Publications (19) View all
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Article: Heterogeneities of the Nanostructure of Pt/Zeolite Y Catalysts Revealed by Electron Tomography.
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ABSTRACT: To develop structure-performance relationships for important catalysts, a detailed characterization of their morphology is essential. Using electron tomography we determined in three-dimensions the structure of Pt/zeolite Y bifunctional catalysts. Optimum experimental conditions enabled high resolution 3D imaging and the first confirmation of Pt particles as small as 1 nm located inside zeolite micropores, as was postulated decades ago. Semi-automated image analysis of 3D reconstructions provided an efficient study of numbers, size distributions and inter-particle distances of thousands of Pt particles within individual zeolite crystals. Upon extending this approach to a number of zeolite crystals of one batch of Pt/zeolite Y catalyst heterogeneities were revealed. The Pt loading, an important parameter for catalyst performance, varied between zeolite crystals up to a factor of 35. This discovery calls for re-evaluation of catalyst preparation methods and suggests potential for lowering the nominal loading with noble metals.ACS Nano 03/2013; · 10.77 Impact Factor -
Article: Ion-association complexes unite classical and non-classical theories for the biomimetic nucleation of calcium phosphate.
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ABSTRACT: Despite its importance in many industrial, geological and biological processes, the mechanism of crystallization from supersaturated solutions remains a matter of debate. Recent discoveries show that in many solution systems nanometre-sized structural units are already present before nucleation. Still little is known about the structure and role of these so-called pre-nucleation clusters. Here we present a combination of in situ investigations, which show that for the crystallization of calcium phosphate these nanometre-sized units are in fact calcium triphosphate complexes. Under conditions in which apatite forms from an amorphous calcium phosphate precursor, these complexes aggregate and take up an extra calcium ion to form amorphous calcium phosphate, which is a fractal of Ca(2)(HPO(4))(3)(2-) clusters. The calcium triphosphate complex also forms the basis of the crystal structure of octacalcium phosphate and apatite. Finally, we demonstrate how the existence of these complexes lowers the energy barrier to nucleation and unites classical and non-classical nucleation theories.Nature Communications 01/2013; 4:1507. · 7.40 Impact Factor -
Article: Towards stable catalysts by controlling collective properties of supported metal nanoparticles.
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ABSTRACT: Supported metal nanoparticles play a pivotal role in areas such as nanoelectronics, energy storage/conversion and as catalysts for the sustainable production of fuels and chemicals. However, the tendency of nanoparticles to grow into larger crystallites is an impediment for stable performance. Exemplarily, loss of active surface area by metal particle growth is a major cause of deactivation for supported catalysts. In specific cases particle growth might be mitigated by tuning the properties of individual nanoparticles, such as size, composition and interaction with the support. Here we present an alternative strategy based on control over collective properties, revealing the pronounced impact of the three-dimensional nanospatial distribution of metal particles on catalyst stability. We employ silica-supported copper nanoparticles as catalysts for methanol synthesis as a showcase. Achieving near-maximum interparticle spacings, as accessed quantitatively by electron tomography, slows down deactivation up to an order of magnitude compared with a catalyst with a non-uniform nanoparticle distribution, or a reference Cu/ZnO/Al(2)O(3) catalyst. Our approach paves the way towards the rational design of practically relevant catalysts and other nanomaterials with enhanced stability and functionality, for applications such as sensors, gas storage, batteries and solar fuel production.Nature Material 11/2012; · 32.84 Impact Factor -
Article: Mesoporosity of zeolite Y: quantitative three-dimensional study by image analysis of electron tomograms.
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ABSTRACT: Quantitative insight into the three-dimensional morphology of complex zeolite Y mesopore networks was achieved by combining electron tomography and image processing. Properties could be studied that are not measurable by other techniques, such as the size distribution of the intact microporous domains. This has great relevance in descriptions of the molecular diffusion through zeolite crystals and, hence, catalytic activity and selectivity.Angewandte Chemie International Edition 03/2012; 51(17):4213-7. · 13.45 Impact Factor -
Article: A quantitative electron tomography study of ruthenium particles on the interior and exterior surfaces of carbon nanotubes.
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ABSTRACT: The efficiency of filling carbon nanotubes (CNTs) by ultrasound-assisted wet impregnation is quantified by electron tomography (ET). For image analysis, a method that combines edge detection with single-value thresholding is proposed and validated. A high proportion (80 wt %) of the ruthenium was deposited inside the tube at an average particle size of 2-4 nm. Particles located on the outer surface of the CNT had a size of 1-3 nm. The local ruthenium loading measured by ET (3.2 wt %) closely matched the value from elemental analysis (3.5 wt %). In addition, a few 1 nm-sized ruthenium particles were detected inside the carbon wall, which contained pores/cracks. Direct imaging and quantification is a powerful tool to understand and possibly model the unique properties of CNT-based catalysts.ChemSusChem 01/2011; 4(7):957-63. · 6.83 Impact Factor
