Michaela Klotz

Substrates do influence the ordering of mesoporous thin films

Two kinds of ordered structures, a cylindrical hexagonal and a compact hexagonal arrangement of micelles, were synthesized using either CTAB or a Pluronic block copolymer as templating agents. The ordering of thin films deposited on glass, dielectrics (Si3N4, SiTiOx) and a metal with a native oxide (Ti) were compared. We observed that the ordered texture of the films was greatly influenced by the substrate. In order to differentiate the effects of surface roughness and surface forces, glass substrates were systematically modified by grafting ethylene oxide/propylene oxide (EO/PO) statistical copolymers. Varying the EO content allowed fine tuning of the hydrophilicity of the surface. In this case, the same phase and quality of ordering as on bare glass is observed but with a systematic higher contraction of the ordered structure. This is ascribed to the similar chemical nature between the grafted substrate and the templating molecules, which fasten the formation of the ordered structure.

Porous alumina thin layers using mesophase templating

A method of preparation for alumina thin layers exhibiting an ordered mesoporosity is presented. The synthesis conditions are discussed and the resulting layers are characterised.

Mixed Ionic–Electronic Conducting Catalysts for Catalysed Gasoline Particulate Filters

A catalyst based on Pd and Rh nanoparticles supported on a Gadolinia-Doped Ceria support, a mixed O2−/e− ionic electronic conductor (MIEC), has been prepared and washcoated in SiC catalyzed gasoline particulate filters (cGPF) prototypes. These filters have been prepared and tested for the aftertreatment of gasoline direct injection engine exhausts. Catalytic performances of various configurations of cGPFs (different catalyst loadings and locations) have been carried out near real conditions and compared with those of a commercial three-way converter TC as well as a monolith washcoated with the same MIEC-supported catalyst. Among all the samples tested, the most promising one is a GPF equipped with a SiC filtration membrane on which a catalytic layer has been washcoated. This cGPF combines good filtering efficiency, due to the membrane, and remarkable catalytic performances in presence of soot and water. The catalytic performance is greater than those of a commercial TC, in spite of a 9 times lower platinum group metal loading. This is attributed to both self-sustained electrochemical promotion and a higher availability of the active sites localized on the membrane.

High specific surface area YSZ powders from a supercritical CO2 process as catalytic supports for NOx storage–reduction reaction

Nanometric yttria-stabilized zirconia (3 mol% yttria, SC-3YSZ) was synthesized using an innovative supercritical carbon dioxide-aided sol–gel process and used as a support for NOx storage catalysts. Wash-coats composed of noble metals (Pt and Rh) dispersed on 3YSZ were deposited inside the porosity of mini-diesel particulate filters. Commercial and SC-3YSZ powders were used as supports independently and mixed. NOx storage/reduction performances were compared under cycling conditions according to the YSZ support surface area, the washcoat localization inside the DPF and the metallic dispersions. All the results emphasize that the presence of high specific surface area SC-3YSZ inside the DPF improves the NOx conversion, the N2 selectivity and the NOx storage capacity. This enhancement of the catalytic properties was linked with the increase in both the metallic dispersion and the number of storage sites on the catalyst surface.

Kinetic Accessibility of Porous Material Adsorption Sites Studied through the Lattice Boltzmann Method

We present here a computational model based on the lattice Boltzmann scheme to investigate the accessibility of active adsorption sites in hierarchical porous materials to adsorbates in a flowing liquid. By studying the transport and adsorption of tracers after they enter the pore space of the virtual sample, we characterize their kinetics as they pass through the pore space and adsorb on the solid-liquid interface. The model is validated on simple geometries with a known analytical solution. We then use it to investigate the influence of regular grooves or disordered roughness on the walls of a slit pore geometry, looking at the impact on adsorption and transport. In particular, we highlight the importance of adsorption site accessibility, which depends on the shape and connectivity of the pore space as well as the fluid flow profile and velocity.

Effect of the Reduction Step on the Catalytic Performance of Pd–CeMO2 Based Catalysts (M = Gd, Zr) for Propane Combustion

The effect of a reduction step on the catalytic activity of Pd supported doped ceria catalysts was investigated for the propane combustion. Two different oxides based on ceria zirconia (CZ), as a reference three-way catalyst support, and Gadolinia doped ceria (GDC), a mixed ionic electronic conductor, have been used to support Pd nanoparticles. The samples were characterized by H2–CO chemisorption, temperature programmed reduction, and XPS. In addition, the reduction step in H2 was in situ observed by environmental transmission electron microscopy. It was found that the catalytic activity of Pd supported on ceria-based supports can be strongly promoted by a reduction step whereas it does not change on alumina. This effect was attributed, in particular on GDC, to the reduction of a surface interaction phase, PdxCeO2−δ, which induces a re-dispersion of metallic Pd nanoparticles.

How can nanoparticles change the mechanical resistance of ordered mesoporous thin films

Abstract Nanoindentation was performed on mesoporous thin films in order to investigate their mechanical behaviour. It has been found that the empty mesoporous films behave plastically while films filled with nanoparticles exhibit more elastic deformations. This contrasting behaviour is consistent with the different indent morphologies observed by optical and electronic microscopy.

Synthesis and Texture of Mesophase Templated Silica Layers Seeded with Nanoparticles

Mesophase templated silica layers seeded with magnetic or non magnetic nanoparticles are prepared. The study of the interactions between the nanoparticles and the others compounds of the synthesis solution is first described to explain the synthesis conditions allowing a homogeneous seeding. X-ray diffraction measurements are then used to study the texture of thick layers seeded with magnetic nanoparticles.

Synthesis of Functional Ceramic Supports by Ice Templating and Atomic Layer Deposition

In this work, we report an innovative route for the manufacturing of functional ceramic supports, by combining ice templating of yttria stabilized zirconia (YSZ) and atomic layer deposition (ALD) of Al2O3 processes. Ceramic YSZ monoliths are prepared using the ice-templating process, which is based on the controlled crystallization of water following a thermal gradient. Sublimation of the ice and the sintering of the material reveal the straight micrometer sized pores shaped by the ice crystal growth. The high temperature sintering allows for the ceramic materials to present excellent mechanical strength and porosities of 67%. Next, the conformality benefit of ALD is used to deposit an alumina coating at the surface of the YSZ pores, in order to obtain a functional material. The Al2O3 thin films obtained by ALD are 100 nm thick and conformally deposited within the macroporous ceramic supports, as shown by SEM and EDS analysis. Mercury intrusion experiments revealed a reduction of the entrance pore diameter, in line with the growth per cycle of 2 A of the ALD process. In addition to the manufacture of the innovative ceramic nanomaterials, this article also describes the fine characterization of the coatings obtained using mercury intrusion, SEM and XRD analysis.