| 1. |
- Aramburo, Luis R., et al.
(författare)
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The Porosity, Acidity, and Reactivity of Dealuminated Zeolite ZSM-5 at the Single Particle Level : The Influence of the Zeolite Architecture
- 2011
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 17:49, s. 13773-13781
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Tidskriftsartikel (refereegranskat)abstract
- A combination of atomic force microscopy (AFM), high-resolution scanning electron microscopy (HR-SEM), focused-ion-beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), confocal fluorescence microscopy (CFM), and UV/Vis and synchrotron-based IR microspectroscopy was used to investigate the dealumination processes of zeolite ZSM-5 at the individual crystal level. It was shown that steaming has a significant impact on the porosity, acidity, and reactivity of the zeolite materials. The catalytic performance, tested by the styrene oligomerization and methanol-to-olefin reactions, led to the conclusion that mild steaming conditions resulted in greatly enhanced acidity and reactivity of dealuminated zeolite ZSM-5. Interestingly, only residual surface mesoporosity was generated in the mildly steamed ZSM-5 zeolite, leading to rapid crystal coloration and coking upon catalytic testing and indicating an enhanced deactivation of the zeolites. In contrast, harsh steaming conditions generated 550 nm mesopores, extensively improving the accessibility of the zeolites. However, severe dealumination decreased the strength of the Bronsted acid sites, causing a depletion of the overall acidity, which resulted in a major drop in catalytic activity.
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| 2. |
- Brent, Rhea, et al.
(författare)
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Unstitching the Nanoscopic Mystery of Zeolite Crystal Formation
- 2010
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 132:39, s. 13858-13868
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Tidskriftsartikel (refereegranskat)abstract
- A molecular-scale understanding of crystal growth is critical to the development of important materials such as pharmaceuticals, semiconductors and catalysts. Only recently has this been possible with the advent of atomic force microscopy that permits observation of nanoscopic features on solid surfaces under a liquid or solution environment. This allows in Situ measurement of important chemical transformations such as crystal growth and dissolution. Further, the microscope can access not only an accurate height measurement of surface topography, important to deduce structural elements, but also the forces involved during nanoscopic processes. We have discovered that it is possible to use these features to "illuminate" critical nanoscopic chemical events at crystal surfaces and at the same time extract the associated energies and unstitch the details of the stepwise mechanism of growth and dissolution. This approach has been developed using nanoporous crystals of the heterogeneous catalyst zeolite L; however, in principle the approach could be adapted to many crystal growth problems.
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| 3. |
- Cubillas, Pablo, et al.
(författare)
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AFM and HRSEM Invesitigation of Zeolite A Crystal Growth. Part 1 : In the Absence of Organic Additives
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:25, s. 12567-12574
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Tidskriftsartikel (refereegranskat)abstract
- The crystallization of zeolite A by the verified synthesis method was studied by means of high-resolution scanning electron microscopy (HRSEM) and atomic force microscopy (AFM). These methods show an evolution in the growth mode of zeolite A from an adhesive type at the beginning of the synthesis (high supersaturation) to birth-and-spread growth at the end of the synthesis (low supersaturation). Additionally, HRSEM provides direct proof on the formation of zeolite A crystals at the surface of the amorphous gel and the aggregation of crystals at early stages of synthesis, which leads to intergrowth formation. For the first time, high-resolution AFM images were taken on the {110} and {111} faces of zeolite A. Growth on {110} faces takes place by a birth-and-spread mechanism, and the shape of the terraces is rectangular, with growth along the < 100 > directions being twice as fast as in the < 110 > directions. Growth on the {111} faces also takes place by a birth-and-spread mechanism via triangular-shaped terraces with edges parallel to < 110 > directions. Possible surface terminations for both faces are discussed, and crystal habit and surface topography are modeled by Monte Carlo simulations.
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| 4. |
- Cubillas, Pablo, et al.
(författare)
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Atomic Force Microscopy and High Resolution Scanning Electron Microscopy Investigation of Zeolite A Crystal Growth. Part 2 : In Presence of Organic Additives
- 2014
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:40, s. 23092-23099
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Tidskriftsartikel (refereegranskat)abstract
- The nanoscopic details of the crystal growth of zeolite. A in the presence of the organic modifiers. diethanolmaine (DEA) and triethanolamine (TEA) has been determined using a combination of atomic force microscopy (AFM) and high-resolution scanning electron microscopy (HRSEM) coupled with Monte Carlo simulations. Crystallization of zeolite A in the presence of TEA was faster than when the growing solution contained DEA. In addition, the morphology of the final zeolite A crystals depended on the type of organic molecule, with TEA producing crystals bound only by {100} facets and DEA leading to the formation of relatively large {110} faces. These features can be explained in terms of the relative Si/Al in the growing medium and its control due to the different affinity of the organic molecules to Al. In addition, synthesis Si/Al in the growing medium and its contorl due to the different affinity of the organic molecules to Al. In additon synthesis performed at 90 degrees C showed the apperance of {211} facets Careful review of the HRSEM and AFM images, in addition to comparion with the MC simulations, reveals that these are in fact pseudofacets products of the slow dissolution of the metastable zeolite. A crsytals. This proves that the final habit of the LTA crystals can be governed by very small changes in saturation of the growing medium, and control of this parameter can prove advantageous when designing crystals for industrial applications.
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| 5. |
- Cubillas, Pablo, et al.
(författare)
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Spiral Growth on Nanoporous Silicoaluminophosphate STA-7 as Observed by Atomic Force Microscopy
- 2009
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 9:9, s. 4041-4050
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Tidskriftsartikel (refereegranskat)abstract
- Atomic force microscopy was used to study the surface of STA-7 crystals. STA-7 is a silicoaluminophosphate, nanoporous solid formed by interlinked double six ring units (D6R). Observations showed the formation of three distinct types of spirals at tow supersaturation conditions. The {001} face shows spirals with isotropic shapes and a Burgers vector of 0.9 nm, which corresponds to one D6R or one unit cell along the < 001 > direction. The {100} face contains two distinct types of spirals. The first has a Burgers vector of 0.9 rim, or half a unit cell along < 100 >. This dislocation produces a change in the ""stacking"" sequence of the D6Rs generating all overgrowth with the AEI structure. The second type is an interlaced spiral and is generated by a dislocation with a Burgers vector of 1.8 nm or one unit cell, leading to the formation of two substeps each with a different growth anisotropy. This anisotropy is directed by the shape of the substep and the energetics of template attachment. The preponderance of a surface coating of a secondary phase will have significant consequences on applications reliant on intracrystalline diffusion, such as catalysis, where, owing to diffusion limitations, the outermost structure dominates the functional properties.
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| 6. |
- Jones, Benedict C, et al.
(författare)
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To which world regions does the valence-dominance model of social perception apply?
- 2021
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Ingår i: Nature Human Behaviour. - : Springer Science and Business Media LLC. - 2397-3374. ; 5:1, s. 159-169
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Tidskriftsartikel (refereegranskat)abstract
- Over the past 10 years, Oosterhof and Todorov's valence-dominance model has emerged as the most prominent account of how people evaluate faces on social dimensions. In this model, two dimensions (valence and dominance) underpin social judgements of faces. Because this model has primarily been developed and tested in Western regions, it is unclear whether these findings apply to other regions. We addressed this question by replicating Oosterhof and Todorov's methodology across 11 world regions, 41 countries and 11,570 participants. When we used Oosterhof and Todorov's original analysis strategy, the valence-dominance model generalized across regions. When we used an alternative methodology to allow for correlated dimensions, we observed much less generalization. Collectively, these results suggest that, while the valence-dominance model generalizes very well across regions when dimensions are forced to be orthogonal, regional differences are revealed when we use different extraction methods and correlate and rotate the dimension reduction solution. PROTOCOL REGISTRATION: The stage 1 protocol for this Registered Report was accepted in principle on 5 November 2018. The protocol, as accepted by the journal, can be found at https://doi.org/10.6084/m9.figshare.7611443.v1 .
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| 7. |
- Stevens, Sam M., et al.
(författare)
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Hierarchical porous materials : Internal structure revealed by argon ion-beam cross-section polishing, HRSEM and AFM
- 2011
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Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 13:4, s. 745-749
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution scanning electron microscopy coupled with argon ion-beam cross-section polishing and atomic force microscopy were used to reveal details about the interconnectivity of meso- and macroporous networks in silica hierarchical porous material. The material studied has ordered macro- and mesoporosity as well as a disordered microporosity that are created using organic templating agents. Latex spheres template the macro- porosity, mesophase self-assembly of block co-polymers template the mesoporosity and individual polymer chains template the microporosity. By polishing this composite material with an argon ion beam it is possible to reveal the internal structure with minimal structural damage. Direct imaging of the mesoporous network within such cross sections is possible using high-resolution scanning electron microscopy. These observations demonstrate a lack of interconnectivity between the mesoporous and macroporous networks.
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| 8. |
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| 9. |
- Stevens, Sam M, et al.
(författare)
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Nanoscale Electron Beam Damage Studied by Atomic Force Microscopy
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:43, s. 18441-18443
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Tidskriftsartikel (refereegranskat)abstract
- High-resoln. SEM (HRSEM) has recently been added to the arsenal of characterization tools for material scientists to observe nanoscale surface features on both conducting and insulating materials. It is now therefore crucial to understand whether the intense electron beam will damage the features of interest. The authors were able, for the 1st time, to measure and quantify this damage using a combination of HRSEM and at. force microscopy (AFM), and as a consequence, the bulk of the damage, expressed as a depression on the crystal surface, is confined primarily to a subsurface vol. Simulations demonstrate that the depth of the depression is proportional to the interaction vol. of impact electrons below the crystal surface. More importantly, the nanometer surface features are conserved, and there is negligible assocd. loss of the crit. information in nanoscopic surface topog. These results confirm the usefulness of HRSEM as a tool for surface anal. not only for scientists studying crystal growth but also for materials scientists analyzing any surface at the nanoscale.
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