Aaltodoc Repository :: Browsing by Author "Puurunen, Riikka"

Browsing by Author "Puurunen, Riikka"

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Acidity characterisation of zeolites for glycerol aromatisation with temperature-programmed desorption
(2024-01-23) Järvinen, Ellen; Karinen, Reetta; Velasco, Jorge; Kemian tekniikan korkeakoulu; Puurunen, Riikka
Zeolites are among the most industrially significant solid acid catalysts. Effective and accessible methods for analysing the acidity of solid materials are critical for zeolite-related catalyst research, as the acidity characterisation elucidates the relationship between the properties and the catalytic activity of the material. The temperature-programmed desorption (TPD) of basic probe molecules is a widely reported method for characterising the acidity of solids. Automated TPD instruments requiring little operator input are available commercially, which makes the method particularly accessible for routine acidity characterisation. Typical probe molecules used in the analysis of zeolites with TPD include ammonia (NH3) and isopropylamine (IPAm). This work implemented a NH3-TPD and an IPAm-TPD method for determining the total acidity and the Brønsted acidity of zeolitic samples respectively. This work also compared NH3-TPD and IPAm-TPD as acidity characterisation methods for zeolites. The theory part of this work covered the principles of zeolite catalysts and TPD and examined previously reported NH3-TPD and IPAm-TPD methods. In the experimental part, a NH3-TPD and an IPAm-TPD method were developed, and sample materials intended for glycerol aromatisation were characterised with the developed NH3-TPD and IPAm-TPD methods. The NH3-TPD and IPAm-TPD methods developed in this work produced TPD profiles that corresponded well to descriptions of zeolite NH3-TPD and IPAm-TPD profiles available in literature. Out of the tested materials, only the Zn-modified zeolite sample produced an abnormal IPAm-TPD profile. The total acidity and Brønsted acidity results calculated from the TPD data were logical with respect to the theoretical acidity of the studied materials. As an exception, the IPAm-TPD analysis of the γ-Al2O3 reference sample yielded a higher value for Brønsted acidity than expected. This was suspected to be due to Brønsted acid sites associated with impurities. The relative standard deviation of both the total and Brønsted acidity results was 4% in the repeat tests.
Aluminum oxide/titanium dioxide nanolaminates grown by atomic layer deposition: Growth and mechanical properties
(2017-01-01) Ylivaara, Oili M E; Kilpi, Lauri; Liu, Xuwen; Sintonen, Sakari; Ali, Saima; Laitinen, Mikko; Julin, Jaakko; Haimi, Eero; Sajavaara, Timo; Lipsanen, Harri; Hannula, Simo-Pekka; Ronkainen, Helena; Puurunen, Riikka; Department of Chemistry and Materials Science; Department of Materials Science and Engineering; Department of Micro and Nanosciences; Department of Chemical and Metallurgical Engineering; Department of Electronics and Nanoengineering; Harri Lipsanen Group; VTT Technical Research Centre of Finland; University of Jyväskylä; Department of Materials Science and Engineering
Atomic layer deposition (ALD) is based on self-limiting surface reactions. This and cyclic process enable the growth of conformal thin films with precise thickness control and sharp interfaces. A multilayered thin film, which is nanolaminate, can be grown using ALD with tuneable electrical and optical properties to be exploited, for example, in the microelectromechanical systems. In this work, the tunability of the residual stress, adhesion, and mechanical properties of the ALD nanolaminates composed of aluminum oxide (Al2O3) and titanium dioxide (TiO2) films on silicon were explored as a function of growth temperature (110-300 °C), film thickness (20-300 nm), bilayer thickness (0.1-100 nm), and TiO2 content (0%-100%). Al2O3 was grown from Me3Al and H2O, and TiO2 from TiCl4 and H2O. According to wafer curvature measurements, Al2O3/TiO2 nanolaminates were under tensile stress; bilayer thickness and growth temperature were the major parameters affecting the stress; the residual stress decreased with increasing bilayer thickness and ALD temperature. Hardness increased with increasing ALD temperature and decreased with increasing TiO2 fraction. Contact modulus remained approximately stable. The adhesion of the nanolaminate film was good on silicon.
Atomic layer deposited platinum in porous spheres and on well-defined high-aspect-ratio structures: Experiments and modelling
(2023-01-24) Järvilehto, Jänis; Saedy, Saeed; Gonsalves, Christine; Kemian tekniikan korkeakoulu; Puurunen, Riikka
Atomic layer deposition (ALD) has in recent years seen increasing interest for the synthesis of supported metal catalysts, due to the high level of control the method provides over the particle properties, as well as its ability to coat narrow structures, such as pores. To study ALD in narrow structures, specialized high-aspect-ratio (HAR) test structures have been developed. In this work, ALD was used to deposit platinum on porous alumina (Al2O3) spheres and well-defined, lateral high-aspect-ratio (LHAR) structures. The work included a literature review, where the ALD process, ALD reactors, ALD in HAR structures, as well as the ALD of platinum are briefly introduced. ALD was performed using (trimethyl)methylcyclopentadienylplatinum(IV) (MeCpPtMe3) and synthetic air. The alumina spheres were processed in a fluidized bed reactor, while the LHAR structures were mounted in the windbox of the setup. The MeCpPtMe3 exposure duration was varied throughout the series. The samples were characterized using inductively coupled plasma - optical emission spectrometry, X-ray photoelectron spectroscopy and low-energy ion scattering. Saturation profiles obtained from the samples’ inner surfaces were compared with each other, as well as with the outcome of a diffusion-reaction model. The results showed that platinum was deposited in all cases. A clear trend of increasing penetration depth with longer MeCpPtMe3 exposure durations was observed in the alumina spheres. The simulations predicted diffusion of the metal precursor throughout the LHAR structures with the longest exposure durations - a result compatible with the experimentally observed growth. This work presents initial research comparing ALD in porous particles and LHAR structures and provides a starting point for the optimization of the diffusion-reaction model parameters for the deposition of platinum in said materials.
Atomic layer deposition coatings in catalytic high-temperature filtration of gasification gas
(2019-07-31) Viertiö, Tyko; Kivelä, Viivi; Kemian tekniikan korkeakoulu; Puurunen, Riikka
The aim of the thesis was to develop a method for preparation of catalytic filters for gasification gas cleaning by atomic layer deposition (ALD). In the literature part, catalysts for tar decomposition, the factors in filter and membrane coatings affecting the reactivity in catalytic filtration and atomic layer deposition prepared nickel and rhodium catalysts were reviewed. Main challenge of the gasification gas cleaning catalysts is maintaining high activity despite the deactivation due to sulphur poisoning and coke formation. Nickel and rhodium catalysts supported on Al2O3 were found to be the most promising catalyst options for further development. Challenge of the preparation of catalytic filters is the low surface area, which limits the amount and consequently the active surface area of the catalyst deposited on the filter. ALD is an interesting option for catalyst preparation, since it provides method for preparation of stabile and high active metal surface area catalysts. In the experimental part, set of catalytic filters was prepared by atomic layer deposition of Al2O3 support layer and nickel or rhodium layers as active metals on steel filter discs. Catalytic filters were characterized with SEM-EDS and tested for catalytic filtration of model gasification gas in lab scale reactor at temperatures ranging from 650 to 920 °C and at pressure of 5 bar. Nickel catalysts were prepared with top surface nickel loading ranging from 1 to 14 w-% but no deposition on inner surfaces of the filter was achieved. Due to low overall amount of nickel, no significant catalytic activity was observed in reaction tests. The highest catalytic activity was achieved with nickel-containing steel alloy 316L filter at 920 °C. No sufficient deposition of rhodium on filters was achieved and major process development of parameters of ALD in current reactor setup is needed for reliable rhodium catalyst preparation.
Atomic layer deposition of niobium nitride thin films
(2014-12-02) Rontu, Ville; Puurunen, Riikka; Kemian tekniikan korkeakoulu; Franssila, Sami
Niobium nitride thin films have been usually deposited by reactive magnetron sputtering. Atomic layer deposition (ALD) has emerged as viable candidate for growth of ultrathin films. Its benefits include conformal deposition and nanometer scale thickness control. So far deposition of cubic NbN phase has been realized by ALD from NbCl5 and NH3 only with help of zinc as an additional reducing agent or by PEALD from organometallic precursors. In this work we developed deposition processes for recently acquired ALD tool aiming for deposition of NbN from NbCl5 without zinc. We deposited NbNx thin films from NbCl5 using NH3, H2 and NH3 as separate pulses; NH3-plasma; H2/N2-plasma with varying flow rate ratios; and H2-plasma. PEALD depositions in this work are the first published PEALD processes for NbN using NbCl5 as a precursor. Thermally deposited films using NH3 had resistivity of 650 μΩcm at best and growth rate varied from 0.34–0.52 Å/cycle. Resistivity is slightly higher than the best, 550–600 μΩcm, reported for similar process. Also GPC is higher than typically reported 0.25 Å/cycle. Films were clean having less than 1 at% impurities for films grown at 500°C. Cl-content increased from 0.3 at% to 1.8 at% as deposition temperature decreased from 500°C to 400°C. Nb/N ratios in the films were close to 0.8. Films grown with plasma typically exhibited even higher GPC, 0.5–0.85 Å/cycle. Exception to this was film grown on top of amorphous AlN which had growth rate of 0.35 Å/cycle. The best resistivity obtained for plasma processes was 490 μΩcm. ToF-ERDA measurements from H2-plasma grown film revealed incorporation of nitrogen into the film from carrier gas lines. None of the grown films exhibited superconductivity. It was determined that NH3 has insufficient reducing power to create stoichiometric NbN and that use of H2 to replace zinc as additional reducing agent would require higher temperatures. Deposition of superconductive NbN films should be possible with plasma-enhancement after changes to the ALD equipment is made in order to fully operate under argon atmosphere.
Atomikerroskasvatus katalyyttien valmistustekniikkana
(2017-12-04) Rönkä, Rasmus; Puurunen, Riikka; Kemiantekniikan korkeakoulu; Rautkari, Lauri
Catalytic aqueous phase reforming of the Fischer-Tropsch derived water fraction: Kinetics and reactor modeling
(2019-01-29) Ali, Jama; Coronado, Irene; Lehtonen, Juha; Kemian tekniikan korkeakoulu; Puurunen, Riikka
Dilute organic wastewater such as Fischer-Tropsch (FT) derived water is generated in large amounts during the liquefaction process of synthesis gases (H2+CO) into fuels. The FT derived water contains a small number of organic compounds, as a result, purification treatment is required. However, current treatment methods are expensive and complex. Therefore, there is a need for innovative alternative treatment methods for these waste streams, which would increase overall process efficiency of FT synthesis. Aqueous phase reforming (APR) is a promising treatment method for dilute organic wastewater. APR purifies and upgrades the organic content in the water into valuable chemicals, such as hydrogen. The research done so far on APR method has mainly used a single model feedstock compound among short and long chain alcohols to describe overall APR reactions of the FT wastewater. Furthermore, previous studies focused mainly on catalyst development, therefore the APR method is still in the development phase. More studies relating to APR reaction kinetics with phase interactions and reactor modeling with more realistic feedstock is required for the future commercial application of APR method. The aim of this study was to investigate the APR of FT derived water by assessing and developing a kinetic model with pseudo-homogenous assumptions. Due to this approach, external and internal mass transfer were neglected in the model and only the molecular diffusion of feedstock components and products in liquid-gas interphases were examined. The kinetic model was based on simultaneous APR reactions of real FT derived water fractions: methanol, ethanol, propanol, and butanol into H2 and CO2 via water-gas shift (WGS) reaction. In addition to this, several reactor models were assessed, in order to find the most suitable reactor for the study of the APR method. Peng-Robinson thermodynamic property model was used to predict the liquid-gas system compositions in reactor concept simulation of APR since the model was designed for high-pressure systems, such as in this study and it predicted the liquid density more accurately than SRK model, which is also a commonly used method in liquid-gas simulation studies. The alcohol feedstock composition used in the development of the kinetic model represented well APR and WGS of real FT derived water fractions into gaseous products because alcohols made 2.65 % out of total 3.5 % of the organic content and mainly alcohols, such as methanol contributed most to gaseous product generation. The results relating to the absence of external and internal mass transfer limitations estimated with Weisz-Pratern (CWp) and Mears (MR) criterion supported the application of pseudo-homogeneous assumptions. Adoption of the power law as a rate law was more practical in establishing the kinetic model into an applicable mathematical format, rather than using Langmuir-Hinshelwood-Hougen-Watson (LHHW) model. The kinetic model prediction of H2 and CO2 generation did not represent well the experimental results, therefore the model requires further development relating to equilibrium constant estimation. The simulation results of reactors relating to gaseous products, phase distribution and conversion predictions, the plug flow model were most suitable reactor model for APR studies compared to stoichiometric and equilibrium models.
Catalytic dehydrogenation of liquid organic hydrogen carriers
(2018-11-06) Braunschweiler, Aki; Kaisalo, Noora; Kemian tekniikan korkeakoulu; Puurunen, Riikka
Liquid organic hydrogen carriers (LOHCs) provide a novel method for storing hydrogen. Hydrogen is chemically bound to a carrier compound, which means that hydrogen is not in its flammable form and in addition, no boil-off occurs. Because of this, storage in LOHCs is safer and more efficient, compared to conventional storage methods. The main focus of the literature part is in presenting and comparing different reactor concepts for LOHC research and commercial applications. It was found, that micro-structured reactors or heat exchanger reactors could be the most optimal reactor concepts for LOHC dehydrogenation applications as they offer the best heat and mass transfer of all studied reactor concepts. Currently, only one commercial LOHC unit exists. The most commonly used and most researched LOHC compounds are dibenzyltoluene, N-ethyl-carbazole and methylcyclohexane. The environmental hazards of LOHC compounds are related to their decomposition products, e.g. benzene. The experimental part of this thesis covers the dehydrogenation of perhydro-dibenzyltoluene on different platinum catalysts. The tested catalysts were Pt/Al2O3 in packed bed and washcoat form, Pt/TiO2 in washcoat form and Pt/C in packed bed form. The experiments were carried out on different temperatures (270 - 300 °C) and space velocities to compare how the catalysts perform at different conditions. In addition, longer, 48h experiments were carried out to observe catalyst behavior during longer continuous operation. In general, the degree of dehydrogenation (conversion) was higher at lower space velocities (longer residence time) and higher temperatures. The degree of decomposition was observed to be proportional to the degree of dehydrogenation. Washcoat catalysts generally yielded lower degree of decomposition than packed bed catalysts. Of the studied catalysts, Pt/TiO2 was found to be the best dehydrogenation catalyst as it yielded the highest degree of dehydrogenation and lowest degree of decomposition at typical dehydrogenation conditions. At 300 °C with weight hourly space velocity of 4.57 h-1 the degree of dehydrogenation was 39 % and degree of decomposition was 0.7 %. Based on the experimental results and the literature review, a micro-structured reactor or a heat exchanger reactor with multiple narrow tubes washcoated with Pt/TiO2 would be a viable rector concept for commercial LOHC dehydrogenation applications.
Catalytic systems in the purification of carbon monoxide from hydrogen and ethylene-rich gasses
(2023-10-10) Vartiainen, Aleksi; Nikkanen, Ville; Kemian tekniikan korkeakoulu; Puurunen, Riikka
Thermochemical methods such as pyrolysis and gasification can be used in the chemical recycling of unsorted, plastic waste. The gas fraction that is produced contains carbon monoxide, carbon dioxide, hydrogen, methane and light olefins. Before the light olefins can be re-polymerized to produce new plastics, the gas stream must be purified of all impurities, including CO. CO removal from gas streams is an important industrial process. Catalytic methods for CO removal include water-gas shift (WGS), methanation and CO oxidation. However, there is limited research on the use of these methods for the purification of CO from hydrogen and ethylene-rich gasses. This thesis screened the CO purification performance of a selection of eight commercial and research stage catalysts that have been developed for WGS, methanation and CO oxidation reactions. WGS catalysts included two Fe2O3/Cr2O3 high-temperature shift (HTS) catalysts, two CuO/ZnO/Al2O3 low-temperature shift (LTS) catalysts and one ZrO2 based catalyst. Methanation catalysts included one NiO catalyst and one CoMo catalyst. CO oxidation catalysts included one CuO/ZnO catalyst. The catalytic performance was evaluated on the basis of CO removal and level of C2H4 that remains in the gas. The CO and C2H4 removal of the selected catalysts was experimentally tested in a bench-scale atmospheric plug-flow reactor. The gas stream to be purified was simulated using a mixture of CO, CO2, H2, CH4, C2H4 and N2. A simulation of the reactor was made to further understand the thermodynamical equilibrium of the reactions and to evaluate the experimental CO conversion against the equilibrium conversion. The best overall performance was achieved with HTS Fe2O3/Cr2O3 catalysts, achieving 70-80 percentage CO conversion and less than 5 percentage ethylene conversion. Comparatively, the LTS CuO/ZnO/Al2O3 catalysts convert CO at over 97 percentage and ethylene at over 99 percentage conversion.
Characterization and testing of zinc copper-based catalysts supported on different metal oxides for carbon dioxide hydrogenation to methanol
(2022-08-23) Sajid, Ahmed; Arandia, Aitor; Yim, Jihong; Kemian tekniikan korkeakoulu; Puurunen, Riikka
Carbon dioxide emissions are one of the major causes of global climate change. In this regard, carbon dioxide conversion to methanol can serve as one of the promising solutions to mitigate climate change problems. This thesis aimed to screen different metal oxide supports such as ZrO2, 17%CeO2-ZrO2, 25%CeO2-ZrO2, 17%CeO2-5La2O3-ZrO2, Al2O3, Nb2O5 and TiO2 for their role in promoting the activity and selectivity of ZnCu-based catalyst for methanol synthesis from direct hydrogenation of carbon dioxide. The role of zinc oxide as a promoter on metal oxide supported copper catalyst was also explored. Recent progress in the development of metal oxide-supported zinc copper-based catalysts was presented and discussed in the literature review. In the experimental part of the thesis, characterization of catalysts was performed by hydrogen temperature programmed reduction and scanning transmission electron microscopy. The catalytic activity was measured in the continuous flow fixed bed reactor. Among different metal-oxide supported catalysts, ZrO2-supported ZnCu catalyst showed the highest methanol space time yield while TiO2-supported catalysts showed least methanol space time yield. The deposition of ZnO by atomic layer deposition on metal oxide supported copper catalysts showed positive influence on activity and selectivity of the catalysts. Based on the results of this thesis, zirconia support was the most promising among others for increasing activity and selectivity of the ZnCu-based catalyst. Further experiments are recommended to establish structure-activity relationship for ZnCu-based catalysts for their role towards CO2 hydrogenation.
Conversion of furfural to 2-methylfuran over CuNi catalysts supported on biobased carbon foams
(ELSEVIER SCIENCE BV, 2021-05-01) Varila, Toni; Mäkelä, Eveliina; Kupila, Riikka; Romar, Henrik; Hu, Tao; Karinen, Reetta; Puurunen, Riikka; Lassi, Ulla; School services, CHEM; Department of Chemical and Metallurgical Engineering; Catalysis; University of Oulu
In this study, carbon foams prepared from the by-products of the Finnish forest industry, such as tannic acid and pine bark extracts, were examined as supports for 5/5% Cu/Ni catalysts in the hydrotreatment of furfural to 2-methylfuran (MF). Experiments were conducted in a batch reactor at 503 K and 40 bar H2. Prior to metal impregnation, the carbon foam from tannic acid was activated with steam (S1), and the carbon foam from pine bark extracts was activated with ZnCl2 (S2) and washed with acids (HNO3 or H2SO4). For comparison, a spruce-based activated carbon (AC) catalyst and two commercial AC catalysts as references were investigated. Compressive strength of the foam S2 was 30 times greater than that of S1. The highest MF selectivity of the foam-supported catalysts was 48 % (S2, washed with HNO3) at a conversion of 91 %. According to the results, carbon foams prepared from pine bark extracts can be applied as catalyst supports.
Cyclic adsorption studies on carbon dioxide hydrogenation to methanol using diffuse reflectance infrared Fourier transform spectroscopy and mass spectrometry
(2021-06-15) Warraich, Hassaan; Arandia Gutierrez, Aitor; Kemian tekniikan korkeakoulu; Puurunen, Riikka
The transformation of carbon dioxide into useful product i.e., methanol using tailor-made catalysts is a crucial step towards reduction of carbon dioxide concentration in atmosphere. Studying the interaction between the gases (CO2 and H2) and the catalyst surface is of great significance as it helps to understand the reaction intermediates and pathways. As Cu and Zn metals, reportedly, are active towards CO2 hydrogenation to methanol, this work studied the cyclic adsorption of CO2 and H2 to understand the behaviour of Cu and Zn over zirconia samples towards adsorption of the fed gases. The formation of expected intermediate species i.e., carbonates, bicarbonates, formates, methoxy and methanol, over samples and the products formed were analysed using in-situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) and mass spectrometry (MS), respectively. The literature review discusses the concept of methanol economy and development of heterogeneous catalyst for CO2 to methanol conversion. Focus of study was given to the characterization of the catalytic materials used in CO2 to methanol reaction. The probe molecules i.e., CO2 and H2, and intermediate species and products, formed during the reaction were described in relation to the absorption bands displayed in DRIFTS. The experimental part of thesis initiated by obtaining the prepared zirconia-based samples i.e., ZrO2, Cu/ZrO2, Zn/ZrO2 and Cu/Zn/ZrO2, using incipient wetness impregnation for Cu impregnation and atomic layer deposition for Zn over zirconia. The cyclic adsorption tests consisted of three cycles of CO2 and H2 flow with Ar purge in between each gas flow at 450, 500 and 550 K, conditions that were defined after initial pre-study experiments. The results displayed that monodentate carbonates and bidentate bicarbonates were formed on all zirconia samples while formates were only observed with H2 flow in presence of Cu or Zn over zirconia. The formates had strong adsorption over the sample surface and seemed to form from monodentate carbonates. While bicarbonates were weakly adsorbed, these disappeared with inert gas purge and were not related to formate appearance. Among the samples, Zn/ZrO2 displayed promising results with a good ability to retain carbonates on the surface during CO2 flow and convert them to formates during H2 flow.
Development of a powder atomic layer deposition reactor for research purposes
(2022-10-10) Andsten, Simon; Puurunen, Riikka; Larkiala, Sauli; Insinööritieteiden korkeakoulu; Ekman, Kalevi
Atomic layer deposition (ALD) is process that creates thin layers of solid material by using gas-phase chemicals. The ALD process is used in the industry for semiconductor manufacturing. Commercial systems have been developed to achieve an ALD process that suits the industry requirements. In contrast, custom ALD systems are developed for research purposes with a smaller budget. Consequently, the aim of this thesis is to develop a reactor assembly to increase the number of ALD systems at Aalto University, School of Chemical Engineering, to aid research. The development of a new custom system also gave the opportunity to implement additional measurement systems and increase the operating temperature. The conducted design process in this thesis included a brief design comparison of two reactor types, a short presentation of the ALD system, the design challenges and decision made on the reactor assembly, manufacturing and assembly, and a proposed test for examining the safety and performance of the reactor assembly. The completed ALD reactor assembly was able to implement most of the desired equipment, which consisted mainly of a multipoint thermocouple inside the reactor tube, and the capability to operate in both vacuum and atmospheric pressure. The exceptions were a quartz crystal microbalance sensor and an infra-red thermal camera, which could not be added due to size and cost restrictions. In the reactor assembly prototype, the furnace has a temperature capability of 800°C. The furnace also supports the detachable reactor tube with ability to transfer samples in inert gas. The reactor tube seals and connections were designed accordingly to accommodate the temperatures up to 800°C, that the reactor furnace can reach. Cooling channels were added to protect the o-ring seals between the reactor tube flanges and metals flanges that connect the reactor tube to the rest of the piping system. The parts were then manufactured and assembled as far as possible with the parts at hand.
Development of hafnium and aluminum oxide processes in a new laminar flow atomic layer deposition reactor
(2021-05-18) Näsi, Mikko; Blomberg, Tom; Kemian tekniikan korkeakoulu; Puurunen, Riikka
Effect of water and atomic layer deposited overcoating on cobalt-based Fischer-Tropsch catalyst
(2020-10-20) Palo, Jasmiina; Heikkinen, Niko; Kemian tekniikan korkeakoulu; Puurunen, Riikka
This master’s thesis studies the effect water and atomic layer deposited (ALD) overcoating on activity, selectivity, and stability of cobalt catalyst in Fischer-Tropsch (FT) synthesis. ALD is a thin-film deposition technique based on sequential, self-limiting gas-solid reactions, and can be used to design and synthesize heterogeneous catalysts. ALD can also be used to grow protective films over porous catalysts. These ALD overcoatings are found to enhance catalytic activity and selectivity, and can improve catalyst stability against deactivation in high-temperature processes and liquid-phase reactions. The literature part of the thesis presents different catalyst overcoating techniques and their successful examples, with an emphasis on ALD overcoatings. The principle of both ALD technique and FT synthesis are also presented. In addition, the effect of water on cobalt-based catalysts in FT synthesis is reviewed. In the experimental part, the effect of water and ALD overcoating on the performance of cobalt-based FT catalyst was studied. A Co-Pt-Si/γ-Al2O3 catalyst was synthesized by co-impregnation technique and was further overcoated with 0, 30, 35, and 40 cycles of alumina ALD. The reaction experiments were conducted in a fixed-bed reactor at 20 bar, 200 °C, and with H2/CO molar ratio of 2.0. The effect of water was tested by increasing the feed water concentration in a step-wise manner. Furthermore, one experiment without water addition was carried out with the non-ALD-overcoated catalyst and with the catalyst with 40 cycles of ALD to study the effect of overcoating in a long-term. The catalyst with 40 cycles of alumina was found to be more active and stable compared to the other catalysts. In the experiment without added water, the catalyst with 40 cycles of ALD maintained stable activity during 144 h on stream. In addition, the same catalyst showed improved stability at low water concentrations (20 mol-%) with only 2 % loss of catalytic activity, while other catalyst lost 19-27 % of their activity at similar conditions. At high water concentrations (30 mol-%), all catalysts suffered from permanent deactivation, and only a relatively small part of the catalysts’ activities were recovered after the water supply was turned off. All catalysts showed decreased methane selectivity and increased long-chain hydrocarbon selectivity upon water additions. ALD overcoating was found to enhance secondary hydrogenation of olefins, which was seen as decreased olefin-to-paraffin ratio. Moreover, the overcoating increased methane selectivity and decreased formation of long-chain hydrocarbons.
Evidence for low-energy ions influencing plasma-assisted atomic layer deposition of SiO2: Impact on the growth per cycle and wet etch rate
(AMER INST PHYSICS, 2020-07-22) Arts, Karsten; Deijkers, J. H.; Faraz, T.; Puurunen, Riikka; Kessels, Wilhelmus M.M. (Erwin); Knoops, Harm C. M.; Department of Chemical and Metallurgical Engineering; Catalysis; Eindhoven University of Technology
This work provides evidence that plasma-assisted atomic layer deposition (ALD) of SiO2, a widely applied process and a cornerstone in self-aligned multiple patterning, is strongly influenced by ions even under mild plasma conditions with low-energy ions. In two complementary experimental approaches, the plasma ALD of SiO2 is investigated with and without the contribution of ions. The first set of experiments is based on microscopic cavity structures, where part of the growth surface is shielded from ions by a suspended membrane. It is observed that a lower growth per cycle (GPC) and a better material quality are obtained when an ion contribution is present. Without any ion contribution, a GPC of 1.45 ± 0.15 Å/cycle and a wet etch rate of 4 ± 1 nm/s (in 30:1 buffered HF) are obtained for a deposition temperature of 200 °C. With an ion contribution, these values decrease, where the magnitude of the decrease appears to be determined by the supplied ion energy dose. For extended ion doses, the GPC decreases to 0.85 ± 0.05 Å/cycle and the wet etch rate to 0.44 ± 0.09 nm/s, approaching the value for a thermal oxide. The important role of ions is confirmed by the second experimental approach, which is based on ion-selective quartz crystal microbalance measurements. By these results, it is demonstrated that ions have a stronger impact on the plasma ALD of SiO2 than usually considered, providing essential insights for tailoring the film growth.
Fracture properties of atomic layer deposited aluminum oxide free-standing membranes
(2015) Berdova, Maria; Ylivaara, Oili M. E.; Rontu, Ville; Törmä, Pekka T.; Puurunen, Riikka; Franssila, Sami; Department of Materials Science and Engineering; Department of Micro and Nanosciences; Department of Chemistry and Materials Science; Department of Chemical and Metallurgical Engineering
Gold catalyst supported on titania for 1-butanol partial oxidation in a microreactor
(2019-03-12) Tiitinen, Janne; Khan, Yaseen; Viinikainen, Tiia; Kemian tekniikan korkeakoulu; Puurunen, Riikka
Theoretical background of the catalytical activity of gold nanoparticles, TiO2 as support, sol-immobilization method and oxidation of alcohols in microreactor are explained briefly in the literature part. In the experimental part, five gold on titania (TiO2) support catalysts were made with sol-immobilization method. Catalyst were made to observe the effect of catalyst preparation parameters to the size of gold particles, size distribution of the gold particles and the activity of the catalyst. Preparation parameters were the amount of gold in the solution, the pH adjustment timing and the pH level of the catalyst preparation solution. As catalytic activity test reaction 1-butanol was partial oxidized to butyraldehyde. The catalysts were prepared with target loading of 0.3, 0.6 and 1.0 wt.% Au/TiO2. The effect of adding H2SO4 at different stages of catalyst preparation was tested by acidifying the gold nanoparticle solution before addition of the support instead of acidifying after addition of the support. The wanted target acidity of the solution varied from pH 1 to 3. Catalysts were characterized by transmission electron microscopy (TEM), energy dispersive spectroscopy, x-ray fluorescence, thermogravimetric analysis, x-ray photoelectron spectroscopy and rheology, and tested in a microreactor for 1-butanol partial oxidation in the gas phase. All the catalysts were tested at temperature range of 130 to 400 °C and partial pressure of 13.5 kPa. One catalyst was tested also at 1-butanol partial pressure of 18.0 kPa. The TEM analysis showed that the 1.0 wt.% Au/TiO2 sample gave 3.9 nm average size of Au particles and 0.3 wt.% sample 2.0 nm average size of particles. Acidifying the catalyst preparation solution before adding TiO2 affected size of the particles by reducing their average size from 3.9 to 3.2 nm. Acidifying the catalyst preparation solution to pH 3 instead of 1, increased the average size of the particles from 2.7 to 3.8 nm with 0.6 wt.% Au/TiO2 sample. All catalysts yielded 20% - 55% of butyraldehyde at 400 °C. Yields of other products such as carbon monoxide (3% - 10%), carbon dioxide (5% - 25%), trans-2-butene (1% - 10%), 1-butene (1% - 5%) and propene (0% - 5%) at 400 °C were observed. By decreasing the residence time and increasing the partial pressure of 1-butanol it was possible to have more selective reactor conditions to butyraldehyde.
Heterogeneously catalysed light olefin epoxidation with hydrogen peroxide
(2022-10-18) Kuutti, Krista; Rautiainen, Sari; Lehtonen, Juha; Kemian tekniikan korkeakoulu; Puurunen, Riikka
This thesis studied the performance of heterogeneous titanium silicate catalysts in ethene and propene epoxidation by hydrogen peroxide. The catalyst performance was evaluated in terms of alkene conversion and product selectivity. The work aim was to find potential heterogeneous catalysts for combined light olefin epoxidation. However, the olefins were experimented with in separate experiments to discover their differences in the epoxidation process. The literature part investigated heterogeneous catalysts for liquid-phase light olefin epoxidation. The main content is a review of heterogeneous catalysts that could possibly operate in a continuous hydrogen-peroxide-oxidized epoxidation of light alkenes. In addition, the modern industrial C2–C4 olefin epoxidation processes were presented to provide context of the commercial process requirements. In the experimental part, hydrogen-peroxide-oxidized epoxidation of ethene and propene over titanium silicate catalysts was studied. The experiments were conducted in mild conditions (max. 4.5 barg pressure and 45°C temperature) in a continuously operated laboratory sized trickle-bed reactor. The oxidant was fed as a solution that contained 2 wt.-% H2O2 in methanol. Ethene epoxidation was studied over a commercial titanium silicate-1 (TS-1) molecular sieve catalyst, and propene epoxidation both over the commercial catalyst and its modified version. The catalyst modification was a hydrothermal treatment with tetrapropylammonium hydroxide (TPAOH), and the modification aim was to create a hierarchical porous structure to the TS-1 catalyst. During the experiments, the modified TS-1 catalyst provided a higher propylene oxide (PO) selectivity (60–77%) than the un-modified TS-1 catalyst (55–60%). However, even the best achieved PO selectivity over the modified catalyst was low (77%) compared to the literature, where TS-1 catalyst has been commonly reported to provide near complete PO selectivity in corresponding processes. The cause for low PO selectivity was likely an excess of the H2O2 oxidant. In ethene epoxidation experiments, ethene was converting to epoxide ring opening by-products, but no ethylene oxide could be detected. Overall, both ethene and propene epoxidation results relied strongly on the process conditions. In optimum conditions the TS-1 catalyst or its modified version could possibly provide commercially viable epoxidation processes for both alkenes.
Lähtöaineet nikkelimateriaalien atomikerroskasvatusprosesseissa
(2022-05-08) Tuomi, Taru; Puurunen, Riikka; Kemiantekniikan korkeakoulu; Kontturi, Eero

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