The size-dependent site composition of FCC cobalt nanocrystals

Helden, Pieter van; Ciobîcă, Ionel M.; Coetzer, R.L.J.

doi:10.1016/j.cattod.2015.07.052

Cited by 127 publications

(179 citation statements)

References 44 publications

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“…Samples A, B and F were chosen because they showed sufficient X-ray absorption (that is, Ni weight loading), and because the particles on the catalysts were predominantly below 3 nm, which theoretically ensures > 35% surface atoms and thus sufficient signal in bulk Q-XAS to detect surface changes 42,43 . The larger particle sizes were chosen to verify observed trends.…”

Section: Nature Catalysismentioning

confidence: 99%

Unravelling structure sensitivity in CO2 hydrogenation over nickel

et al. 2018

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T he reduction of CO 2 emissions into the Earth's atmosphere is gaining legislative importance in view of its impact on the climate [1][2][3][4][5] . Reduction of the harmful effect of these emissions through reclamation of CO 2 is made attractive because CO 2 can be a zero-or even negative-cost carbon feedstock 6,7 . The conversion of renewably produced hydrogen and CO 2 into methane, or synthetic natural gas, over Ni is a solution that combines the potential to reduce CO 2 emissions with a direct answer to the temporal mismatch in renewable electricity production capacity and demand [8][9][10][11][12][13][14][15][16][17] . Chemical energy storage in the form of hydrogen production by electrolysis is a relatively mature technology; however, the required costly infrastructure, and inefficiencies in distribution and storage deem it inconvenient for large-scale application in the near future. Point-source CO 2 hydrogenation to methane represents an alternative approach with higher energy density. Furthermore, methane is more easily liquefied and can be stored safely in large quantities through infrastructures that already exist 18,19 . Power-to-gas (in this case methane) is thus actively considered as being capable of balancing electric grid stability, which will allow us to increase the renewable energy supply 20 .The search for fossil fuel alternatives, and application of a process such as that described above can arguably be achieved only with the help of advances in catalysis and the closely related field of nanomaterials. Continuous efforts in both fields have allowed us to make increasingly smaller and catalytically more active (metal) particles. However, it is already known that making progressively smaller supported catalyst particles does not necessarily linearly correspond to higher catalytic activity [21][22][23] . This phenomenon, where not all atoms in a supported metal catalyst have the same activity, is called structure sensitivity and is often attributed to the distinctly different chemistries on different lattice planes for π -bond activation in CO 2 , or σ -bond activation in, for example H 2 dissociation and C-H propagation 21,24 . The availability of stepped (less coordinated) versus terrace (more coordinated) sites on the surface of supported catalyst nanoparticles obviously changes with particle size, and atomic geometries become particularly interesting below 2 nm where, for example, π -bond activation is believed to not be able to occur 21 . While particle-size effects have been extensively studied for CO hydrogenation over Co 23,25 , the understanding of such structure sensitivity effects for these critical smaller metal particle sizes is lacking as sub-2-nm particles prove difficult to synthesize for first-row transition metals (Co, Fe and Ni). However, a particle-size effect for CO 2 hydrogenation is much less well established 26 .Here, we used a unique set of SiO 2 -supported Ni nanoparticles with diameters ranging from 1 to 7 nm in size, and show not only the existence of a distinct pa...

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Section: Nature Catalysismentioning

confidence: 99%

Unravelling structure sensitivity in CO2 hydrogenation over nickel

et al. 2018

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“…Since the activity showed a particle size dependence, the partial pressure of ethylene oxide differs per sample. When corrected for these secondary reactions with a rate of EO oxidation obtained from experiments over bare supports, they obtained a slight decrease in selectivity with particle size [32]. They believed that the actual particle size dependency of the selectivity toward ethylene oxide lies somewhere between the observed and the corrected trend [35].…”

Section: à2mentioning

confidence: 98%

“…In these reactions, metal particles smaller than 6-8 nm exhibit significantly lower turnover frequencies (TOF) than larger particles, while larger metal particles exhibit particle size independent TOF's [29]. The CO activation requires an ensemble of surface atoms, which are unique to step-edge sites (B5-type sites), which in turn are rare on particles smaller than 10 nm [31,32]. In ethylene epoxidation the particle size effect follows a trend similar to the Fischer-Tropsch reaction, but it occurs at particle sizes an order of magnitude larger.…”

Section: à2mentioning

confidence: 99%

Preparation and particle size effects of Ag/α-Al2O3 catalysts for ethylene epoxidation

Reijen

Kanungo

Welling

et al. 2017

Journal of Catalysis

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a-AluminaCatalyst design Ethylene oxide Particle size effect a b s t r a c t Currently, for the industrial ethylene epoxidation a-alumina supported silver catalysts are the only catalyst of choice. We demonstrate a novel method to produce these catalysts with different silver particle sizes, but without changing other key parameters that may affect the catalytic performance such as support specific surface area or metal precursor. a-Alumina was impregnated with a silver oxalate solution, and was subsequently dried and treated in different gas atmospheres and at different temperatures to tune the silver particle sizes in the range of 20-500 nm. Particles of 20 nm exhibited a lower turnover frequency than particles of 70 nm and larger, which exhibit a constant turnover frequency, in accordance with results in literature. However, the selectivity, when measured at constant conversion, was particle size independent. This is the first time that the effect of the particle size on the selectivity of ethylene epoxidation is reported at constant conversion. This was made possible by a new method of producing supported silver catalysts, which we expect that is also applicable for silver catalysts with other supports and for the preparation of other supported metal catalysts.

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“…In a recent paper van Helden et al describe a theoretical approach to model the structures of realistic fcc Co crystallites [40]. An example of a thus obtained 4.6 nm Co particle is shown in Fig.…”

Section: Co Activation and Oxygen Hydrogenationmentioning

confidence: 98%

“…In this dual site mechanism, CO is thought to dissociate on step sites, whereas chain growth occurs on the close-packed terraces (e.g. (111) facets of fcc particles), which make up about 65% of the particle surface [40]. After CO bond scission C is hydrogenated to CH x and diffuses from the step edges onto the adjacent close-packed terraces where chain growth occurs via coupling of CH with an alkylidyne (C-R) adsorbate.…”

Section: Chain Growth Mechanismsmentioning

confidence: 99%