Thickness characterization toolbox for transparent protective coatings on polymer substrates

The thickness characterization of transparent protective coatings on functional, transparent materials is often problematic. In this paper, a toolbox to determine the thicknesses of a transparent coating on functional window films is presented. The toolbox consists of a combination of secondary ion mass spectrometry and profilometry and can be transferred to other transparent polymeric materials. A coating was deposited on designed model samples, which were characterized with cross-sectional views in transmission and in scanning/transmission electron microscopy and ellipsometry. The toolbox was then used to assess the thicknesses of the protective coatings on the pilot-scale window films. This coating was synthesized using straightforward sol-gel alkoxide chemistry. The kinetics of the condensation are studied in order to obtain a precursor that allows fast drying and complete condensation after simple heat treatment. The shelf life of this precursor solution was investigated in order to verify its accordance to industrial requirements. Deposition was performed successfully at low temperatures below 100 °C, which makes deposition on polymeric foils possible. By using roll-to-roll coating, the findings of this paper are easily transferrable to industrial scale. The coating was tested for scratch resistance and adhesion. Values for the emissivity (ε) of the films were recorded to justify the use of the films obtained as infrared reflective window films. In this work, it is shown that the toolbox measures similar thicknesses to those measured by electron microscopy and can be used to set a required thickness for protective coatings

Propylene metathesis over molybdenum silicate microspheres with dispersed active sites

In this work, we demonstrate that amorphous and porous molybdenum silicate microspheres are highly active catalysts for heterogeneous propylene metathesis. Homogeneous molybdenum silicate microspheres and aluminum-doped molybdenum silicate microspheres were synthesized via a nonaqueous condensation of a hybrid molybdenum biphenyldicarboxylate-based precursor solution with (3-aminopropyl)triethoxysilane. The as-prepared hybrid metallosilicate products were calcined at 500 °C to obtain amorphous and porous molybdenum silicate and aluminum-doped molybdenum silicate microspheres with highly dispersed molybdate species inserted into the silicate matrix. These catalysts contain mainly highly dispersed MoOx species, which possess high catalytic activity in heterogeneous propylene metathesis to ethylene and butene. Compared to conventional silica-supported MoOx catalysts prepared via incipient wetness impregnation (MoIWI), the microspheres with low Mo content (1.5-3.6 wt %) exhibited nearly 2 orders of magnitude higher steady-state propylene metathesis rates at 200 °C, approaching site time yields of 0.11 s-1CF CryoE; European Regional Development Fund-Project “UP CIISB, (CZ.02.1.01/0.0/0.0/18_046/0015974, LM2018110); Francqui Foundation; Grant Agency of Masaryk University, (MUNI/A/1298/2022, MUNI/J/0007/2021); U.S. Department of Energy, USDOE; Basic Energy Sciences, BES, (DE-SC0016214); Massachusetts Institute of Technology, MIT; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT, (LM2023042, RP/CPS/2022/007); Grantová Agentura České Republiky, GA ČR, (GJ20-03636Y); Central European Institute of Technology, CEITECMinistry of Education, Youth, and Sports of the Czech Republic within the INTER-EXCELLENCE II program; Ministry of Education, Youth, and Sports of the Czech Republic [RP/CPS/2022/007]; U.S. Department of Energy, Office of Basic Energy Sciences [DE-SC0016214]; European Regional Development Fund-Project "UP CIISB" [CZ.02.1.01/0.0/0.0/18_046/0015974, LM2018110]; MEYS CR [GJ20-03636Y, LM2023042]; Czech Science Foundation; Grant Agency of Masaryk University [MUNI/J/0007/2021, MUNI/A/1298/2022]; Francqui Foundation for the Francqui Research Professor chai

Aerosol Routes to Nano-structured Heterogeneous Catalysts

The technical features of aerosol processes make them highly interesting for the continuous, large scale, and tailored production of divided nanomaterials, and in particular of advanced heterogeneous (nano)catalysts.1 In addition to the “simple” aggregation of preformed particles via spray drying, reactive aerosol processes – such as the “aerosol-assisted sol-gel” process (AASG) – allow synthesizing tailored-made catalysts with tunable surface properties, textures, compositions, surface functionalities, etc.2 The method is based on the sol-gel chemistry process, possibly coupled with the evaporation-induced self-assembly (EISA) concept.3 It allows producing micronic or submicronic, inorganic or hybrid organic-inorganic particles bearing tunable and calibrated porous structures at different scales. Here, we explain why this peculiar mode of preparation has led to high-performance solid nano-catalysts in various applications including olefin metathesis,4-6 lactate synthesis,7-10 olefin epoxidation,11 (trans)-esterification.12, 13 We will also demonstrate the concept of chemo-enzymatic heterogeneous catalysts able to run cascade reactions.14, 15 Our objective is to demonstrate the tremendous possibilities offered by the coupling between bottom up sol-gel routes and aerosol processing technologies, which will arguably represent a major route of innovation not only in the field of catalyst preparation, but also more broadly in the mushrooming nanotechnology field

MoO3-based heterogeneous catalysts for the metathesis of propene

The heterogeneous metathesis of light olefins is a crucial reaction for the regulation of olefins stocks at low energy cost. Molybdenum oxide dispersed at the surface of an inorganic support is a regarded cheap and robust heterogeneous metathesis catalyst. This thesis presents fundamental and applied approaches to the understanding of the active species and to the development of new efficient catalytic materials. A systematic investigation of MoO3/SiO2-(Al2O3) catalysts with variable support composition describes the crucial role of Al. Then, the best support composition is selected and a classical wet impregnation preparation method is inspected in details. For these catalysts, the genesis of active and inactive species during the preparation is described in link with the (limited) performances reached. Alternative MoO3 deposition modes are then explored. Firstly, the wet impregnation with alternative Mo precursors (use of oxalic acid additive or use of molybdenum oxide hydrates solutions) allows impeding the formation of inactive Mo species upon calcination and produces more active catalysts. Secondly, the direct thermal spreading of MoO3 onto the support is identified as an alternative straightforward route to obtain active metathesis catalysts. An innovative non-hydrolytic sol-gel method is then implemented to prepare MoO3-SiO2-Al2O3 mixed oxides. Upon optimization of homogeneity, texture and composition, these samples turn out to be very active metathesis catalysts because highly dispersed molybdate species are stabilized at their surface.(AGRO 3) -- UCL, 201

Approches sol-gel pour la préparation de catalyseurs hétérogènes nanostructurés, hybrides et chémo-enzymatiques

Le développement de catalyseurs hétérogènes innovants est une des clés permettant d’envisager la mise en place de procédés chimiques plus efficaces et plus verts. Cet article présente les potentialités de deux approches de synthèse de matériaux catalytiques basées sur la chimie sol-gel. Par une stratégie de synthèse « brique par brique », les spécificités du sol-gel non hydrolytique et du sol-gel assisté par aérosol permettent de maîtriser les paramètres physico-chimiques clés qui dictent les performances des catalyseurs : texture, structure, composition, polarité de surface, dispersion de la phase active, hybridation avec des fonctions organiques ou des enzymes. Ceci est illustré pour une série d’applications, incluant la déshydratation d’alcools, l’hydrogénation du CO2, la valorisation de composés biosourcés, l’oxydation sélective d’alcènes, etc

PREPARATION OF POROUS CATALYSTS BY AEROSOL-ASSISTED SOL-GEL

The technical features of aerosol processes make them alluring for the continuous, large scale, and tailored production of divided nanomaterials, and in particular of advanced heterogeneous (nano)catalysts. Aside from the common aggregation of preformed particles via spray drying, reactive aerosol processes allow synthesizing tailored-made catalysts with tunable surface properties, textures, compositions, surface functionalities, etc. In the “aerosol-assisted sol-gel” process (AASG), the inorganic polycondensation reactions are confined in small droplets and happen in seconds. In addition, sol-gel reactions can be coupled with the evaporation-induced self-assembly (EISA) concept. This allows producing micronic or submicronic, inorganic or hybrid organic-inorganic particles bearing tunable and calibrated porous structures at different scales. Here, we explain why this peculiar mode of preparation has led to high-performance solid nano-catalysts in various applications including olefin metathesis, lactate synthesis, olefin epoxidation, (trans)-esterification, and dehydrogenation. In particular, we show how the method offers an excellent control over homogeneity, dispersion, surface functionalities, and texture. We will also demonstrate the concept of chemo-enzymatic heterogeneous catalysts obtained via spray techniques. Our objective is to demonstrate the tremendous possibilities offered by the coupling between bottom up sol-gel routes and aerosol processing technologies, which will arguably represent a major route of innovation not only in the field of catalyst preparation, but also more broadly in the mushrooming nanotechnology field

Combining CO2 capture and catalytic conversion to methane

Considering the global objective to mitigate climate change, import efforts are made on decreasing the net emission of CO2 from gas effluents. On the one hand CO2 capture—for example by adsorption onto solid basic materials—allows to withdraw CO2 from the waste gas streams emitted by incinerators, cement manufacture plants, combustion plants, power plants, etc. On the second hand, CO2 can be converted to useful chemicals—e.g. hydrogenation to methane—using appropriate heterogeneous catalysts. A relatively innovative strategy consists in combining both technologies by designing materials and processes which can switch between capture and methanation modes cyclically. This allows treating complex waste gas effluents by selectively and reversibly capturing CO2, and to perform the catalytic hydrogenation in appropriate reaction conditions. This short review presents the main strategies recently reported in the literature for such combined CO2 capture and methanation (CCCM) processes. We discuss the different types of reactor configurations and we present the formulations used in this context as adsorbent, as methanation catalysts, and as “dual functional materials”

Sodium Aluminate-Catalyzed Biodiesel Synthesis

Fatty acid methyl esters (FAME) were produced by transesterification of vegetable oil triglycerides, using a cheap, available, and strongly basic catalyst: NaAlO2 (sodium aluminate). Characterization revealed that NaAlO2 displays a high amount of strong basic sites, explaining its record activity compared with other common benchmark basic catalysts (calcined hydrotalcite, supported KI, and Ca and Sr oxides). Importantly, NaAlO2 operates truly as a heterogeneous catalyst and does not leach in the reaction medium. It shows good recyclability and appears more convenient than conventionally used homogeneous NaOH to treat vegetable oil, even in the presence of some free fatty acids

Room temperature synthesis of glycerol carbonate catalyzed by spray dried sodium aluminate microspheres

Nanostructured NaAlO2 microspheres are produced from an aqueous solution, by a one-pot spray drying route. The obtained solids are composed of spherical aggregates of sodium aluminate with small crystallite size and strong surface basicity. This makes them highly active catalysts in the base-catalyzed synthesis of glycerol carbonate from glycerol and dimethyl carbonate. The new catalyst does not leach and is recyclable. NaAlO2 microspheres outcompete commercially available NaAlO2 as well as other basic catalysts in the usual reaction conditions, i.e. at relatively high reaction temperature. Remarkably, the new catalyst also catalyzes efficiently the room temperature synthesis of glycerol carbonate

“Airborne” preparation of nanostructured, hybrid and chemo-enzymatic heterogeneous catalysts

Here, we present an overview of different types of nanostructured heterogeneous catalysts and we explain why this peculiar mode of preparation has allowed reaching enhanced performance in various applications including olefin metathesis,[3] ethyl lactate synthesis,[4] olefin epoxidation,[5] (trans)-esterification,[6] CO2 methanation.[7] We also describe the one-step synthesis of surface functionalized hybrid catalysts demonstrate the concept of bi-functional hybrid catalyst, active for example in the upgrading of glycerol to solketal.[8] Finally, we will turn to hybrid chemo-enzymatic heteroegenous catalysts (HCEHC), demonstrating the successful combination of a nano-zeolite and an enzyme to run chemo-enzymatic cascade reactions.[9