Browsing by Author "Puurunen, Riikka L."
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Item Aqueous-phase reforming of Fischer-Tropsch alcohols over nickel-based catalysts to produce hydrogen: Product distribution and reaction pathways(2018-10-25) Coronado, Irene; Pitínová, Martina; Karinen, Reetta; Reinikainen, Matti; Puurunen, Riikka L.; Lehtonen, Juha; Department of Chemical and Metallurgical Engineering; Catalysis; VTT Technical Research Centre of Finland; Aalto UniversityCatalytic aqueous-phase reforming (APR) can be applied to process the organic compounds in the water fractions derived from the Fischer-Tropsch (FT) synthesis. This work aimed at finding an active nickel-based catalyst to convert organic compounds typically found in FT-derived waters, such as alcohols, into hydrogen. In addition, this work aimed at proposing potential reaction pathways that explain the product distribution resulting from the APR of C1–C3 alcohols. Solutions with 5% mass fraction of either methanol, ethanol, propan-1-ol or propan-2-ol in water were processed in APR at 230 °C and 3.2 MPa over different nickel-based catalysts in a continuous packed-bed reactor. Methanol was successfully reformed into hydrogen and carbon monoxide with conversions up to 60%. The conversion of C2–C3 alcohols achieved values in the range of 12% to 55%. The results obtained in the APR of C2–C3 alcohols suggest that in addition to reforming to hydrogen and carbon monoxide, the alcohols underwent dehydrogenation and decarbonylation. The most stable catalyst, nickel-copper supported on ceria-zirconia, reached feedstock conversions between 20% and 60% and high hydrogen selectivity. Monometallic nickel supported on ceria-zirconia catalysts reached higher H2 yields; however, the yield of side products, such as alkanes, was also higher over the monometallic catalysts. Accordingly, ceria-zirconia nickel-based supported catalysts constitute suitable candidates to process the alcohols in the water fractions derived from the FT synthesis.Item An atomic layer deposition diffusion-reaction model for porous media with different particle geometries(Royal Society of Chemistry, 2024-03-07) Heikkinen, Niko; Lehtonen, Juha; Puurunen, Riikka L.; Department of Chemical and Metallurgical Engineering; CatalysisThis work presents a diffusion-reaction model for atomic layer deposition (ALD), which has been adapted to describe radial direction reactant transport and adsorption kinetics in a porous particle. Specifically, we present the effect of three particle geometries: spherical, cylindrical and a slab in the diffusion-reaction model. The reactant diffusion propagates as a unidimensional front inside the slab particle, whereas with cylinder and spherical particles, the reactant diffusion approaches the particle centre from two and three dimensions, respectively. Due to additional reactant propagation dimensions, cylindrical and spherical particles require less exposure for full particle penetration. In addition to the particle geometry effect, a sensitivity analysis was used to compare the impact of the particles’ physical properties on the achieved penetration depth. The analysis evaluates properties, such as the combined porosity and tortuosity factor, mean pore diameter, specific surface area, pore volume, and particle radius. Furthermore, we address the impact of the reactant molar mass, growth-per-cycle (GPC), sticking probability, reactant exposure and deposition temperature on the simulated diffusion and surface coverage profiles. The diffusion-reaction model presented in this work is relevant for the design and optimization of ALD processes in porous media with different particle geometries.Item Atomic Layer Deposition of Zinc Oxide on Mesoporous Zirconia Using Zinc(II) Acetylacetonate and Air(American Chemical Society, 2023-10-10) Yim, Jihong; Haimi, Eero; Mäntymäki, Miia; Kärkäs, Ville; Bes, René; Arandia Gutierrez, Aitor; Meinander, Kristoffer; Brüner, Philipp; Grehl, Thomas; Gell, Lars; Viinikainen, Tiia; Honkala, Karoliina; Huotari, Simo; Karinen, Reetta; Putkonen, Matti; Puurunen, Riikka L.; Department of Chemical and Metallurgical Engineering; School common, CHEM; Department of Bioproducts and Biosystems; Catalysis; School common, CHEM; Aalto University; IONTOF GmbH; University of Jyväskylä; University of HelsinkiThe self-terminating chemistry of atomic layer deposition (ALD) ideally enables the growth of homogeneously distributed materials on the atomic scale. This study investigates the ALD of zinc oxide (ZnO) on mesoporous zirconium oxide (ZrO2) using zinc acetylacetonate [Zn(acac)2] and synthetic air in a fixed-bed powder ALD reactor. A broad variety of methods, including thermogravimetry analysis, scanning electron microscopy with energy-dispersive X-ray spectroscopy, low-energy ion scattering, X-ray absorption near-edge structure, X-ray photoelectron spectroscopy, in-situ diffuse reflectance infrared Fourier transform spectroscopy-mass spectrometry, and density functional theory calculations, were used to analyze the reactant and the resulting samples. The factors affecting the zinc loading (wt %) on ZrO2 were investigated by varying the ALD reaction temperature (160-240 °C), the calcination temperature of zirconium oxide (400-1000 °C), and the ALD cycle number (up to three). The studied process showed self-terminating behavior with the areal number density of zinc of approximately two atoms per square nanometer per cycle. Zinc was distributed throughout ZrO2. After the Zn(acac)2 reaction, acac ligands were removed using synthetic air at 500 °C. In the following cycles, already-deposited ZnO acted as nuclei for further ZnO growth. This study demonstrates the potential of Zn(acac)2 as an ALD reactant and provides an initial understanding of ZnO growth via ALD on high surface area porous particles as an example for catalytic applications.Item Comparison of mechanical properties and composition of magnetron sputter and plasma enhanced atomic layer deposition aluminum nitride films(2018-09-01) Sippola, Perttu; Pyymaki Perros, Alexander; Ylivaara, Oili M.E.; Ronkainen, Helena; Julin, Jaakko; Liu, Xuwen; Sajavaara, Timo; Etula, Jarkko; Lipsanen, Harri; Puurunen, Riikka L.; Department of Electronics and Nanoengineering; VTT Technical Research Centre of Finland; University of Jyväskylä; Department of Chemical and Metallurgical Engineering; Department of Chemistry and Materials ScienceA comparative study of mechanical properties and elemental and structural composition was made for aluminum nitride thin films deposited with reactive magnetron sputtering and plasma enhanced atomic layer deposition (PEALD). The sputtered films were deposited on Si (100), Mo (110), and Al (111) oriented substrates to study the effect of substrate texture on film properties. For the PEALD trimethylaluminum-ammonia films, the effects of process parameters, such as temperature, bias voltage, and plasma gas (ammonia versus N2/H2), on the AlN properties were studied. All the AlN films had a nominal thickness of 100 nm. Time-of-flight elastic recoil detection analysis showed the sputtered films to have lower impurity concentration with an Al/N ratio of 0.95, while the Al/N ratio for the PEALD films was 0.81-0.90. The mass densities were ∼3.10 and ∼2.70 g/cm3 for sputtered and PEALD AlN, respectively. The sputtered films were found to have higher degrees of preferential crystallinity, whereas the PEALD films were more polycrystalline as determined by x-ray diffraction. Nanoindentation experiments showed the elastic modulus and hardness to be 250 and 22 GPa, respectively, for sputtered AlN on the (110) substrate, whereas with PEALD AlN, values of 180 and 19 GPa, respectively, were obtained. The sputtered films were under tensile residual stress (61-421 MPa), whereas the PEALD films had a residual stress ranging from tensile to compressive (846 to −47 MPa), and high plasma bias resulted in compressive films. The adhesion of both films was good on Si, although sputtered films showed more inconsistent critical load behavior. Also, the substrate underneath the sputtered AlN did not withstand high wear forces as with the PEALD AlN. The coefficient of friction was determined to be ∼0.2 for both AlN types, and their wear characteristics were almost identical.Item Competitive Hydrodeoxygenation and Hydrodenitrogenation Reactions in the Hydrotreatment of Fatty Acid and Amine Mixtures(Springer, 2023-10) Verkama, Emma; Auvinen, Paavo; Albersberger, Sylvia; Tiitta, Marja; Karinen, Reetta; Puurunen, Riikka L.; Department of Chemical and Metallurgical Engineering; Catalysis; Neste CorporationUnderstanding how hydrotreating oxygen-containing compounds together with nitrogen-containing compounds affects the reactivity and selectivity is relevant for processing renewable feedstocks. In this work, competitive hydrodeoxygenation (HDO) and hydrodenitrogenation (HDN) reactions were studied by co-hydrotreating palmitic acid (C16 acid) and tetradecylamine (C14 amine) over a Pt/ZrO2 catalyst in a batch reactor. HDO proceeded faster than HDN in the studied system, and the deoxygenation reactions were found to have an inhibitory effect on HDN. Co-hydrotreating the C16 acid and the C14 amine expanded the reaction network from the individual HDO and HDN networks and changed the prevailing reaction pathways, initially in favor of oxygen removal. The formation of heavy secondary amides and amines through condensation reactions became increasingly favored as the share of C16 acid in the feed increased. For a given conversion level, the condensation product selectivity was observed to increase as the reaction temperature was decreased, whereas increasing the reaction temperature promoted the formation of the desired paraffins. This work described the ease of HDO compared to HDN, the role of condensation reactions in the co-hydrotreating reaction network, and the inhibitory effect on HDN thereof.Item Conformality in atomic layer deposition: Current status overview of analysis and modelling(AMERICAN INSTITUTE OF PHYSICS, 2019-06-01) Cremers, Véronique; Puurunen, Riikka L.; Dendooven, Jolien; Department of Chemical and Metallurgical Engineering; Catalysis; Ghent UniversityAtomic layer deposition (ALD) relies on alternated, self-limiting reactions between gaseous reactants and an exposed solid surface to deposit highly conformal coatings with a thickness controlled at the submonolayer level. These advantages have rendered ALD a mainstream technique in microelectronics and have triggered growing interest in ALD for a variety of nanotechnology applications, including energy technologies. Often, the choice for ALD is related to the need for a conformal coating on a 3D nanostructured surface, making the conformality of ALD processes a key factor in actual applications. In this work, we aim to review the current status of knowledge about the conformality of ALD processes. We describe the basic concepts related to the conformality of ALD, including an overview of relevant gas transport regimes, definitions of exposure and sticking probability, and a distinction between different ALD growth types observed in high aspect ratio structures. In addition, aiming for a more standardized and direct comparison of reported results concerning the conformality of ALD processes, we propose a new concept, Equivalent Aspect Ratio (EAR), to describe 3D substrates and introduce standard ways to express thin film conformality. Other than the conventional aspect ratio, the EAR provides a measure for the ease of coatability by referring to a cylindrical hole as the reference structure. The different types of high aspect ratio structures and characterization approaches that have been used for quantifying the conformality of ALD processes are reviewed. The published experimental data on the conformality of thermal, plasma-enhanced, and ozone-based ALD processes are tabulated and discussed. Besides discussing the experimental results of conformality of ALD, we will also give an overview of the reported models for simulating the conformality of ALD. The different classes of models are discussed with special attention for the key assumptions typically used in the different modelling approaches. The influence of certain assumptions on simulated deposition thickness profiles is illustrated and discussed with the aim of shedding light on how deposition thickness profiles can provide insights into factors governing the surface chemistry of ALD processes. We hope that this review can serve as a starting point and reference work for new and expert researchers interested in the conformality of ALD and, at the same time, will trigger new research to further improve our understanding of this famous characteristic of ALD processes.Item Conformality of atomic layer deposition in microchannels: impact of process parameters on the simulated thickness profile(ROYAL SOC CHEMISTRY, 2022-03-11) Yim, Jihong; Verkama, Emma; Velasco, Jorge A.; Arts, Karsten; Puurunen, Riikka L.; Department of Chemical and Metallurgical Engineering; Catalysis; Eindhoven University of TechnologyUnparalleled conformality is driving ever new applications for atomic layer deposition (ALD), a thin film growth method based on repeated self-terminating gas-solid reactions. In this work, we re-implemented a diffusion-reaction model from the literature to simulate the propagation of film growth in wide microchannels and used that model to explore trends in both the thickness profile as a function of process parameters and different diffusion regimes. In the model, partial pressure of the ALD reactant was analytically approximated. Simulations were made as a function of kinetic and process parameters such as the temperature, (lumped) sticking coefficient, molar mass of the ALD reactant, reactant's exposure time and pressure, total pressure, density of the grown material, and growth per cycle (GPC) of the ALD process. Increasing the molar mass and the GPC, for example, resulted in a decreasing penetration depth into the microchannel. The influence of the mass and size of the inert gas molecules on the thickness profile depended on the diffusion regime (free molecular flow vs. transition flow). The modelling was compared to a recent slope method to extract the sticking coefficient. The slope method gave systematically somewhat higher sticking coefficient values compared to the input sticking coefficient values; the potential reasons behind the observed differences are discussed.Item Effect of atomic layer deposited zinc promoter on the activity of copper-on-zirconia catalysts in the hydrogenation of carbon dioxide to methanol(Elsevier BV, 2023-02) Arandia, Aitor; Yim, Jihong; Warraich, Hassaan; Leppäkangas, Emilia; Bes, René; Lempelto, Aku; Gell, Lars; Jiang, Hua; Meinander, Kristoffer; Viinikainen, Tiia; Huotari, Simo; Honkala, Karoliina; Puurunen, Riikka L.; Department of Chemical and Metallurgical Engineering; Department of Applied Physics; OtaNano; Department of Bioproducts and Biosystems; Catalysis; NanoMaterials; Department of Chemical and Metallurgical Engineering; University of Jyväskylä; University of Helsinki; Helsinki Institute of PhysicsThe development of active catalysts for carbon dioxide (CO2) hydrogenation to methanol is intimately related to the creation of effective metal-oxide interfaces. In this work, we investigated how the order of addition of copper and zinc on zirconia influences the catalytic properties, the catalytic activity and selectivity toward methanol. Regarding the carbon dioxide conversion and methanol production, the catalysts on which the promoter (zinc) was atomically deposited after copper impregnation (i.e., ZnO/Cu/ZrO2 and ZnO/Cu/ZnO/ZrO2) were superior catalysts compared to the reverse copper-after-zinc catalyst (Cu/ZnO/ZrO2). Temperature-programmed experiments and in situ diffuse reflectance infrared Fourier transform-spectroscopy (DRIFTS) experiments allowed us to elucidate the benefits of the zinc-after-copper pair to store CO2 as carbonate species and further convert them into formate species, key intermediates in the formation of methanol. This research provides insights into the potential of atomic layer deposition in the development of tailored heterogeneous catalysts for efficient CO2 valorization to methanol.Item Film Conformality and Extracted Recombination Probabilities of O Atoms during Plasma-Assisted Atomic Layer Deposition of SiO2, TiO2, Al2O3, and HfO2(AMERICAN CHEMICAL SOCIETY, 2019-11-07) Arts, Karsten; Utriainen, Mikko; Puurunen, Riikka L.; Kessels, Wilhelmus M.M.; Knoops, Harm C.M.; Department of Chemical and Metallurgical Engineering; Catalysis; Eindhoven University of Technology; VTT Technical Research Centre of FinlandSurface recombination of plasma radicals is generally considered to limit film conformality during plasma-assisted atomic layer deposition (ALD). Here, we experimentally studied film penetration into high-aspect-ratio structures and demonstrated that it can give direct information on the recombination probability r of plasma radicals on the growth surface. This is shown for recombination of oxygen (O) atoms on SiO2, TiO2, Al2O3, and HfO2 where a strong material dependence has been observed. Using extended plasma exposures, films of SiO2 and TiO2 penetrated extremely deep up to an aspect ratio (AR) of â900, and similar surface recombination probabilities of r = (6 ± 2) × 10-5 and (7 ± 4) × 10-5 were determined for these processes. Growth of Al2O3 and HfO2 was conformal up to depths corresponding to ARs of â80 and â40, with r estimated at (1-10) × 10-3 and (0.1-10) × 10-2, respectively. Such quantitative insight into surface recombination, as provided by our method, is essential for modeling radical-surface interaction and understanding for which materials and conditions conformal film growth is feasible by plasma-assisted ALD.Item Hydrodeoxygenation and hydrodenitrogenation of n-hexadecanamide over Pt catalysts : effect of the support(Royal Society of Chemistry, 2024-01-21) Verkama, Emma; Albersberger, Sylvia; Arandia, Aitor; Meinander, Kristoffer; Tiitta, Marja; Karinen, Reetta; Puurunen, Riikka L.; Department of Chemical and Metallurgical Engineering; Department of Bioproducts and Biosystems; Catalysis; Neste CorporationEfficient catalysts for simultaneous hydrodeoxygenation (HDO) and hydrodenitrogenation (HDN) are needed for the production of renewable fuels. In this study, Pt catalysts supported on SiO2, γ-Al2O3, SiO2-Al2O3, ZrO2, CeO2-ZrO2, Nb2O5, and TiO2 were studied for the hydrotreatment of n-hexadecanamide (C16 amide) to n-paraffins at 300 °C and 80 bar H2. The catalysts favored HDO over HDN, and the initial differences in the nitrogen removal level were smaller than the differences in the oxygen removal level. The Lewis acid properties of the support influenced the initial C16 amide conversion route and HDO activity, which was reflected in the reaction network and condensation reaction selectivity of the catalysts. Pt/Nb2O5 and Pt/TiO2, with intermediate strength Lewis acid sites, initially favored the HDO of C16 amide to nitrogen-containing compounds. In contrast, the other catalysts converted C16 amide to oxygen- and nitrogen-containing compounds with similar selectivity. The HDO of the oxygen-containing compounds proceeded more efficiently on the Pt catalysts supported on oxides with weak Lewis acid sites (Pt/ZrO2, Pt/CeO2-ZrO2) than on the irreducible oxides with strong or no Lewis acid sites (Pt/γ-Al2O3, Pt/SiO2-Al2O3, Pt/SiO2). As the presence of oxygen-containing compounds suppressed HDN activity, the catalysts with the highest HDO activity eventually gave the highest paraffin yield, regardless of which oxygen removal pathway was favored.Item Hydrodeoxygenation and hydrodenitrogenation of n-hexadecanamide to n-paraffins: Bimetallic catalysts supported on ceria-zirconia(Elsevier Science B.V., 2024-04-25) Verkama, Emma; Järvinen, Ellen; Albersberger, Sylvia; Meinander, Kristoffer; Jiang, Hua; Tiitta, Marja; Karinen, Reetta; Puurunen, Riikka L.; Department of Chemical and Metallurgical Engineering; Department of Bioproducts and Biosystems; Department of Applied Physics; OtaNano; Catalysis; NanoMaterials; Neste CorporationThe development of catalysts for simultaneous hydrodeoxygenation (HDO) and hydrodenitrogenation (HDN) is relevant for the production of renewable fuels. In this work, the activity of CeO2-ZrO2 supported Pt, Co, PtCo, Cu, PtCu, Ni, PtNi, Ru and RuNi catalysts was studied in the hydrotreatment of n-hexadecanamide at 300 °C and 80 bar H2. The bimetallic catalysts differed from the corresponding monometallic catalysts in terms of activity and selectivity. PtCu was less active than the monometallic Pt catalyst, as the addition of Cu suppressed the activity for hydrogenolysis reactions. Pt and PtCo showed a similar activity but a remarkably different selectivity, with Pt favoring n-hexadecane and PtCo favoring n-pentadecane. The RuNi and PtNi catalysts exhibited a higher nitrogen removal and an improved selectivity for n-pentadecane compared to the corresponding monometallic catalysts, emphasizing the potential of catalysts containing Ni and a noble metal. Furthermore, the formation of C32 compounds was limited on RuNi.Item Hydrodeoxygenation Model Compounds γ-Heptalactone and γ-Nonalactone : Density from 293 to 473 K and H2 Solubility from 479 to 582 K(AMERICAN CHEMICAL SOCIETY, 2020-05-14) González Escobedo, José Luis; Uusi-Kyyny, Petri; Puurunen, Riikka L.; Alopaeus, Ville; Department of Chemical and Metallurgical Engineering; Chemical engineeringDetermining the H2 solubility in model compounds that represent lignocellulose derivatives is valuable for the study of upgrading processes such as hydrodeoxygenation. In this work, γ-heptalactone and γ-nonalactone are studied as model compounds at conditions relevant to hydrodeoxygenation. The solubility of H2 in the lactones was determined in the range of 479 to 582 K and 3 to 10 MPa. The solubility measurements were performed in a continuous flow setup based on the visual observation of the bubble point. Furthermore, the densities of the lactones were measured in order to provide the necessary data for the solubility calculations. The density measurements were performed from 293 to 373 K and from 0.16 to 9.9 MPa in a vibrating tube density meter. Using the measurements, a model of the density as a function of temperature and pressure was developed, obtaining average relative deviations on the order of 0.1%. Similarly, the Peng-Robinson equation of state with the Boston-Mathias modification was used to predict the H2 solubility in the lactones. A temperature-dependent model of the symmetric binary parameter of the equation of state was regressed from the data in order to improve the predictions.Item Hydrodeoxygenation of levulinic acid dimers on a zirconia-supported ruthenium catalyst(MDPI AG, 2020-02-01) Mäkelä, Eveliina; Escobedo, José Luis González; Lindblad, Marina; Käldström, Mats; Meriö-Talvio, Heidi; Jiang, Hua; Puurunen, Riikka L.; Karinen, Reetta; School services, CHEM; Catalysis; Neste Corporation; Hydrometallurgy and Corrosion; Department of Applied Physics; Department of Chemical and Metallurgical EngineeringThe hydrodeoxygenation (HDO) of levulinic acid (LA) aldol condensation product dimers was studied between 250 and 300 °C and 50 bar H2 in a batch reactor with Ru catalyst supported on mesoporous zirconia. During the reaction, the unsaturated dimers, which contained ketone groups and double bonds, were hydrogenated to saturated dimers. A greater degree of deoxygenation was achieved at higher temperatures, and oxygen was removed as water and CO2. Oxygen removal was evidenced by elemental analysis and infrared spectroscopy, in which the C=O peak decreased with increasing temperature. A drawback of high reaction temperature (300 °C) was a minor degree of oligomerization. The formation of aromatics was also observed at the higher temperatures. Aside from the saturated dimers, volatile products were obtained at all temperatures, including ketones, acids, and esters. This study demonstrates for the first time the potential of LA dimers as a sustainable route from lignocellulosic biomass to biofuels and biocomponents.Item Hydrodeoxygenation of Propylphenols on a Niobia-Supported Platinum Catalyst : Ortho, Meta, Para Isomerism, Reaction Conditions, and Phase Equilibria(Wiley, 2020-10-01) González Escobedo, José Luis; Mäkelä, Eveliina; Neuvonen, Jouni; Uusi-Kyyny, Petri; Lindblad, Marina; Karinen, Reetta; Puurunen, Riikka L.; Department of Chemical and Metallurgical Engineering; Catalysis; Hydrometallurgy and Corrosion; Organic Chemistry; Chemical engineering; Hydrometallurgy and Corrosion; Neste CorporationThe alkylphenols found in liquefied lignocellulose could become a source of bio-based aromatic hydrocarbons for fuel components. In the hydrodeoxygenation (HDO) of alkylphenols, hydroxyl groups must be removed while avoiding the hydrogenation of the aromatic ring. Here, the HDO of propylphenols is studied using a Pt/Nb2O5 catalyst and n-tetradecane solvent. HDO experiments are performed using different reaction conditions of batch residence time (0–161 min gcat greactant −1), pressure (20–30 bar H2), and temperature (300–375 °C). HDO is studied with ortho-, meta-, and para-propylphenol. The influence of vapor–liquid equilibrium and chemical equilibrium are assessed using thermodynamic calculations. Almost full deoxygenation is attained in the experiments; the main products are propylbenzene and propylcyclohexane. The study finds that, of the isomers, 4-propylphenol is the most favorable for forming propylbenzene (77% maximum selectivity), whereas 2-propylphenol is the least favorable (55% maximum selectivity). Additionally, the reactivity of propylbenzene in the test conditions is detrimental to its selectivity after 5 min gcat greactant −1. Finally, the temperature at which the process favors propylbenzene is found to shift as a function of pressure; at 20 bar, propylbenzene is favored at 350 °C and at 30 bar, it is favored at 375 °C.Item Impact of Ions on Film Conformality and Crystallinity during Plasma-Assisted Atomic Layer Deposition of TiO2(AMERICAN CHEMICAL SOCIETY, 2021-07-13) Arts, Karsten; Thepass, Harvey; Verheijen, Marcel A.; Puurunen, Riikka L.; Kessels, Wilhelmus M.M.; Knoops, Harm C.M.; Department of Chemical and Metallurgical Engineering; Catalysis; Eindhoven University of TechnologyThis work demonstrates that ions have a strong impact on the growth per cycle (GPC) and material properties during plasma-assisted atomic layer deposition (ALD) of TiO2 (titanium dioxide), even under mild plasma conditions with low-energy (<20 eV) ions. Using vertical trench nanostructures and microscopic cavity structures that locally block the flux of ions, it is observed that the impact of (low-energy) ions is an important factor for the TiO2 film conformality. Specifically, it is demonstrated that the GPC in terms of film thickness can increase by 20 to >200% under the influence of ions, which is correlated with an increase in film crystallinity and an associated strong reduction in the wet etch rate (in 30:1 buffered HF). The magnitude of the influence of ions is observed to depend on multiple parameters such as the deposition temperature, plasma exposure time, and ion energy, which may all be used to minimize or exploit this effect. For example, a relatively moderate influence of ions is observed at 200 °C when using short plasma steps and a grounded substrate, providing a low ion-energy dose of ∼1 eV nm-2 cycle-1, while a high effect is obtained when using extended plasma exposures or substrate biasing (∼100 eV nm-2 cycle-1). This work on TiO2 shows that detailed insight into the role of ions during plasma ALD is essential for precisely controlling the film conformality, material properties, and process reproducibility.Item Kinetic modelling of the aqueous-phase reforming of fischer-tropsch water over ceria-zirconia supported nickel-copper catalyst(MDPI AG, 2019-11-01) Coronado, Irene; Arandia, Aitor; Reinikainen, Matti; Karinen, Reetta; Puurunen, Riikka L.; Lehtonen, Juha; Department of Chemical and Metallurgical Engineering; Catalysis; VTT Technical Research Centre of FinlandIn the Fischer–Tropsch (FT) synthesis, a mixture of CO and H2 is converted into hydrocarbons and water with diluted organics. This water fraction with oxygenated hydrocarbons can be processed through aqueous-phase reforming (APR) to produce H2. Therefore, the APR of FT water may decrease the environmental impact of organic waters and improve the efficiency of the FT process. This work aimed at developing a kinetic model for the APR of FT water. APR experiments were conducted with real FT water in a continuous packed-bed reactor at different operating conditions of temperature (210–240◦ C), pressure (3.2–4.5 MPa) and weight hourly space velocity (WHSV) (40–200 h−1) over a nickel-copper catalyst supported on ceria-zirconia. The kinetic model considered C1-C4 alcohols as reactants, H2, CO, CO2 and CH4 as the gaseous products, and acetic acid as the only liquid product. The kinetic model included seven reactions, the reaction rates of which were expressed with power law equations. The kinetic parameters were estimated with variances and confidence intervals that explain the accuracy of the model to estimate the outlet liquid composition resulting from the APR of FT water. The kinetic model developed in this work may facilitate the development of APR to be integrated in a FT synthesis process.Item Liquid-phase Hydrodeoxygenation of 4-Propylphenol to Propylbenzene : Reducible Supports for Pt Catalysts(WILEY-V C H VERLAG GMBH, 2020-08-20) Mäkelä, Eveliina; González Escobedo, José Luis; Neuvonen, Jouni; Lahtinen, Jouko; Lindblad, Marina; Lassi, Ulla; Karinen, Reetta; Puurunen, Riikka L.; School services, CHEM; Department of Chemical and Metallurgical Engineering; Department of Applied Physics; Catalysis; Surface Science; Industrial chemistry; Department of Chemical and Metallurgical Engineering; Neste Corporation; University of OuluPyrolysis and liquefaction biocrudes obtained from lignocellulose are rich in phenolic compounds that can be converted to renewable aromatics. In this study, Pt catalysts on reducible metal oxide supports (Nb2O5, TiO2), along with irreducible ZrO2 as a reference, were investigated in the liquid-phase hydrodeoxygenation (HDO) of 4-propylphenol (350 °C, 20 bar H2, organic solvent). The most active catalyst was Pt/Nb2O5, which led to the molar propylbenzene selectivity of 77 %, and a yield of 75 % (98 % conversion). Reducible metal oxide supports provided an increased activity and selectivity to the aromatic product compared to ZrO2, and the obtained results are among the best reported in liquid-phase. The reusability of the spent catalysts was also studied. The spent Pt/Nb2O5 catalyst provided the lowest conversion, while the product distribution of the spent Pt/ZrO2 catalyst changed towards oxygenates. The results highlight the potential of pyrolysis or liquefaction biocrudes as a source of aromatic chemicals.Item Mechanical and optical properties of as-grown and thermally annealed titanium dioxide from titanium tetrachloride and water by atomic layer deposition(Elsevier Science, 2021-08-31) Ylivaara, Oili M.E.; Langner, Andreas; Liu, Xuwen; Schneider, Dieter; Julin, Jaakko; Arstila, Kai; Sintonen, Sakari; Ali, Saima; Lipsanen, Harri; Sajavaara, Timo; Hannula, Simo-Pekka; Puurunen, Riikka L.; Department of Chemical and Metallurgical Engineering; Department of Electronics and Nanoengineering; Department of Chemistry and Materials Science; Harri Lipsanen Group; Advanced and functional Materials; Catalysis; VTT Technical Research Centre of Finland; Fraunhofer Institute for Material and Beam Technology; University of JyväskyläThe use of thin-films made by atomic layer deposition (ALD) is increasing in the field of optical sensing. ALD TiO2 has been widely characterized for its physical and optical properties, but systematic information about the influence of thermal history to optical and mechanical properties of the film is lacking. Optical applications require planar surface and tunability of the refractive index and residual stress. In addition, mechanical properties such as elastic modulus and film hardness influence the performance of the layer, especially, when optics is integrated with microelectromechanical systems. In this work, optical properties, density, elemental analysis, residual stress, elastic modulus and hardness of as-grown ALD TiO2 thin films on silicon were studied at temperature range from 80 to 350 °C and influence of post-ALD thermal annealing was studied on films annealed up to 900 °C. ALD TiO2 films were under tensile stress in the scale of hundreds of MPa. The stress depended both on the ALD temperature and film thickness in a complex way, and onset of crystallization increased the residual stress. Films grown at 110 and 300 °C were able to withstand post-ALD annealing at 420 °C without major change in residual stress, refractive index or extinction coefficient. Elastic modulus and hardness increased upon crystallization with increasing ALD temperature. The results presented here help to improve the design of the optical devices by choosing films with desired optical properties, and further help to design the post-ALD thermal budget so that films maintain their desired features.Item Microscratch testing method for systematic evaluation of the adhesion of atomic layer deposited thin films on silicon(2016-01-01) Kilpi, Lauri; Ylivaara, Oili M. E.; Vaajoki, Antti; Malm, Jari; Sintonen, Sakari; Tuominen, Marko; Puurunen, Riikka L.; Ronkainen, Helena; Department of Micro and Nanosciences; Department of Chemical and Metallurgical Engineering; VTT Technical Research Centre of Finland; University of Jyväskylä; ASM Microchemistry OyThe scratch test method is widely used for adhesion evaluation of thin films and coatings. Usual critical load criteria designed for scratch testing of coatings were not applicable to thin atomic layer deposition (ALD) films on silicon wafers. Thus, the bases for critical load evaluation were established and the critical loads suitable for ALD coating adhesion evaluation on silicon wafers were determined in this paper as LCSi1, LCSi2, LCALD1, and LCALD2, representing the failure points of the silicon substrate and the coating delamination points of the ALD coating. The adhesion performance of the ALD Al2O3, TiO2, TiN, and TaCN+Ru coatings with a thickness range between 20 and 600 nm and deposition temperature between 30 and 410°C on silicon wafers was investigated. In addition, the impact of the annealing process after deposition on adhesion was evaluated for selected cases. The tests carried out using scratch and Scotch tape test showed that the coating deposition and annealing temperature, thickness of the coating, and surface pretreatments of the Si wafer had an impact on the adhesion performance of the ALD coatings on the silicon wafer. There was also an improved load carrying capacity due to Al2O3, the magnitude of which depended on the coating thickness and the deposition temperature. The tape tests were carried out for selected coatings as a comparison. The results show that the scratch test is a useful and applicable tool for adhesion evaluation of ALD coatings, even when carried out for thin (20 nm thick) coatings.Item Modeling growth kinetics of thin films made by atomic layer deposition in lateral high-aspect-ratio structures(2018-05-28) Ylilammi, Markku; Ylivaara, Oili M.E.; Puurunen, Riikka L.; Department of Chemical and Metallurgical Engineering; Catalysis; VTT Technical Research Centre of FinlandThe conformality of thin films grown by atomic layer deposition (ALD) is studied using all-silicon test structures with long narrow lateral channels. A diffusion model, developed in this work, is used for studying the propagation of ALD growth in narrow channels. The diffusion model takes into account the gas transportation at low pressures, the dynamic Langmuir adsorption model for the film growth and the effect of channel narrowing due to film growth. The film growth is calculated by solving the diffusion equation with surface reactions. An efficient analytic approximate solution of the diffusion equation is developed for fitting the model to the measured thickness profile. The fitting gives the equilibrium constant of adsorption and the sticking coefficient. This model and Gordon's plug flow model are compared. The simulations predict the experimental measurement results quite well for Al2O3 and TiO2 ALD processes.
