Preparation Of Active And Stable High-Surface Area Catalysts By Atomic Layer Deposition

Deactivation of catalytic functional oxides through the loss of surface area is a major concern. The conventional approach to maintain high-surface area of these materials is to incorporate the functional components onto a support which is less susceptible to sintering. Conventional impregnation tends to introduce large crystallites and often does not increase the surface area of the functional component. To address this issue, ALD was used in this work to engineer materials on the surface of interest. ALD has been used to form uniform oxides in a layer-by-layer manner with excellent compositional control. However, since ALD was developed in the semi-conductor industry to produce relatively thick films on a flat surface, the design criteria are very different from what is required for catalytic applications. First, the rapid cycling with high-velocity carrier gases that are commonly used in semiconductor fabrications will create diffusion limitations in porous structures. Second, when carrier gases are used, most reagents pass through the reactor without being incorporated into the sample. This is prohibitively expensive for catalytic applications. In this thesis, a static ALD system which avoids these issues was developed for preparing catalysts in two primary areas: (a) high-surface area active supports with excellent thermal stability, and (b) stabilization of precious metals. The first area involved fabricating thin films of Fe2O3, CeO2, CeZrO4, and LaFeO3 on porous Al2O3. These high-surface area films were shown to be uniform and they exhibited excellent thermal stability up to 1273 K when used as supports for Pd in methane and CO oxidation. With compositional control by ALD, CeZrO4 and LaFeO3, complex oxides would otherwise require complex synthesis or high temperature treatments, were easily fabricated at moderate conditions. The second area involved stabilizing metal particles by thin films of LaFeO3 and ZrO2 prepared by ALD. Pd supported on LaFeO3 is of interests as it is the classical example of a “smart” catalyst capable of redispersing metal particles following redox cycling conditions. The LaFeO3 catalysts were shown to exhibit properties expect for smart catalysts. Overcoating thin films of ZrO2 on Pd to improve its thermal stability was also demonstrated

Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation

Atomic layer deposition (ALD) offers exciting possibilities for controlling the structure and composition of surfaces on the atomic scale in heterogeneous catalysts and solid oxide fuel cell (SOFC) electrodes. However, while ALD procedures and equipment are well developed for applications involving flat surfaces, the conditions required for ALD in porous materials with a large surface area need to be very different. The materials (e.g., rare earths and other functional oxides) that are of interest for catalytic applications will also be different. For flat surfaces, rapid cycling, enabled by high carrier-gas flow rates, is necessary in order to rapidly grow thicker films. By contrast, ALD films in porous materials rarely need to be more than 1 nm thick. The elimination of diffusion gradients, efficient use of precursors, and ligand removal with less reactive precursors are the major factors that need to be controlled. In this review, criteria will be outlined for the successful use of ALD in porous materials. Examples of opportunities for using ALD to modify heterogeneous catalysts and SOFC electrodes will be given

Modification of LSF-YSZ Composite Cathodes by Atomic Layer Deposition

composite, Solid-Oxide-Fuel-Cell (SOFC) electrodes of La0.8Sr0.2FeO3 (LSF) and yttria-stabilized zirconia (YSZ) were prepared by infiltration methods and then modified by Atomic Layer Deposition (ALD) of ZrO2, La2O3, Fe2O3, or La2O3-Fe2O3 codeposited films of different thicknesses to determine the effect of surface composition on cathode performance. Film growth rates for ALD performed using vacuum procedures at 573 K for Fe2O3 and 523 K for ZrO2 and La2O3 were determined to be 0.024 nm ZrO2/cycle, 0.019 nm La2O3/cycle, and 0.018 nm Fe2O3/cycle. For ZrO2 and Fe2O3, impedance spectra on symmetric cells at 873 K indicated that polarization resistances increased with coverage in a manner suggesting simple blocking of O2 adsorption sites. With La2O3, the polarization resistance decreased with small numbers of ALD cycles before again increasing at higher coverages. When La2O3 and Fe2O3 were co-deposited, the polarization resistances remained low at high film coverages, implying that O2 adsorption sites were formed on the co-deposited films. The implications fo these results for future SOFC electrode development are discussed

Towards exploratory hypothesis testing and analysis

10.1109/ICDE.2011.5767907Proceedings - International Conference on Data Engineering745-75

Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation

Atomic layer deposition (ALD) offers exciting possibilities for controlling the structure and composition of surfaces on the atomic scale in heterogeneous catalysts and solid oxide fuel cell (SOFC) electrodes. However, while ALD procedures and equipment are well developed for applications involving flat surfaces, the conditions required for ALD in porous materials with a large surface area need to be very different. The materials (e.g., rare earths and other functional oxides) that are of interest for catalytic applications will also be different. For flat surfaces, rapid cycling, enabled by high carrier-gas flow rates, is necessary in order to rapidly grow thicker films. By contrast, ALD films in porous materials rarely need to be more than 1 nm thick. The elimination of diffusion gradients, efficient use of precursors, and ligand removal with less reactive precursors are the major factors that need to be controlled. In this review, criteria will be outlined for the successful use of ALD in porous materials. Examples of opportunities for using ALD to modify heterogeneous catalysts and SOFC electrodes will be given

Oil Media on Paper: Investigating the Effect of Linseed Oils on Pure Cellulosic Paper Supports. A Research Matter of Damage Assessment

Oil media on paper, such as oil paintings, sketches, prints, and books, occasionally present problems associated with the effect of oil medium on the paper support, raising a composite matter of condition assessment as it depends on several factors. The present work examines the effect of linseed oil on paper and, in particular, the changes caused by three types of linseed oil on the optical, morphological, mechanical, and chemical properties of pure cellulosic paper, employing mock-ups submitted to artificial ageing in controlled conditions of relative humidity and temperature in airtight vessels. The study involved colorimetry, opacity, tensile strength, pH measurements, SEM, FTIR, and VOC analysis with GC-MS. Processing of the results has so far indicated that thermal-humid ageing caused the gradual darkening of the oil-impregnated mock-ups, as well as alterations in opacity, intense fall of pH values, and severe reductions in tensile strength, while linseed oil processing during manufacture has a significant impact. FTIR spectra have indicated that chemical changes upon ageing are in accordance with those of optical and mechanical changes, while VOC emissions are mostly associated with the drying and degradation of the different types of linseed oil

Oil Media on Paper: Investigating the Effect of Linseed Oils on Lignocellulosic Paper Supports

Condition assessment of works of art created with oil media on paper could be a complex matter when presenting problems of damage due to the absorption of oil binders by the paper support, since they depend on several factors and occur in variable conditions. The present work refers to the results of an investigation on the effect of linseed oils on the color, opacity, morphology, tensile strength, and chemical properties of lignocellulosic papers, in comparison to that of pure cellulosic papers. Lignocellulosic papers are involved in research on new, yet significant, parameters that might influence the behavior of the oil-impregnated areas of the supports upon aging. The research was applied to mock-ups, made of two types of lignocellulosic paper impregnated with three types of linseed oil and subjected to accelaratated ageing in specific conditions of relative humidity and temperature in closed environment. The research involved colorimetry, opacity, tensile strength, pH measurements, SEM, FTIR, and VOC analysis with GC-MS. The results indicated that thermal-humid ageing caused the gradual darkening of the oil-impregnated mock-ups, alterations in opacity, and decrease of pH values, depending mainly on the formulation of linseed oil, as well as a reduction in tensile strength. FTIR analysis results indicated that the chemical changes that occur upon ageing supported the recorded optical and mechanical alterations, while VOC emissions are both associated with the paper type and the kinetics of degradation of the different types of linseed oil

High-surface-area, iron-oxide films prepared by atomic layer deposition on \u3b3-Al2O3

High-surface-area iron oxides were prepared by Atomic Layer Deposition (ALD) on 130-m(2)/g gamma-Al2O3 for use as a catalyst support. Measurements of the sample mass, surface area, and pore-size distribution as a function of the number of ferrocene-O-2 ALD cycles at 623 K suggested that the iron oxide grew as a dense, conformal film with a growth rate similar to 0.016-nm per cycle. While films with 20 ALD cycles (20Fe(2)O(3)Al(2)O(3), 0.25 g Fe2O3/g Al2O3) were difficult to distinguish by HAADF STEM, EDS mapping indicated the Al2O3 was uniformly coated. Raman Spectroscopy showed the films were in the form of Fe2O3; but XRD measurements on samples with as many as 100 ALD cycles (100Fe(2)O(3)-Al2O3, 0.84g Fe2O3/g Al2O3) showed no evidence for crystalline iron-oxide phases, even after calcination at 1073 K. Specific rates for the water-gas-shift (WGS) reaction on the ALD-coated samples were significantly lower than those on bulk Fe2O3. However, addition of 1 wt.% Pd to Fe2O3/Al2O3 supports prepared by ALD exhibited specific rates that were much higher than that observed when I wt.% Pd was added to Fe2O3/Al2O3 prepared by conventional impregnation of Fe salts, suggesting more uniform contact between the Pd and FeOx phases on samples prepared by ALD

Investigation of the Thermodynamic Properties of Surface Ceria and Ceria–Zirconia Solid Solution Films Prepared by Atomic Layer Deposition on Al2O3

The properties of 20 wt % CeO2 and 21 wt % Ce0.5Zr0.5O2 films, deposited onto a γ-Al2O3 by Atomic Layer Deposition (ALD), were compared to bulk Ce0.5Zr0.5O2 and γ-Al2O3-supported samples on which 20 wt % CeO2 or 21 wt % CeO2–ZrO2 were deposited by impregnation. Following calcination to 1073 K, the ALD-prepared catalysts showed much lower XRD peak intensities, implying that these samples existed as thin films, rather than larger crystallites. Following the addition of 1 wt % Pd to each of the supports, the ALD-prepared samples exhibited much higher rates for CO oxidation due to better interfacial contact between the Pd and ceria-containing phases. The redox properties of the ALD samples and bulk Ce0.5Zr0.5O2 were measured by determining the oxidation state of the ceria as a function of the H2:H2O ratio using flow titration and coulometric titration. The 20 wt % CeO2 ALD film exhibited similar thermodynamics to that measured previously for a sample prepared by impregnation. However, the sample with 21 wt % Ce0.5Zr0.5O2 on γ-Al2O3 reduced at a much higher P O 2 and showed evidence for transition between the Ce0.5Zr0.5O2 and Ce0.5Zr0.5O1.75 phases