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See detailStochastic models of disordered mesoporous materials for small-angle scattering analysis and more
Gommes, Cédric ULiege

in Microporous and Mesoporous Materials (2018), 257

Small-angle scattering of either x-rays (SAXS) or neutrons (SANS) is one of the few experimental techniques that can be used to study the structure of porous materials on the entire range from 1 to 100 nm ... [more ▼]

Small-angle scattering of either x-rays (SAXS) or neutrons (SANS) is one of the few experimental techniques that can be used to study the structure of porous materials on the entire range from 1 to 100 nm, which makes it particularly suited for mesoporous materials. Because the information in scattering patterns is a correlation function, models are generally needed to convert data into structurally meaningful information. In this paper, we discuss five stochastic models that capture qualitatively different disordered structures, notably concerning the connectivity and the tortuosity of the phases. The models are two variants of the Boolean model, a dead leaves model, as well as two clipped Gaussian field models. The paper is illustrated with the SAXS analysis of a polymer xerogel, of a fumed silica as well as of a mesoporous alumina, and the fitted models are compared with pore size distributions derived from nitrogen adsorption. In the case of the xerogel and silica it is possible to pinpoint a single model that describes the structure best. In the case of the alumina, however, the scattering cannot discriminate the models. Even so, the models are useful because they enable one to quantitate the structural ambiguity of the SAXS data. [less ▲]

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See detailSmall-Angle Scattering in Porous Materials: an overview highlighting data-analysis challenges
Gommes, Cédric ULiege

Speech/Talk (2017)

Countless technologies and chemical processes make use of nanoporous materials: heterogeneous catalysis, including electrochemical reactions in fuel-cell electrodes, adsorption separation processes ... [more ▼]

Countless technologies and chemical processes make use of nanoporous materials: heterogeneous catalysis, including electrochemical reactions in fuel-cell electrodes, adsorption separation processes, kinetically selective membrane processes, are but a few examples. Small-angle scattering of either x-rays (SAXS) or neutrons (SANS) is one of the few experimental methods available for the in situ analysis of phenomena in this type of materials at the mesoscopic scale. In this presentation, we briefly review some recent applications of small-angle scattering to empty and loaded mesoporous solids [1-3]. A particular focus is put on the data analysis challenges, whereby the scattered intensity is converted to real-space structures with nanometer resolution [4,5]. [less ▲]

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See detailDerjaguin-Broekhoff-de Boer analysis of adsorption in very disordered mesopores using probabilistic models
Gommes, Cédric ULiege

Conference (2017, May 08)

Our current ability to produce mesoporous materials with ordered morphology has raised fascinating questions about the impact of geometrical disorder on adsorption and desorption states [1]. Many recent ... [more ▼]

Our current ability to produce mesoporous materials with ordered morphology has raised fascinating questions about the impact of geometrical disorder on adsorption and desorption states [1]. Many recent works have investigated the role of mild elements of disorder, such as local constriction or corrugation superimposed to otherwise geometrically ideal cylindrical pores [2,3]. These works have notably shown that elements of disorder may act as nucleation sites and destabilize vapor-like metastable states. The relevance of these perturbation-like results to fundamentally disordered materials, such as gels, is unclear. In particular, do vapor-like metastable states exist at all in this type of very disordered material? In the present communication, we address this question using probabilistic models to investigate the role of disorder. We generalize the classical Gaussian field models of porous materials [4] and use them to analyze adsorption and desorption in the Derjaguin-Broekhof-de Boer approximation. Our approach differs from earlier contributions in that both the adsorbent and the adsorbate are described in terms of probabilities [5]. This enables us to analyze the adsorbate configuration in very disordered solids using a low-dimensional yet realistic configuration space. We notably show that vapor-like metastable states are unlikely in gel-like disordered materials. [less ▲]

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See detailSub-Micrometer Structure Formation during Spin Coating Revealed by Time-Resolved In Situ Laser and X-Ray Scattering
van Franeker, Jakobus; Hermida-Merino, Daniel; Gommes, Cédric ULiege et al

in Advanced Functional Materials (2017), 27

Solution-processed thin polymer films have many applications, such as organic electronics and block-copolymer nanofabrication. These films are often made by spin coating a solution that contains one or ... [more ▼]

Solution-processed thin polymer films have many applications, such as organic electronics and block-copolymer nanofabrication. These films are often made by spin coating a solution that contains one or more solids and can show different phase-separated structures. The formation mechanism of the droplet-like morphology is studied here by processing polystyrene (PS) and a fullerene derivative ([6,6]-phenyl-C71-butyric acid methyl ester, [70]PCBM) from o-xylene. The final structure consists of [70]PCBM droplets partially embedded in a PS-rich matrix showing interdomain distance of 100–1000 nm as determined from transmission electron microscopy and grazing incidence small angle X-ray scattering (GISAXS). To elucidate the formation of these morphologies in real time, ultrafast in situ GISAXS coupled with laser interferometry and laser scattering is performed during spin coating. In situ thickness measurements and laser scattering show that liquid–liquid phase separation occurs at ≈70 vol% solvent. Subsequently, in only 100–400 ms, almost dry [70]PCBM domains start to protrude from the swollen PS-rich matrix. These results are used to verify the ternary phase diagram calculated using Flory–Huggins theory. The discussed multitechnique approach can be applied to study fundamental aspects in soft matter such as phase separation in thin films occurring at very short time scales. [less ▲]

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See detailScale-dependent diffusion anisotropy in nanoporous silicon
Kondrashova, D; Lauerer, A; Mehlhorn, D et al

in Scientific Reports (2017), 7

Nanoporous silicon produced by electrochemical etching of highly B-doped p-type silicon wafers can be prepared with tubular pores imbedded in a silicon matrix. Such materials have found many technological ... [more ▼]

Nanoporous silicon produced by electrochemical etching of highly B-doped p-type silicon wafers can be prepared with tubular pores imbedded in a silicon matrix. Such materials have found many technological applications and provide a useful model system for studying phase transitions under con nement. This paper reports a joint experimental and simulation study of di usion in such materials, covering displacements from molecular dimensions up to tens of micrometers with carefully selected probe molecules. In addition to mass transfer through the channels, di usion (at much smaller rates) is also found to occur in directions perpendicular to the channels, thus providing clear evidence of connectivity. With increasing displacements, propagation in both axial and transversal directions is progressively retarded, suggesting a scale-dependent, hierarchical distribution of transport resistances (“constrictions” in the channels) and of shortcuts (connecting “bridges”) between adjacent channels. The experimental evidence from these studies is con rmed by molecular dynamics (MD) simulation in the range of atomistic displacements and rationalized with a simple model of statistically distributed “constrictions” and “bridges” for displacements in the micrometer range via dynamic Monte Carlo (DMC) simulation. Both ranges are demonstrated to be mutually transferrable by DMC simulations based on the pore space topology determined by electron tomography. [less ▲]

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See detailSmall-angle scattering analysis of empty or loaded hierarchical porous materials
Gommes, Cédric ULiege

Conference (2016, October)

Small-angle scattering (SAXS or SANS) is one of the few experimental methods available for the nanometer-scale study of physicochemical phenomena inside porous solids. Its potential, however, is often ... [more ▼]

Small-angle scattering (SAXS or SANS) is one of the few experimental methods available for the nanometer-scale study of physicochemical phenomena inside porous solids. Its potential, however, is often limited by the lack data analysis methods to convert scattering data into real-space structural information. This is notably the case for most porous materials of practical interest, which exhibit a hierarchical structure with micro, meso, and macropores, with often a secondary material confined in the pores, such as in supported catalysts, as well as fuel-cell and battery materials. Here, we discuss a general SAXS data analysis methodology for this type of material. Assuming that each structural level is statistically independent from the others and has a distinct characteristic length scale, compact mathematical expressions are derived for the scattering of the entire hierarchical structure [J.Phys.Chem.C, in press]. The method is illustrated with the SAXS analysis of SBA-15 micro- and meso-porous silica loaded with copper nitrate, as well as to supported catalysts obtained after calcining that material. The SAXS analysis shows that the nitrate permeates both the micro and mesopores, while the metallic copper obtained after calcination is found only in the mesopores. Moreover, the spatial distribution of the metal depends on the specifics of the calcination, as confirmed by electron tomography [Angew.Chem. 54 (2015) 11804]. The general methodology will be of interest to anyone interested in the quantitative analysis of small-angle scattering data from empty or loaded porous solids, and from any type of hierarchical material. [less ▲]

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See detailIntegrated Project with Focus on Energy Transition and Circular Economy for Developing Engineering Students' Soft Skills
Léonard, Grégoire ULiege; Pfennig, Andreas ULiege; Toye, Dominique ULiege et al

Poster (2016, September 05)

The present work reports the experience of an integrated project developed at the University of Liege for master students in chemical engineering. The goals are to promote the acquisition of soft skills ... [more ▼]

The present work reports the experience of an integrated project developed at the University of Liege for master students in chemical engineering. The goals are to promote the acquisition of soft skills and to consolidate technical knowledge by integrating and linking chemical engineering disciplines usually taught separately. A case study was selected to address some of the challenges related to energy transition: students had to design the energy system of a remote island and make it as energy independent and CO2-neutral as possible by 2030. The course of action during the academic year, the assessment of soft skills, and the tools offered to ease the mentoring and encourage the acquisition of soft skills are described. Not all implemented techniques performed equally well, and this project finally appeared to be a challenge for the teaching team as well. [less ▲]

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See detailProbabilistic models of porous materials
Gommes, Cédric ULiege

Scientific conference (2016, June)

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See detailSmall-angle scattering and scale-dependent heterogeneity
Gommes, Cédric ULiege

in Journal of Applied Crystallography (2016), 49

Although small-angle scattering is often discussed qualitatively in terms of material heterogeneity, when it comes to quantitative data analysis this notion becomes somehow hidden behind the concept of ... [more ▼]

Although small-angle scattering is often discussed qualitatively in terms of material heterogeneity, when it comes to quantitative data analysis this notion becomes somehow hidden behind the concept of correlation function. In the present contribution, a quantitative measure of heterogeneity is defined, it is shown how it can be calculated from scattering data, and its structural significance for the purpose of material characterization is discussed. Conceptually, the procedure consists of using a finite probe volume to define a local average density at any point of the material; the heterogeneity is then quantitatively defined as the fluctuations of the local average density when the probe volume is moved systematically through the sample. Experimentally, it is shown that the so-defined heterogeneity can be estimated by projecting the small-angle scattering intensity onto the form factor of the chosen probe volume. Choosing probe volumes of various sizes and shapes enables one to comprehensively characterize the heterogeneity of a material over all its relevant length scales. General results are derived for asymptotically small and large probes in relation to the material surface area and integral range. It is also shown that the correlation function is equivalent to a heterogeneity calculated with a probe volume consisting of two points only. The interest of scale-dependent heterogeneity for practical data analysis is illustrated with experimental small-angle X-ray scattering patterns measured on a micro- and mesoporous material, on a gel, and on a semi-crystalline polyethylene sample. Using different types of probes to analyse a given scattering pattern enables one to focus on different structural characteristics of the material, which is particularly useful in the case of hierarchical structures. [less ▲]

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See detailRevealing the formation of copper nanoparticles from a homogeneous solid precursor by electron microscopy
Van den Berg, Roy; Elkjaer, Christian; Gommes, Cédric ULiege et al

in Journal of the American Chemical Society (2016)

The understanding of processes leading to the formation of nanometer-sized particles is important for tailoring of their size, shape and location. The growth mechanisms and kinetics of nanoparticles from ... [more ▼]

The understanding of processes leading to the formation of nanometer-sized particles is important for tailoring of their size, shape and location. The growth mechanisms and kinetics of nanoparticles from solid precursors are, however, often poorly described. Here we employ transmission electron microscopy (TEM) to examine the formation of copper nanoparticles on a silica support during the reduction by H2 of homogeneous copper phyllosilicate plates, as a prototype precursor for a co-precipitated catalyst. Specifically, time-lapsed TEM image series acquired of the material during the reduction provide a direct visualization of the growth dynamics of an ensemble of individual nanoparticles and enable a quantitative evaluation of the nucleation and growth of the nanoparticles. This quantitative information is compared with kinetic models and found to be best described by a nucleation-and-growth scenario involving autocatalytic reduction of the copper phyllosilicate followed by diffusion-limited or reaction-limited growth of the copper nanoparticles. The plate-like structure of the precursor restricted the diffusion of copper and the autocatalytic reduction limited the probability for secondary nucleation. The combination of a uniform size of precursor particles and the autocatalytic reduction thus offers means to synthesize nanoparticles with well-defined sizes in large amounts. In this way, in situ observations made by electron microscopy provide mechanistic and kinetic insights into the formation of metallic nanoparticles, essential for the rational design of nanomaterials. [less ▲]

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See detailSmall-Angle Scattering Analysis of Empty or Loaded Hierarchical Porous Materials
Gommes, Cédric ULiege; Prieto, Gonzalo; de Jongh, Petra

in Journal of Physical Chemistry C (2016), 120(3), 14881506

Small-angle scattering of x-rays (SAXS) or neutrons (SANS) is one of the few experimental methods that can in principle be used for the in situ study at the mesoscopic scale of physicochemical phenomena ... [more ▼]

Small-angle scattering of x-rays (SAXS) or neutrons (SANS) is one of the few experimental methods that can in principle be used for the in situ study at the mesoscopic scale of physicochemical phenomena occurring inside nanoporous solids. However, the potential of the method is often limited by the lack of suitable data analysis methods to convert scattering data into real-space structural information. This is notably the case for most porous materials of practical interest, which exhibit a hierarchical structure with micro, meso, and macropores, with often a secondary material confined in the pores, such as in supported catalysts, as well as fuel-cell and battery materials. In the present contribution, we propose a general analysis of x-ray scattering by this type of material. Assuming that each structural level is statistically independent from the others and has a distinct characteristic length scale, compact mathematical expressions are derived for the scattering of the entire hierarchical structure. The results are particularised to the SAXS analysis of SBA-15 ordered mesoporous silica loaded with copper nitrate as well as to supported catalysts obtained after heat treatment of that material. The SAXS data analysis shows that the nitrate fills both the micro and mesopores of the material, while the metallic copper obtained after heat treatment is found only in the mesopores. Moreover, the mesoscopic-scale spatial distribution of the metal depends on the heat treatment, in line with earlier electron tomography studies. The main ideas underlying the SAXS data analysis were presented in an recent Communication [Gommes et al., Angew. Chem. Intl. Ed. 54 (2015) 11804-11808]. Here we generalise the approach and we provide a comprehensive discussion of how any level in a hierarchical structure contributes to its overall scattering pattern. The results, as well as the general modelling methodology, will be of interest to anyone interested in the quantitative analysis of small-angle scattering data of empty or loaded porous solids, and more generally of any type of hierarchical material. [less ▲]

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See detailExplicit analysis of small-­‐angle scattering patterns in terms of scale-­dependent heterogeneity
Gommes, Cédric ULiege

Scientific conference (2015, November 13)

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See detailThe Number of Structures Compatible with any Specified Correlation Function
Gommes, Cédric ULiege

Conference (2015, September)

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See detailSmall-Angle Scattering in Porous Solids, an overview highlighting data analysis challenges
Gommes, Cédric ULiege

Conference (2015, June)

Countless technologies and chemical processes make use of nanoporous materials: heterogeneous catalysis, including electrochemical reactions in fuel-cell electrodes, adsorption separation processes ... [more ▼]

Countless technologies and chemical processes make use of nanoporous materials: heterogeneous catalysis, including electrochemical reactions in fuel-cell electrodes, adsorption separation processes, kinetically selective membrane processes, are but a few examples. Nanopores are also relevant to natural processes as diverse as the weathering of rocks and ion transport through biological membranes.[1] Small-angle scattering of x-rays (SAXS) or neutrons (SANS) is one of the few experimental methods currently available for the in situ analysis of phenomena in this type of materials at the mesoscopic scale.[e.g. 2,3] In this presentation, we briefly review some recent applications of small-angle scattering to the in situ analysis of phenomena inside mesoporous solids. A particular focus is put on the data analysis challenges, whereby the scattered intensity is converted to real-space structures with nanometer resolution. [less ▲]

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See detailNanometer-scale wetting transitions in mesopores: a SAXS analysis
Gommes, Cédric ULiege

Conference (2015, May)

The equilibrium and metastable configurations of confined binary liquids has been a topic of research since the early work of Liu et al. in the nineties [1]. In particular, it has been proposed ... [more ▼]

The equilibrium and metastable configurations of confined binary liquids has been a topic of research since the early work of Liu et al. in the nineties [1]. In particular, it has been proposed theoretically that liquids may coexist inside nanopores in the form of layers covering uniformly the solid surface, of plugs filling locally the pore space, or of capsules floating in the middle of the pores. In the present contribution, we report in situ synchrotron small-angle scattering (SAXS) experiments on hexane/nitrobenzene solutions confined in mesoporous carbon xerogels [2]. The SAXS shows that these systems exhibit reversible temperature-induced transitions between the layer and the plug configurations. The scattering data is analyzed using a so-called plurigaussian model, which enables us to reconstruct the configurations of the confined liquids, and quantitatively analyze the wetting transitions at the nanometer-scale in terms of changing interface areas, contact angles, and triple-line lengths. [less ▲]

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See detailDerjaguin-Broekhoff-de Boer analysis of adsorption in very disordered mesopores using probabilistic models
Gommes, Cédric ULiege

Poster (2015, May)

Our current ability to produce mesoporous materials with ordered morphology has raised fascinating questions about the impact of geometrical disorder on adsorption and desorption states [1]. Many recent ... [more ▼]

Our current ability to produce mesoporous materials with ordered morphology has raised fascinating questions about the impact of geometrical disorder on adsorption and desorption states [1]. Many recent works have investigated the role of mild elements of disorder, such as local constriction or corrugation superimposed to otherwise geometrically ideal cylindrical pores [2,3]. These works have notably shown that elements of disorder may act as nucleation sites and destabilize vapor-like metastable states. The relevance of these perturbation-like results to fundamentally disordered materials, such as gels, is unclear. In particular, do vapor-like metastable states exist at all in this type of very disordered material? In the present communication, we address this question using probabilistic models to investigate the role of disorder. We generalize the classical Gaussian field models of porous materials [4] and use them to analyze adsorption and desorption in the Derjaguin-Broekhof-de Boer approximation. Our approach differs from earlier contributions in that both the adsorbent and the adsorbate are described in terms of probabilities [5]. This enables us to analyze the adsorbate configuration in very disordered solids using a low-dimensional yet realistic configuration space. We notably show that vapor-like metastable states are unlikely in gel-like disordered materials. [1] D.Wallacher, N. Künzner, D. Kovalev, N. Knorr, K. Knorr, Capillary condensation in linear mesopores of different shape, Phys. Rev. Lett. 92 (2004) 195704; [2] B. Coasne, A. Galarneau, F. Di Renzo, R.M.J. Pellenq, Effect of morphological defects on gas adsorption in nanoporous silicas, J. Phys. Chem. C 111 (2007) 15759; [3] C.J. Gommes, Adsorption, capillary bridge formation, and cavitation in SBA-15 corrugated mesopores: A Derjaguin-Broekhoff-de Boer analysis, Langmuir 28 (2012) 5101-5115; [4] R.J. Pellenq, P. levitz, Capillary condensation in a disordered mesoporous medium: A grand canonical Monte Carlo study, Molecular Physics 100 (2002) 2059;[5] C.J. Gommes, A.P. Roberts, in preparation. [less ▲]

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See detailMesoscale Characterization of Nanoparticles Distribution Using X-Ray Scattering
Gommes, Cédric ULiege; Prieto, Gonzalo; Zecevic, Jovana et al

in Angewandte Chemie International Edition (2015), 54

The properties of many functional materials depend critically on the spatial distribution of an active phase within a matrix or support material. In the case of solid catalysts, controlling the spatial ... [more ▼]

The properties of many functional materials depend critically on the spatial distribution of an active phase within a matrix or support material. In the case of solid catalysts, controlling the spatial distribution of metal (oxide) nanoparticles at the mesoscopic scale offers new strategies to tune their performance and enhance their lifetimes. However, such advanced control requires the development of suitable methods to characterize the spatial distribution of nanoparticles at the mesoscopic scale. Currently electron microscopy and more specifically electron tomography is close to being the only option. Here, we show how the background in x-ray scattering patterns can be analyzed to quantitatively access the distribution of metal nanoparticles within support materials displaying hierarchical porosity. Our approach is illustrated for copper catalysts supported on meso- and micro-porous silica, which display distinctly different metal spatial distributions. Results derived from the modeling of x-ray scattering patterns are in excellent agreement with electron tomography observations, while the amount of material being characterized at once is enhanced by twelve orders of magnitude. Our strategy opens unprecedented prospects to understand structure-property relationships and to guide the synthesis of advanced supported catalysts as well as a wide array of other functional nanomaterials. [less ▲]

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See detailSmall Angle X-ray Scattering Insights into the Architecture-Dependent Emulsifying Properties of Amphiphilic Copolymers in Supercritical Carbon Dioxide
Alaimo, David ULiege; Hermida Merino, Daniel; Grignard, Bruno ULiege et al

in Journal of Physical Chemistry B (2015), 119

The supramolecular assembly of a series of copolymers combining a PEO-rich hydrophilic and fluorinated CO2-philic sequences is analysed by synchrotron small-angle xray scattering (SAXS) in supercritical ... [more ▼]

The supramolecular assembly of a series of copolymers combining a PEO-rich hydrophilic and fluorinated CO2-philic sequences is analysed by synchrotron small-angle xray scattering (SAXS) in supercritical CO2, as well as in water/CO2 emulsions. These copolymers were designed to have the same molecular weight and composition, and to differ only by their macromolecular architecture. The investigated copolymers have random, block, and palm-tree architectures. Besides, thermo-responsive copolymer is also analysed, having a hydrophilic sequence becoming water-insoluble around 41 °C, i.e. just above the critical point of CO2. At the length scale investigated by SAXS, only the random copolymer appears to self-assemble in pure CO2, in the form of a disordered microgel-like network. The random, block and thermo-responsive copolymers are all able to stabilize water/CO2 emulsions but not the copolymer with the palm-tree architecture, pointing at the importance of macromolecular architecture for the emulsifying properties. A modelling of the SAXS data shows that the block and the thermo-responsive copolymers form spherical micelle-like structures containing about 70 % water and 30 % polymer. [less ▲]

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See detailAn Eco-friendly Soft Template Synthesis of Mesostructured Silica-Carbon Nanocomposites for Acid Catalysis
Zhong, Ruyi; Peng, Li; de Clippel, P et al

in ChemCatChem (2015), 7

The synthesis of ordered mesoporous silica-carbon composites was explored by employing TEOS and sucrose as the silica and carbon precursor respectively, and the triblock copolymer F127 as a structure ... [more ▼]

The synthesis of ordered mesoporous silica-carbon composites was explored by employing TEOS and sucrose as the silica and carbon precursor respectively, and the triblock copolymer F127 as a structure-directing agent via an evaporation-induced self assembly (EISA) process. It is demonstrated that the synthesis procedures allow for control of the textural properties and final composition of these silica-carbon nano composites via adjustment of the effective SiO2/C weight ratio. Characterization by SAXS, N2 physisorption, HRTEM, TGA, and 13C and 29Si solid-state MAS NMR show a 2D hexagonal mesostructure with uniform large pore size ranging from 5.2 to 7.6 nm, comprising of separate carbon phases in a continuous silica phase. Ordered mesoporous silica and non-ordered porous carbon can be obtained by combustion of the pyrolyzed nano composites in air or etching with HF solution, respectively. Sulfonic acid groups can be readily introduced to such kind of silica-carbon nanocomposites by a standard sulfonation procedure with concentrated sulfuric acid. Excellent acid-catalytic activities and selectivities for the dimerization of styrene to produce 1,3-diphenyl-1-butene and dimerization of a-methylstyrene to unsaturated dimers were demonstrated with the sulfonated materials. [less ▲]

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See detailSupport Functionalization To Retard Ostwald Ripening in Copper Methanol Synthesis Catalysts
Van den Berg, Roy; Parmentier, Tanja; Elkjaer, Christian et al

in ACS Catalysis (2015), 5

A main reason for catalyst deactivation in supported catalysts for methanol synthesis is copper particle growth. We have functionalized the support surface in order to suppress the formation and/or ... [more ▼]

A main reason for catalyst deactivation in supported catalysts for methanol synthesis is copper particle growth. We have functionalized the support surface in order to suppress the formation and/or transport of mobile copper species and thereby catalyst deactivation. A Stöber silica support was functionalized by treatment with aminopropyltriethoxysilane, which introduces aminopropyl groups on the surface. Copper was deposited on both unfunctionalized and functionalized Stöber silica via incipient wetness impregnation with aqueous copper nitrate solutions followed by drying and calcination. Similar particle size distributions (1−5 nm) were obtained for both supports by changing the flow of N2 to a flow of 2% NO/N2 during calcination of the unfunctionalized and amine functionalized silica, respectively. The effect of support functionalization with aminopropyl groups was an increased stability in the methanol synthesis reaction (40 bar, 260 °C, 23% CO/7% CO2/60% H2/10% Ar, 3% COx conversion) due to more limited copper particle growth as determined by transmission electron microscopy (TEM). Changing the interparticle distance did not have an influence on the deactivation rate, while the addition of few very large copper particles did, indicating that Ostwald ripening was most probably the dominant particle growth mechanism for these samples. In situ TEM images showed the contact angle between the reduced copper particles and the support. As shape and size was similar on silica as on amine-functionalized silica, the thermodynamic stability of the copper particles was unaltered. The driving force for copper particle growth was thus unchanged upon functionalization. We therefore suggest that Ostwald ripening in methanol synthesis catalysts was retarded by inhibiting the transport of copper species over the support surface. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed a decrease in the number of surface groups (hydroxyl, methoxy, and aminopropyl) upon functionalization because aminopropyltriethoxysilane reacted with multiple hydroxyl groups. Because of that, the distance between neighboring functional groups was increased, suppressing the mobility of Ostwald ripening species from one copper particle to another. [less ▲]

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