Maria Paulis

Catalytic combustion of volatile organic compounds on Au/CeO2/Al2O3 and Au/Al2O3 catalysts

Catalytic oxidation of n-hexane, benzene and 2-propanol was investigated on Au/CeO2/Al2O3 and Au/Al2O3 catalysts prepared from the deposition–precipitation method and characterised by XRD, scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–VIS and X-ray photoelectron spectroscopy (XPS) techniques. It is shown that ceria enhances the fixation and final dispersion of gold particles, leading to stabilise them in lower crystallite sizes. Catalytic results show that ceria improves the activity of gold particles in the oxidation of the tested volatile organic compounds (VOCs), probably by increasing the mobility of the lattice oxygen and controlling and maintaining the adequate oxidation state of the active gold particles.

Deep oxidation of VOC mixtures with platinum supported on Al2O3/Al monoliths

Abstract Pt impregnated metallic monoliths prepared from anodised aluminium foils were tested to study their catalytic activity in complete oxidation of volatile organic compound (VOC) mixtures. The VOCs oxidised were 2-propanol, toluene, methyl ethyl ketone (MEK), acetone and their mixtures. Complete oxidation was obtained in all cases except for the case of 2-propanol, where acetone was found as an oxidation intermediate. Even if the adsorption of the VOC on the Al 2 O 3 is governed by its polarity, the reactivity is mainly affected by the competition of the oxygen atoms chemisorbed on the Pt particles.

Influence of the surface adsorption–desorption processes on the ignition curves of volatile organic compounds (VOCs) complete oxidation over supported catalysts

Abstract The simplicity to obtain ignition curves has resulted in their extended use for the measurement of the catalysts activity in the complete oxidation of VOCs. However, we have found that this method gives incorrect results for some systems, such as conversions greater than 100% or disagreements between the conversion values calculated through the concentration change of the reactants and the products, which can lead to misunderstandings. Toluene oxidation over reduced Pd/Al 2 O 3 and acetone oxidation over supported Mn 2 O 3 have presented those features. The study of these systems has been carried out performing DRIFTS spectra under reaction conditions and TPD experiments. The effect of the start-up procedure of the complete oxidation reactions has been considered as well. After discarding the formation of partial oxidation products and the hydrogen retention on Pd as possible causes, the adsorption–desorption processes of VOCs, surface intermediates and CO 2 were considered. It can be concluded that when the activity of the active phase supported on the Al 2 O 3 is high enough to allow the coupling at relatively low temperature of combustion with the adsorption and desorption processes of toluene or acetone and CO 2 , a sort of chain reaction occurs leading to CO 2 peaks.

Preparation and characterization of niobium oxide for the catalytic aldol condensation of acetone

Niobium oxide (Nb2O5) has been prepared from a precursor solution of NbCl5 in ethanol. The effect of pH, water content for hydrolysis and calcination temperature on microstructural, spectroscopic and acidic properties has been studied using N2 adsorption, X-ray diffraction (XRD), FTIR spectroscopy, temperature programmed desorption (TPD) of ammonia and DRIFTS of adsorbed ammonia. The activity for the aldol condensation of acetone was studied as well.

UV screening clear coats based on encapsulated CeO2 hybrid latexes

CeO2 nanoparticles have been successfully incorporated into acrylic latex particles with an excellent homogeneous distribution (mostly one inorganic particle per polymer particle) and limited aggregation (inorganic nanoparticles predominantly in the 17–26 nm range, when the original cerium oxide dispersion had a volume average diameter of 8 nm). The hydrophobicity and wettability of the inorganic nanoparticles with the monomer mixture and the process used, semibatch emulsion polymerization on a seed produced by miniemulsion polymerization containing the whole load of the metal oxide, were the key aspects to achieve this morphology for the first time at industrially relevant solids content (40 wt%). Furthermore, the transparency and the substantially enhanced UV-Vis absorbance capacity make those hybrid acrylic/CeO2 dispersions excellent candidates for a large number of applications including clear coatings and cosmetics.

Preparation of Al2O3/Al monoliths by anodisation of aluminium as structured catalytic supports

The different variables of the aluminium anodisation process, anodisation time, current density, electrolyte nature, its temperature and concentration, and the effect of agitation, and their effects on the final alumina textural properties have been studied. Characterisation of the alumina generated by anodisation has been carried out by N2 adsorption, SEM and gravimetry. It has been observed that the texture of the coating depends on two main processes taking place during aluminium anodisation: alumina generation and its dissolution. The proper combination of both processes, given by the choice of the different process variables, will produce an adherent alumina layer with excellent properties to produce catalytic devices based on alumina on aluminium monoliths.

Modeling the equilibrium morphology of nanodroplets in the presence of nanofillers

Waterborne polymer nanocomposites containing carbon nanotubes, clay platelets, laponite disks and other spherical/nonspherical nanofillers have been the focus of many recent investigations. The miniemulsion polymerization has proved to be a powerful technique to create new hybrid waterborne nanocomposites with enhanced properties. It is necessary to understand how the nanofiller shape/size and its compatibility with the phases affects the equilibrium morphology of the polymer nanoparticle to control the morphology and the properties of the resulting polymeric dispersions. With the aid of Monte Carlo simulations, the equilibrium morphology of hybrid monomer nanodroplets in the presence of nanofillers with different characteristics was obtained. A series of morphology maps depending on the nanofiller compatibility with the monomer and water phases and its shape have been obtained. These new maps may help to design and determine the required conditions to synthesize innovative waterborne polymer nanocomposites with specific morphologies through miniemulsion polymerization.

Morphology and properties of waterborne adhesives made from hybrid polyacrylic/montmorillonite clay colloidal dispersions showing improved tack and shear resistance

AbstractThe morphology and adhesive properties of waterborne films from n-butyl acrylate/methyl methacrylate/montmorillonite clay hybrid polymer latexes which were synthesized by miniemulsion polymerization in the presence of a reactive organoclay ((2-methacryloylethyl) hexadecyldimethylammonium modified montmorillonite, CMA16) were investigated. It was found by cryo-TEM analysis that the hybrid dispersions were a mixture of colloidal particles composed of a small fraction of free montmorillonite clay platelets, polymer latex particles, polymer particles to which one or more clay platelets where adhered onto its surface and a fraction of colloidal material consisted of a clay platelet with a polymer lob adhered to either side, in other words hybrid particles with a dumbbell-like morphology. The films made from these waterborne hybrid dispersions presented a homogeneous dispersion of the clay platelets and exfoliated morphology. The shear adhesion failure temperature (SAFT) and shear resistance of the hybrid latex films synthesized with CMA16 were better than those prepared with a commercial clay (Cloisite 30B), but presented a liquid-like probe-tack performance. When allyl methacrylate (AMA) was added in the formulation, SAFT and shear resistance improved, but the film had a very low energy of adhesion due to the excessively crosslinked matrix. In order to reduce crosslink density and thus improve the adhesion energy, small amounts of chain transfer agent, in this case n-dodecyl mercaptan (n-DDM), were used in the miniemulsion polymerization process. Adhesive films made from these waterborne hybrid dispersions showed excellent SAFT and shear resistance, and good energy of adhesion.

Surfactant-Free Miniemulsion Polymerization of n-BA/S Stabilized by NaMMT: Films with Improved Water Resistance

The use of sodium montmorillonite clay as a stabilizer in the surfactant-free emulsion polymerization of n-butyl acrylate/styrene (n-BA/S) was assessed. It was shown that the use of the clay alone did not yield the desired armored latex particles. A functional comonomer, that is, a phosphate ester of poly(ethylene glycol) monomethacrylate, was used to improve the interaction between the polymer and clay, thus allowing for the clay platelets to adhere to the surface of the polymer particles. The morphology of the films obtained for these two different scenarios was similar and resembled a honeycomb structure. However, their water-resistance properties differed drastically. The water absorption and water vapor permeation rate were much lower in the hybrid n-BA/S/clay films in the presence of the functional monomer than in the films obtained without the functional monomer.

High-performance adhesives resulting from spontaneous formation of nanogels within miniemulsion particles.

Molecular structure plays a crucial role in determining the final properties of pressure-sensitive adhesives. Here, we demonstrate that the molecular structure of polyurethane/(meth)acrylic hybrids synthesized by miniemulsion photopolymerization changes during storage of the dispersion at room temperature because of the spontaneous formation of nanogels by the assembly of polymer chains within the polymer particles. Analysis of the nanogel structure by asymmetric-flow field-flow fractionation allows identification of the molecular structure that provides the unusual combination of high tack adhesion and excellent shear resistance at high temperature [maximum value of the shear-adhesion failure temperature (SAFT) test, >210 °C].