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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 ULg

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 ULg; Pfennig, Andreas ULg; Toye, Dominique ULg 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. 1 Introduction and background Over the last few years, University authorities, industrial partners as well as national and international experts that evaluated the education quality of our Department (AEQES, CTI) strongly suggested that opportunities should be offered to students to increase their soft skills as part of their curriculum. Moreover, many developments in chemical engineering are related to energy transition and circular economy, which are both transdisciplinary to conventional lectures. In this paper, we present methods and mentoring tools developed to teach students technical and soft skills for multi-disciplinary topics. 2 Description of the integrated project Objectives and constraints were defined at the onset of the project for both technical and soft skills. The technical objective was to propose an energy system that would make Reunion Island as energy independent and CO2-neutral as possible by 2030. This idea originated in the challenge set by the Eurecha 2015 student contest[1], for which students had to design facilities for a sheikhdom: electricity, water recycling, production of fertilizers… In our case, Reunion Island (~850 000 inhabitants) was considered as a case study as it is remote, has large biomass resources and high potential for renewable energies. Besides the objectives mentioned above and in order to force students to look at chemical engineering processes, the treatment of wastewater was imposed as well as the use of a synthetic liquid fuel as energy carrier. The targeted soft skills included working in large groups of minimum 4 students, efficient communication of results in English - both written and oral -, ability to integrate knowledge from various disciplines, development of critical mind and demonstration of independent and creative thinking. 3 Course of actions A team of 8 professors and senior scientists mentored the project and contributed to its assessment. The 10-ECTS project was divided in two parts. In the fall semester, students made global energy balances to design the energy system that would fulfill the objectives. As a result, a Sankey diagram of the energy flows on Reunion Island by 2030 was produced to allow for an overview of the available Island’s resources and needs, as well as of processes that can make the link between resources and needs. In the spring semester, two processes identified in the first part, namely the synthesis of bio-ethanol and bio-methanol, were modelled in more details using commercial software. Different tools were used to encourage student initiatives and work: • The use of a shared on-line portfolio for students to gather their documents improved their internal communication, but this remained a marginal channel for communication with teachers • In the fall semester, students orally presented progress reports every two weeks. After a feedback to students, the teaching team met to discuss the achievements and set the objectives for the next two weeks. This was very positive for the communication inside the teaching team. However, presentations every fortnight implied a work overload for students that had to constantly focus on preparing the presentations. • From the beginning, students were strongly encouraged to reach out to field experts whose contacts were provided. However, they preferred to rely mostly on Internet as their main source of information and reached out only rarely for help and usually very late. • In the fall semester, students had to designate new team leaders in turn every fortnight. This was abandoned as it prevented the establishment of clear structures in the group, reducing its efficiency. • In the spring semester, work tables allowed students to work directly with the teacher specialized in their task. This was appreciated by students and teachers, and it needs to be further encouraged. • Help in the group organization and interactions was provided by the PSGO (psychology of groups and organizations). This also included videoscopy, i.e. filming the students during their presentations and analyzing the records with them. This help was appreciated by students. The assessment was based on technical results for 60%, and soft skills for 40%. The evaluation of technical skills was done partly by all teachers equally and partly by teachers whose expertise was the closest to the technical sub-tasks. For soft skills, efficient communication, creativity in the work and results and links with conventional lectures were assessed. Critical thinking was evaluated through the relevance of qualitative and quantitative results and discussions. Group work was assessed by the teachers as well as by students through mutual evaluation. 4 Conclusions and perspectives The integrated project gave students a first opportunity to improve their soft skills along with their technical knowledge. It also improved their communication skills and their fluency in English. The teaching team proposed different mentoring techniques to encourage efficient work, with varying results. Finally, as the assessment ignored soft skills improvements, it may be modified by evaluating soft skills all year long so both the final result and the observed improvements contribute to the grade. Reference Eurecha, The European Committee for the Use of Computers in Chemical Engineering Education, 2015. Announcement for student contest problem competition 2015. http://bari.upc.es/eurecha/. [less ▲]

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See detailProbabilistic models of porous materials
Gommes, Cédric ULg

Scientific conference (2016, June)

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

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 ULg 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 ULg; 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 ULg

Scientific conference (2015, November 13)

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

Conference (2015, September)

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

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 ULg

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 ULg

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 ULg; 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 ULg; Hermida Merino, Daniel; Grignard, Bruno ULg 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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See detailThe range of validity of sorption kinetic models
Douven, Sigrid ULg; Pàez Martinez, Carlos ULg; Gommes, Cédric ULg

in Journal of Colloid & Interface Science (2015), 448

Several hundred papers are published yearly reporting liquid-phase adsorption kinetics data. In general the data is analyzed using a variety of standard models such as the pseudo first- and second-order ... [more ▼]

Several hundred papers are published yearly reporting liquid-phase adsorption kinetics data. In general the data is analyzed using a variety of standard models such as the pseudo first- and second-order models and the Intraparticle-Diffusion model. The validity of these models is often assessed empirically via their ability to fit the data, independently of their physicochemical soundness. The aim of the present paper is to rationalize the analysis of liquid-phase adsorption kinetics data, and to investigate experimental factors that influence the adsorption kinetics, in addition to the characteristics of the adsorbent material itself. For that purpose we use a simple Langmuir adsorption–diffusion model, which enables us to identify three dimensionless numbers that characterize the working regime of any batch adsorption experiment: an adsorption Thiele modulus, a saturation modulus, and a loading modulus. The standard models are found to be particular cases of the general adsorption–diffusion model for specific values of the dimensionless numbers. This provides sound physicochemical criteria for the validity of the models. Based on our modeling, we also propose a general yet simple data analysis procedure to practically estimate the diffusion coefficient in adsorbent pellets starting from adsorption halftimes. [less ▲]

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See detailSAXS analysis of metal dispersion in supported catalysts
Gommes, Cédric ULg

Scientific conference (2014, December)

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See detailProbabilistic models of porous materials
Gommes, Cédric ULg

Scientific conference (2014, September 19)

Hosts of natural processes and technologies depend on phenomena taking place inside nanometer-sized pores. Heterogeneous catalysis, adsorption separation processes, the weathering of porous rocks are but ... [more ▼]

Hosts of natural processes and technologies depend on phenomena taking place inside nanometer-sized pores. Heterogeneous catalysis, adsorption separation processes, the weathering of porous rocks are but a few examples. The effect of pore size on confined phenomena has been described for a long time by famous laws such as the Gibbs-Thomson and Kelvin equations. However, the underlying analyses assume geometrically perfect pores having the shape of cylinders or spheres, which is never encountered in practice. The role played by geometrical disorder in confined phenomena remains relatively unexplored. The aim of this presentation is twofold. First, we illustrate with the case of nitrogen adsorption how geometrical disorder modifies the stability of confined liquids. Second, we show that disorder per se does not rule out quantitative experimental data analysis, which we illustrate with in situ SAXS of confined liquid-liquid phase separation. In both cases the discussion is based on probabilistic models of porous materials, which is the natural mathematical tool to capture the role of geometrical disorder. [less ▲]

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See detailModeling reaction-limited Ostwald ripening of supported Ni catalysts in presence of CO: the role of particle size distribution
Gommes, Cédric ULg; Munnik, Peter; de Jongh, Petra et al

Poster (2014, March)

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