Surface diffusion in porous catalysts

Weber, Daniel L.; Sederman, Andrew J.; Mantle, Michael D.; Mitchell, Jonathan; Gladden, Lynn F.

doi:10.1039/b921210h

Cited by 56 publications

(54 citation statements)

References 65 publications

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“…Over the past decades, it has emerged as an important concept in many areas of surface science, including catalysis, epitaxial growth, and electromigration of voids (3)(4)(5)(6)(7). Here, we demonstrated that surface diffusion also plays a pivotal role in determining the growth pathway of a seed and thus the shape or morphology taken by the final product in a solutionphase synthesis of metal nanocrystals.…”

mentioning

confidence: 82%

On the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals

Xia

Xie

Liu

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

370

457

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Controlling the shape or morphology of metal nanocrystals is central to the realization of their many applications in catalysis, plasmonics, and electronics. In one of the approaches, the metal nanocrystals are grown from seeds of certain crystallinity through the addition of atomic species. In this case, manipulating the rates at which the atomic species are added onto different crystallographic planes of a seed has been actively explored to control the growth pattern of a seed and thereby the shape or morphology taken by the final product. Upon deposition, however, the adsorbed atoms (adatoms) may not stay at the same sites where the depositions occur. Instead, they can migrate to other sites on the seed owing to the involvement of surface diffusion, and this could lead to unexpected deviations from a desired growth pathway. Herein, we demonstrated that the growth pathway of a seed is indeed determined by the ratio between the rates for atom deposition and surface diffusion. Our result suggests that surface diffusion needs to be taken into account when controlling the shape or morphology of metal nanocrystals. seeded growth | shape control | noble metals S urface diffusion is a general process that involves the motion of adsorbed atoms (adatoms), molecules, or atomic clusters on the surface of a solid material (1, 2). Over the past decades, it has emerged as an important concept in many areas of surface science, including catalysis, epitaxial growth, and electromigration of voids (3-7). Here, we demonstrated that surface diffusion also plays a pivotal role in determining the growth pathway of a seed and thus the shape or morphology taken by the final product in a solutionphase synthesis of metal nanocrystals. Fig. 1 schematically illustrates four possible pathways for the growth of a cubic seed. As a model system, we focused on Pd nanocubes with slight truncation at corners and edges, together with six side faces passivated by chemisorbed Br -ions. In the following discussion, we refer to them as "Pd cubic seeds" for simplicity. We chose them as seeds for two major reasons: (i) they had a well-defined shape, together with a set of low-index facets on the surface (8, 9); and (ii) their side faces are blocked by Br -ions to ensure selective deposition of atoms onto the corner sites during seed-mediated growth (10-12). These two distinctive features allowed us to easily track the deposition of atoms and their surface diffusion during a growth process by analyzing the shape or morphology of the final product.The newly formed Pd atoms resulting from the reduction of a Pd precursor are expected to deposit at the corners of a cubic seed because the side faces are blocked by the chemisorbed Br -ions (Fig. 1A, 1). Upon deposition, there will be two different options for these adatoms: staying at the corner sites or migrating to other sites, including edges and side faces, through surface diffusion (Fig. 1A, 2 and 3). It should be pointed out that only surface diffusion was allowed here to move atoms from corners to edg...

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mentioning

confidence: 82%

On the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals

Xia

Xie

Liu

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

370

457

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“…However, T 2 is further influenced by a translational correlation time associated with surface diffusion 27. 28 Consequently, when molecules adsorb on surfaces, changes in their translational and rotational dynamics influence T 2 more than T 1 , resulting in T 1 > T 2 29. In porous materials with a high surface‐to‐volume ratio, S / V , the observed relaxation rates are proportional to S / V ,30 so absolute T 1 and T 2 measurements cannot be readily used to compare interactions between materials with differing pore geometry, pore size and density of adsorption sites.…”

Section: Introductionmentioning

confidence: 99%

Interpretation of NMR Relaxation as a Tool for Characterising the Adsorption Strength of Liquids inside Porous Materials

D’Agostino

Mitchell

Mantle

et al. 2014

Chemistry A European J

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121

147

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Nuclear magnetic resonance (NMR) relaxation times are shown to provide a unique probe of adsorbate–adsorbent interactions in liquid-saturated porous materials. A short theoretical analysis is presented, which shows that the ratio of the longitudinal to transverse relaxation times (T1/T2) is related to an adsorbate–adsorbent interaction energy, and we introduce a quantitative metric esurf (based on the relaxation time ratio) characterising the strength of this surface interaction. We then consider the interaction of water with a range of oxide surfaces (TiO2 anatase, TiO2 rutile, γ-Al2O3, SiO2, θ-Al2O3 and ZrO2) and show that esurf correlates with the strongest adsorption sites present, as determined by temperature programmed desorption (TPD). Thus we demonstrate that NMR relaxation measurements have a direct physical interpretation in terms of the characterisation of activation energy of desorption from the surface. Further, for a series of chemically similar solid materials, in this case a range of oxide materials, for which at least two calibration values are obtainable by TPD, the esurf parameter yields a direct estimate of the maximum activation energy of desorption from the surface. The results suggest that T1/T2 measurements may become a useful addition to the methods available to characterise liquid-phase adsorption in porous materials. The particular motivation for this work is to characterise adsorbate–surface interactions in liquid-phase catalysis.

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“…This effect is denoted as pore diffusion [69]. On the pore surface, the molecular dynamics is altered by liquid-surface interaction (adsorption) as well as limited diffusion path, which can be described as surface diffusion [70].…”

Section: Pore and Surface Diffusionmentioning

confidence: 99%

Adsorption of pyridine from aqueous solutions by polymeric adsorbents MN 200 and MN 500. Part 2: Kinetics and diffusion analysis

Zhu

Moggridge

D’Agostino

2016

Chemical Engineering Journal

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Telephone: +44 (0)1223 334763Fax: +44 (0)1223 334796 2 AbstractThe adsorption kinetics of pyridine adsorption on Macronet adsorbents MN 200 and MN 500 from aqueous solution was investigated at various initial pyridine concentrations and temperatures. The Weber-Morris plots revealed the influence of both external film diffusion and intraparticle diffusion resistances. The two linear regions in Weber-Morris plots were attributed to macropore and micropore diffusion, which was associated to the bimodal pore size distribution of the adsorbents. New insights into the diffusion mechanisms were highlighted, with the proposed internal film diffusion resistance dominating into the macropore region, whereas homogeneous particle diffusion resistance describes diffusion in the micropore region. The importance of pore and surface diffusion in the micropores was noted in contributing to the observed diffusion kinetics. The pore diffusion coefficient was estimated from PFG (pulsedfield gradient) parameter and molecular diffusion coefficient of pyridine in bulk liquid. A greater contribution of the surface to the overall diffusion kinetics was found for MN 500 as inferred from a proposed calculation method, which agrees with its better adsorption performance. The overall findings highlight the effect of pore structure onto the diffusion mechanisms inside the pores and help to gain a better understanding into the adsorption kinetics of these Macronet adsorbents, which are promising materials for the removal of Nheterocyclic compounds from waste water.

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Surface diffusion in porous catalysts

Cited by 56 publications

References 65 publications

On the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals

On the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals

Interpretation of NMR Relaxation as a Tool for Characterising the Adsorption Strength of Liquids inside Porous Materials

Adsorption of pyridine from aqueous solutions by polymeric adsorbents MN 200 and MN 500. Part 2: Kinetics and diffusion analysis

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