DAC/dehydration reaction of biomass-derived 2,5-dimethylfuran (DMF) with ethylene toward p-xylene, in which the DAC reaction step initiates the overall reaction cycle. In this work, we performed periodic density functional theory (DFT) calculations on the DAC reaction between DMF and C2H4 in low-silica alkali(M)-exchanged faujasites (MY; Si/Al = 2.4; M = Li+, Na+, K+, Rb+, Cs+). The aim was to investigate how confinement of reactants in MY catalysts changed their electronic structure and the DAC-reactivity trend among the evaluated MY zeolites. The conventional high-silica alkali-exchanged isolated site model (MFAU; Si/Al = 47) served as a reference. The results show that confinement leads to initial-state (IS) destabilization and transition-state (TS) stabilization. Among the tested MY, most significant IS destabilization is found in RbY. Only antibonding orbital interactions between the reactants/reactive complex and cations were found, indicating that TS stabilization arises from ionic interactions. Additionally, in RbY the geometry of the transition state is geometrically most similar to that of the initial and final state. RbY also exhibits an optimal combination of the confinement-effects, resulting in having the lowest computed DAC-activation energy. The overall effect is a DAC-reactivity trend inversion in MY as compared to the trend found in MFAU where the activation energy correlates with the Lewis acidity of the exchangeable cations.
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114
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Kim M, Su Y, Fukuoka A, Hensen EJM, Nakajima K. Aerobic Oxidation of 5‐(Hydroxymethyl)furfural Cyclic Acetal Enables Selective Furan‐2,5‐dicarboxylic Acid Formation with CeO
2
‐Supported Gold Catalyst. Angew Chem Int Ed Engl 2018; 57:8235-8239. [DOI: 10.1002/anie.201805457] [Citation(s) in RCA: 111] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Indexed: 11/07/2022]
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115
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Kim M, Su Y, Fukuoka A, Hensen EJM, Nakajima K. Aerobic Oxidation of 5‐(Hydroxymethyl)furfural Cyclic Acetal Enables Selective Furan‐2,5‐dicarboxylic Acid Formation with CeO
2
‐Supported Gold Catalyst. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201805457] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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116
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Zhang Y, Gao L, Hensen EJM, Hofmann JP. Evaluating the Stability of Co 2P Electrocatalysts in the Hydrogen Evolution Reaction for Both Acidic and Alkaline Electrolytes. ACS ENERGY LETTERS 2018; 3:1360-1365. [PMID: 29911183 PMCID: PMC5996345 DOI: 10.1021/acsenergylett.8b00514] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Accepted: 05/16/2018] [Indexed: 05/22/2023]
Abstract
The evaluation of the stability of emerging earth-abundant metal phosphide electrocatalysts by solely electrochemical current-potential sweeps is often not conclusive. In this study, we investigated Co2P to evaluate its stability under both acidic (0.5 M H2SO4) and alkaline (1.0 M KOH) hydrogen evolution (HER) conditions. We found that the electrochemical surface area (ECSA) of Co2P only slightly increased in acidic conditions but almost doubled after electrolysis in alkaline electrolyte. The surface composition of the electrode remained almost unchanged in acid but was significantly altered in alkaline during current-potential sweeps. Analysis of the electrolytes after the stability test shows almost stoichiometric composition of Co and P in acid, but a preferential dissolution of P over Co could be observed in alkaline electrolyte. Applying comprehensive postcatalysis analysis of both the electrode and electrolyte, we conclude that Co2P, prepared by thermal phosphidization, dissolves stoichiometrically in acid and degrades to hydroxides under alkaline stability testing.
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117
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Kosinov N, Liu C, Hensen EJM, Pidko EA. Engineering of Transition Metal Catalysts Confined in Zeolites. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2018; 30:3177-3198. [PMID: 29861546 PMCID: PMC5973782 DOI: 10.1021/acs.chemmater.8b01311] [Citation(s) in RCA: 138] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Revised: 04/26/2018] [Indexed: 05/09/2023]
Abstract
Transition metal-zeolite composites are versatile catalytic materials for a wide range of industrial and lab-scale processes. Significant advances in fabrication and characterization of well-defined metal centers confined in zeolite matrixes have greatly expanded the library of available materials and, accordingly, their catalytic utility. In this review, we summarize recent developments in the field from the perspective of materials chemistry, focusing on synthesis, postsynthesis modification, (operando) spectroscopy characterization, and computational modeling of transition metal-zeolite catalysts.
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118
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Geonmonond RS, Quiroz J, Rocha GFSR, Oropeza FE, Rangel CJ, Rodrigues TS, Hofmann JP, Hensen EJM, Ando RA, Camargo PHC. Marrying SPR excitation and metal-support interactions: unravelling the contribution of active surface species in plasmonic catalysis. NANOSCALE 2018; 10:8560-8568. [PMID: 29694475 DOI: 10.1039/c8nr00934a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Plasmonic catalysis takes advantage of the surface plasmon resonance (SPR) excitation to drive or accelerate chemical transformations. In addition to the plasmonic component, the control over metal-support interactions in these catalysts is expected to strongly influence the performances. For example, CeO2 has been widely employed towards oxidation reactions due to its oxygen mobility and storage properties, which allow for the formation of Ce3+ sites and adsorbed oxygen species from metal-support interactions. It is anticipated that these species may be activated by the SPR excitation and contribute to the catalytic activity of the material. Thus, a clear understanding of the role played by the SPR-mediated activation of surface oxide species at the metal-support interface is needed in order to take advantage of this phenomenon. Herein, we describe and quantify the contribution from active surface oxide species at the metal-support interface (relative to O2 from air) to the activities in green SPR-mediated oxidation reactions. We employed CeO2 decorated with Au NPs (Au/CeO2) as a model plasmonic catalyst and the oxidation of p-aminothiophenol (PATP) and aniline as proof-of-concept transformations. We compared the results with SiO2 decorated with Au NPs (Au/SiO2), in which the formation of surface oxide species at the metal-support interface is not expected. We found that the SPR-mediated activation of surface oxide species at the metal-support interface in Au/CeO2 played a pivotal role in the detected activities, being even higher than the contribution coming from the activation of O2 from air.
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119
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Osadchii DY, Olivos-Suarez AI, Szécsényi Á, Li G, Nasalevich MA, Dugulan IA, Crespo PS, Hensen EJM, Veber SL, Fedin MV, Sankar G, Pidko EA, Gascon J. Isolated Fe Sites in Metal Organic Frameworks Catalyze the Direct Conversion of Methane to Methanol. ACS Catal 2018. [DOI: 10.1021/acscatal.8b00505] [Citation(s) in RCA: 145] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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120
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Broos RP, Zijlstra B, Filot IAW, Hensen EJM. Quantum-Chemical DFT Study of Direct and H- and C-Assisted CO Dissociation on the χ-Fe 5C 2 Hägg Carbide. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2018; 122:9929-9938. [PMID: 29774085 PMCID: PMC5949720 DOI: 10.1021/acs.jpcc.8b01064] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Revised: 03/15/2018] [Indexed: 06/08/2023]
Abstract
The first step in the Fischer-Tropsch reaction is the production of C1 monomers by the dissociation of the C-O bond. Although Fe is the active metal, it is well known that under typical reaction conditions, it changes into various carbide phases. The Hägg carbide (χ-Fe5C2) phase is usually considered as the catalytically active phase. We carried out a comprehensive DFT study of CO dissociation on various surface terminations of the Hägg carbide, selected on their specific site topology and the presence of stepped sites. Based on the reaction energetics, we identified several feasible CO dissociation pathways over the Hägg carbide. In this study, we have compared the direct CO dissociation with H- and C-assisted CO dissociation mechanisms. We demonstrated that the reaction rate for CO dissociation critically depends on the presence and topology of interstitial C atoms close to the active site. Typically, the CO dissociation proceeds via a direct C-O bond scission mechanism on the stepped sites on the Fe carbide surface. We have shown a preference for the direct CO dissociation on the surfaces with a stepped character. The H-assisted CO dissociation, via a CHO intermediate, was preferred when the surface did not have a clear stepped character. We have also shown that activation barriers for dissociation are highly dependent on the surface termination. With a consistent data set and including migration corrections, we then compared the CO dissociation rates based on a simplified kinetic model. With this model, we showed that besides the activation energy, the adsorption energy of the CO, the C and the O species are important for the reaction rate as well. We found that the most active surface termination is a (111̅) surface cut in such a way that the surface exposes B5 sites that are not occupied by the C atoms. On these B5 sites, the direct CO dissociation presents the highest rate.
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121
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Liu JX, Filot IAW, Su Y, Zijlstra B, Hensen EJM. Optimum Particle Size for Gold-Catalyzed CO Oxidation. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2018; 122:8327-8340. [PMID: 29707098 PMCID: PMC5911800 DOI: 10.1021/acs.jpcc.7b12711] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2017] [Revised: 02/28/2018] [Indexed: 05/28/2023]
Abstract
The structure sensitivity of gold-catalyzed CO oxidation is presented by analyzing in detail the dependence of CO oxidation rate on particle size. Clusters with less than 14 gold atoms adopt a planar structure, whereas larger ones adopt a three-dimensional structure. The CO and O2 adsorption properties depend strongly on particle structure and size. All of the reaction barriers relevant to CO oxidation display linear scaling relationships with CO and O2 binding strengths as main reactivity descriptors. Planar and three-dimensional gold clusters exhibit different linear scaling relationship due to different surface topologies and different coordination numbers of the surface atoms. On the basis of these linear scaling relationships, first-principles microkinetics simulations were conducted to determine CO oxidation rates and possible rate-determining step of Au particles. Planar Au9 and three-dimensional Au79 clusters present the highest CO oxidation rates for planar and three-dimensional clusters, respectively. The planar Au9 cluster is much more active than the optimum Au79 cluster. A common feature of optimum CO oxidation performance is the intermediate binding strengths of CO and O2, resulting in intermediate coverages of CO, O2, and O. Both these optimum particles present lower performance than maximum Sabatier performance, indicating that there is sufficient room for improvement of gold catalysts for CO oxidation.
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122
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Liu JX, Su Y, Filot IAW, Hensen EJM. A Linear Scaling Relation for CO Oxidation on CeO 2-Supported Pd. J Am Chem Soc 2018; 140:4580-4587. [PMID: 29498273 PMCID: PMC5890314 DOI: 10.1021/jacs.7b13624] [Citation(s) in RCA: 77] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2017] [Indexed: 11/28/2022]
Abstract
Resolving the structure and composition of supported nanoparticles under reaction conditions remains a challenge in heterogeneous catalysis. Advanced configurational sampling methods at the density functional theory level are used to identify stable structures of a Pd8 cluster on ceria (CeO2) in the absence and presence of O2. A Monte Carlo method in the Gibbs ensemble predicts Pd-oxide particles to be stable on CeO2 during CO oxidation. Computed potential energy diagrams for CO oxidation reaction cycles are used as input for microkinetics simulations. Pd-oxide exhibits a much higher CO oxidation activity than metallic Pd on CeO2. This work presents for the first time a scaling relation for a CeO2-supported metal nanoparticle catalyst in CO oxidation: a higher oxidation degree of the Pd cluster weakens CO binding and facilitates the rate-determining CO oxidation step with a ceria O atom. Our approach provides a new strategy to model supported nanoparticle catalysts.
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123
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Richard MI, Fernández S, Eymery J, Hofmann JP, Gao L, Carnis J, Labat S, Favre-Nicolin V, Hensen EJM, Thomas O, Schülli TU, Leake SJ. Crystallographic orientation of facets and planar defects in functional nanostructures elucidated by nano-focused coherent diffractive X-ray imaging. NANOSCALE 2018; 10:4833-4840. [PMID: 29473085 DOI: 10.1039/c7nr07990g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The physical and chemical properties of nanostructures depend on their surface facets. Here, we exploit a pole figure approach to determine the three-dimensional orientation matrix of a nanostructure from a single Bragg reflection measured with a coherent nano-focused X-ray beam. The signature of any truncated (faceted) crystal produces a crystal truncation rod, which corresponds to a streak of intensity in reciprocal space normal to the surface. When two or more non-parallel facets are present, both the crystal orientation and the crystal facets can be identified. This enables facets to be rapidly indexed and uncommon facets, and planar defects, that have been difficult to study before to be identified. We demonstrate the technique with (i) epitaxial core-shell InGaN/GaN multiple quantum-wells grown on GaN nanowires, where surface facets and planar defects are determined, and (ii) single randomly oriented highly faceted tetrahedrahexal Pt nanoparticles. The methodology is applicable to a broad range of nanocrystals and provides a unique insight into the connection between structure and properties of nanomaterials.
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124
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Goryachev A, Gao L, Zhang Y, Rohling RY, Vervuurt RHJ, Bol AA, Hofmann JP, Hensen EJM. Stability of CoP x Electrocatalysts in Continuous and Interrupted Acidic Electrolysis of Water. ChemElectroChem 2018; 5:1230-1239. [PMID: 29732273 PMCID: PMC5915747 DOI: 10.1002/celc.201701119] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Indexed: 11/29/2022]
Abstract
Cobalt phosphides are an emerging earth‐abundant alternative to platinum‐group‐metal‐based electrocatalysts for the hydrogen evolution reaction (HER). Yet, their stability is inferior to platinum and compromises the large‐scale applicability of CoPx in water electrolyzers. In the present study, we employed flat, thin CoPx electrodes prepared through the thermal phosphidation (PH3) of Co3O4 films made by plasma‐enhanced atomic layer deposition to evaluate their stability in acidic water electrolysis by using a multi‐technique approach. The films were found to be composed of two phases: CoP in the bulk and a P‐rich surface CoPx (P/Co>1). Their performance was evaluated in the HER and the exchange current density was determined to be j0=−8.9 ⋅ 10−5 A/cm2. The apparent activation energy of HER on CoPx (Ea=81±15 kJ/mol) was determined for the first time. Dissolution of the material in 0.5 M H2SO4 was observed, regardless of the constantly applied cathodic potential, pointing towards a chemical instead of an electrochemical origin of the observed cathodic instability. The current density and HER faradaic efficiency (FE) were found to be stable during chronoamperometric treatment, as the chemical composition of the HER‐active phase remained unchanged. On the contrary, a dynamic potential change performed in a repeated way facilitated dissolution of the film, yielding its complete degradation within 5 h. There, the FE was also found to be changing. An oxidative route of CoPx dissolution has also been proposed.
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Liu K, Huang X, Pidko EA, Hensen EJM. Hydrogenation of Lactic Acid to 1,2-Propanediol over Ru-Based Catalysts. ChemCatChem 2018; 10:810-817. [PMID: 29541255 PMCID: PMC5838540 DOI: 10.1002/cctc.201701329] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Revised: 09/25/2017] [Indexed: 11/16/2022]
Abstract
The catalytic hydrogenation of lactic acid to 1,2-propanediol with supported Ru catalysts in water was investigated. The influence of catalyst support (activated carbon, γ-Al2O3, SiO2, TiO2, and CeO2) and promoters (Pd, Au, Mo, Re, Sn) on the catalytic performance was evaluated. Catalytic tests revealed that TiO2 yields the best Ru catalysts. With a monometallic Ru/TiO2 catalyst, a 1,2-propanediol yield of 70 % at 79 % lactic acid conversion was achieved at 130 °C after 20 h reaction. Minor byproducts of the hydrogenation reaction were propionic acid, ethanol, 1-propanol, and 2-propanol. For the bimetallic catalysts, the addition of Pd and Au slightly enhanced the performance of Ru/TiO2, whereas the addition of common hydrogenation promoters such as Re, Mo, and Sn impaired the activity.
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