Metal-Free Low-Temperature Water–Gas Shift Catalysis over Small, Hydroxylated Ceria Nanoparticles

Xing, Huaizhong; Beck, Matthew J.

doi:10.1021/acscatal.5b01227

Cited by 14 publications

(9 citation statements)

References 53 publications

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“…A practical example of this type of process is the reaction of CO (= Z) with OH (= X) on a ceria surface, relevant to, that is, water–gas shift or preferential CO oxidation catalysis. − When the carboxyl (COOH) reaction product is considered to be adsorbed on Ce sites, the change in reaction energy upon OH pairing with H adsorbed on an oxygen site is equal to the difference in the pairing energy of COOHH and OHH pairs. Using the HSE06 functional, the COOHH pairing is calculated to be significantly weaker than the OHH pairing (−0.42 versus −1.66 eV).…”

Section: Resultsmentioning

confidence: 99%

Adsorbate Pairing on Oxide Surfaces: Influence on Reactivity and Dependence on Oxide, Adsorbate Pair, and Density Functional

Bossche

Grönbeck

2017

J. Phys. Chem. C

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Open-shell molecules on metal oxide surfaces frequently display cooperative adsorption mechanisms, where pairs of adsorbates are significantly more stable than the isolated species. In this work, density functional theory is used to investigate the cooperative adsorption of OHH and NO2NO on rocksalt BaO(100), rutile TiO2(110), fluorite CeO2(111), and tetragonal PdO(101) surfaces. The OH and NO2 adsorbates are considered to be located at the metal sites, whereas H and NO are situated on the oxygen sites. Despite differences in adsorption mechanisms, the pairing is found to be consistently exothermic. The pairing is most pronounced on BaO(100) and weakest on PdO(101). OH and H form more stable pairs than do NO2 and NO. In all cases except CeO2(111), the hybrid HSE06 functional predicts a stronger pairing than the semilocal PBE functional. The absolute pairing energy is a convoluted measure of charge transfer energies, electrostatic interactions, and ionic relaxations, which is analyzed in detail using a thermodynamic cycle. Adsorbate pairing has marked effects on the reactivity, which is exemplified by studying the reaction of CO with OH on CeO2(111).

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Section: Resultsmentioning

confidence: 99%

Adsorbate Pairing on Oxide Surfaces: Influence on Reactivity and Dependence on Oxide, Adsorbate Pair, and Density Functional

Bossche

Grönbeck

2017

J. Phys. Chem. C

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“…The metals adsorb and activate CO, while the ceria serves to dissociate water . Nanostructured “metal‐free” ceria, especially sub‐10 nm nanoparticles, has recently become an interest for fundamental studies of the water‐gas shift reaction over the oxide . Herein we present a combined experimental and theoretical study of ceria in the WGS reaction, suggesting that the degree of surface reduction, specifically on the (1 0 0) facet exposed on ceria nanoparticles, has a major effect on the native activity of metal‐free ceria.…”

Section: Figurementioning

confidence: 97%

Water‐Gas‐Shift over Metal‐Free Nanocrystalline Ceria: An Experimental and Theoretical Study

et al. 2017

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Atandem experimental and theoretical investigation of amesoporousc eria catalyst reveals the properties of the metal oxide are conducive for activity typicallya scribed to metals, suggesting reducedC e 3 + and oxygen vacanciesa re responsible for the inherent bi-functionality of CO oxidation and dissociation of water required for facilitating the production of H 2 .T he degree of reduction of the ceria, specifically the (1 00)f ace, is found to significantly influence the binding of reagents,s uggesting reduced surfaces harbor the necessaryr eactive sites. The metal-free catalysis of the reaction is significantfor catalyst design considerations, and the suite of in situ analysesp rovides ac omprehensive study of the dynamic nature of the high surface areacatalystsystem.Thisstudy postulates feasible improvements in catalytic activity may redirect the purpose of the water-gas shiftreaction from CO purificationt oprimary hydrogen production. Figure 4. Calculated energy diagrams and structures for aWGS mechanism takingp lace in the presence of an adsorbed carbonate on the (1 00)s urface. The degree of reduction of the ceria surface influences the binding energies of the reactants,e specially for redox steps involving electron transfer between adsorbates andthe ceria surface. This indicatest hat morereducedceria surfaces bind Hr eagents more weakly,allowing for more facile formation of H 2 .Red, beige, grey,and white atomscorrespond to outermostO ,Ce, C, and H, respectively. Dark red and dark beige correspond to subsurface Oa nd subsurface Ce, respectively.The unit cell and the positiono fthe pre-adsorbed Ha tom are indicated in panel (a) by dashed lines and ab lue x,r espectively.

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“…Cámara et al studied the effect of a novel manganesedoped inverse CeO 2 /CuO catalyst under WGS reaction conditions [116]. The presence of Mn along with Cu strongly influenced the physical and chemical properties of the ceria nanoparticles leading to high catalytic activity towards WGS reaction [116]. They also examined CeO 2 /CuO, Mn-doped CuO, and Zn-doped CuO for WGS catalytic performance, and the effect of O 2 and/or H 2 present in the reaction mixture.…”

Section: Type Of Metal Oxide Supportmentioning

confidence: 99%

A review of recent advances in water-gas shift catalysis for hydrogen production

2020

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The water-gas shift reaction (WGSR) is an intermediate reaction in hydrocarbon reforming processes, considered one of the most important reactions for hydrogen production. Here, water and carbon monoxide molecules react to generate hydrogen and carbon dioxide. From the thermodynamics aspect, pressure does not have an impact, whereas low-temperature conditions are suitable for high hydrogen selectivity because of the exothermic nature of the WGSR reaction. The performance of this reaction can be greatly enhanced in the presence of suitable catalysts. The WGSR has been widely studied due do the industrial significance resulting in a good volume of open literature on reactor design and catalyst development. A number of review articles are also available on the fundamental aspects of the reaction, including thermodynamic analysis, reaction condition optimization, catalyst design, and deactivation studies. Over the past few decades, there has been an exceptional development of the catalyst characterization techniques such as near-ambient x-ray photoelectron spectroscopy (NA-XPS) and in situ transmission electron microscopy (in situ TEM), providing atomic level information in presence of gases at elevated temperatures. These tools have been crucial in providing nanoscale structural details and the dynamic changes during reaction conditions, which were not available before. The present review is an attempt to gather the recent progress, particularly in the past decade, on the catalysts for lowtemperature WGSR and their structural properties, leading to new insights that can be used in the future for effective catalyst design. For the ease of reading, the article is divided into subsections based on metals (noble and transition metal), oxide supports, and carbon-based supports. It also aims at providing a brief overview of the reaction conditions by including a table of catalysts with synthesis methods, reaction conditions, and key observations for a quick reference. Based on our study of literature on noble metal catalysts, atomic Pt substituted Mn 3 O 4 shows almost full CO conversion at 260°C itself with zero methane formation. In the case of transition metals group, the inclusion of Cu in catalytic system seems to influence the CO conversion significantly, and in some cases, with CO conversion improvement by 65% at 280°C. Moreover, mesoporous ceria as a catalyst support shows great potential with reports of full CO conversion at a low temperature of 175°C.

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Metal-Free Low-Temperature Water–Gas Shift Catalysis over Small, Hydroxylated Ceria Nanoparticles

Cited by 14 publications

References 53 publications

Adsorbate Pairing on Oxide Surfaces: Influence on Reactivity and Dependence on Oxide, Adsorbate Pair, and Density Functional

Adsorbate Pairing on Oxide Surfaces: Influence on Reactivity and Dependence on Oxide, Adsorbate Pair, and Density Functional

Water‐Gas‐Shift over Metal‐Free Nanocrystalline Ceria: An Experimental and Theoretical Study

A review of recent advances in water-gas shift catalysis for hydrogen production

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