On the Function of Ceria Supported Rhodium Catalysts for Methanation of Carbon Dioxide

Technologies for energy harvesting of sustainable sources such as solar and wind lack an inherent energy buffer. As such, storing excess energy in chemical bonds, for example that of hydrogen (H2), is a desirable complementary concept. While hydrogen gas is easily cycled and applied in electrical systems, it brings high costs for long termstorage and transportation. The technical solutions introduce complications in terms of limited equipment lifetime and when applied in combustion systems also safety concerns. An alternative for these applications is to further convert the hydrogen into hydrocarbons such as alkanes and alcohols. Through CO2 hydrogenation, methane can be produced and used in current infrastructure solutions due to it being the major component also in natural gas. While typically produced using nickel based catalysts, other metals such as ruthenium and rhodium have shown promise, of which Rh/CeO2 is one such catalyst. While kinetic studies exist of said catalyst, the reaction mechanism is unknown, which hampers further development. This work aims towards clarifying the catalyst structure-function relationship as well as the important surface reactions. The ambition is to facilitate the start of fundamental research approach, which can later be developed to achieve a more complete understanding, allowing for tuning the important properties of said catalyst.In this work, Rh/CeO2 catalysts were prepared by incipient wetness impregnation and studied in situ during CO2 hydrogenation in regards to its structural behaviour, by the use of high-energy X-ray diffraction and ambient pressure X-ray photoelectron spectroscopy, as well as the surface reactions using diffuse reflectance infrared spectroscopy. As signals from processes and adsorbates that truly participate in the reaction may be hidden by spectator signals, these studies were performed transiently as to enhance the response of active species while decreasing that of spectators.It was revealed that CeO2 is active during reaction conditions, possibly partaking in a cycle of formation and healing of oxygen vacancies during the reaction cycle as evidenced by the cycling of Ce4+ and Ce3+. Furthermore, while predominantly reduced, a RhOx phase was observed, showing the strong metal support interaction of Rh and CeO2. Regarding surface reactions, several carbonyl species (b-CO, h-CO, m-CO) were shown to be active on the catalyst, as well as some carbonates (b-CO3, p-CO3) and formate (b-HCOO) species.While the complete pathway need more experimental data to be determined, the activity of the carbonyl species suggests that the reaction follows a carbon monoxide based pathway such as the carbide pathway

Equidistribution of iterations of holomorphic correspondences and Hutchinson invariant sets

In this paper we analyze a certain family of holomorphic correspondences on $\hat{\mathbb{C}}\times\hat{\mathbb{C}}$ and prove their equidistribution properties. In particular, for any correspondence in this family we prove that the naturally associated multivalued map $F$ is such that for any $a\in \mathbb{C}$, we have that $(F^n)_*(\delta_a)$ converges to a probability measure $\mu_F$ for which $F_*(\mu_F)=\mu_F d$ where $d$ is the degree of $F$. This result is used to show that the minimal Hutchinson invariant set, introduced in [ABS20a], of a large class of operators and for sufficiently large $n$ exists and is the support of the aforementioned measure. We also prove that in this situation the minimal Hutchinson-invariant set is a Cantor set.Comment: Fixed typos, minor change in exposition of the result

Transient In Situ Studies on Supported Catalysts: CO2 Methanation and Methane Oxidation

This dissertation aims to increase the understanding of important steps in the catalytic CO2 hydrogenation and total methane oxidation reactions over supported noble metal catalysts. A general theme is the role of the metal oxide support for the catalytic reactions. In the case of methane oxidation, the reported detrimental effect of water is of primary interest.A range of powder catalysts were prepared by incipient wetness impregnation including Rh/MO (MO = SiO2, Al2O3, CeO2) and Pd/MO (MO = Al2O3 and ZSM-5) for CO2 hydrogenation and methane oxidation, respectively. The catalysts were studied in situ using high-energy X-ray diffraction, ambient pressure X-ray photoelectron spectroscopy and X-ray absorption spectroscopy as to follow structural dynamics and with diffuse reflectance infrared Fourier transform spectroscopy to monitor surface species. Transient measurements were designed and obtained data were analysed with phase sensitive detection in order to distinguish inactive (spectator) species from active ones.For CO2 hydrogenation on the rhodium catalysts, an initial step of dissociation of carbon dioxide into carbon monoxide (and oxygen) occurs on the rhodium phase, and is enabled by the presence of hydrogen. The irreducible supports (SiO2 and Al2O3) show a minor contribution to the catalytic mechanism whereas for the CeO2 based catalysts, several kinds of carbonyls (b-CO, h-CO, m-CO) and carbonates (b-CO3, p-CO3) are active species. While more experimental data is needed as to establish the complete pathway, the activity of the carbonyl species suggests that the reaction follows a carbon monoxide based pathway such as the carbide route.As for the detrimental effect of water on the methane oxidation, two aspects are shown to be of critical importance. The first concerns the build up of a low but strongly inhibiting hydroxyl coverage on the PdO nanoparticles hampering their redox dynamics and seemingly shifting the operating mechanism from a Mars-van Krevelen to a Langmuir-Hinshelwood type of mechanism that proceeds slower. The second is the support hydrophilicity, which contributes to inhibition of important active sites on the rim of the developed PdO nanoparticles through the formation of surface hydroxyls.The knowledge about the catalyst structure-function relationships obtained in this work may be used to guide future catalyst design and synthesis, and catalyst operation, as to provide more efficient catalytic processes

A nearly optimal preconditioner for the Navier-Stokes equations

We present a preconditioner for the linearised Navier-Stokes equations which is based on the combination of fast transform approximation of an advection diffusion problem together with the recently introduced '$BFB^{T}$' preconditioner of Elman (SIAM J. Sci. Comput. 20 pp. 1299-1316, 1999). The resulting preconditioner when combined with an appropriate Krylov subspace iteration method yields the solution in a number of iterations which appears to be independent of the Reynolds number provided a mesh Peclet number restriction holds, and depends only mildly on the mesh size. The preconditioner is particularly appropriate for problems involving a primary flow direction

Evaluation of uptake mechanisms of phosphate by Fe(III)(oxyhydr)oxides in Early Proterozoic oceanic conditions

Banded iron formations (BIF) are proxies of global dissolved inorganic phosphate (DIP) content in Precambrian marine waters. Estimates of Precambrian DIP rely on constraining the mechanisms by which Fe(III)(oxyhydr)oxides scavenge DIP in NaCl solutions mimicking elevated Precambrian marine Si and Fe(II) concentrations. The two DIP binding modes suggested for Early Proterozoic marine waters are 1) surface attachment on pre-formed Fe(III)(oxyhydr)oxides (adsorption), and 2) incorporation of P into actively growing Fe(III)(oxyhydr)oxides (coprecipitation) during the oxidation of Fe(II) to Fe(III)(oxyhydr)oxides in the presence of DIP. It has been suggested that elevated Si concentrations such as those suggested for Precambrian seawater, strongly inhibit adsorption of DIP in Fe(III)(oxyhydr)oxides, however recent coprecipitation experiments show that DIP is scavenged by Fe(III)(oxyhydr)oxides in the presence of Si, seawater cations and hydrothermal As. In this study we show that the DIP uptake onto Fe(III)(oxyhydr)oxides by adsorption is less than 5% of that by coprecipitation. Differences in surface attachment and the possibility of structural capture within the Fe(III)(oxyhydr)oxides are inferred from the robust influence Si has on DIP binding during adsorption, but inhibited for coprecipitation when As(III) and As(V) are present. The data imply that in the Early Proterozoic open oceans, Fe(III)(oxyhydr)oxides precipitated when deep anoxic Fe(II)-rich waters rose and mixed with the first permanently oxygenated ocean surface waters, caused DIP removal from surface waters through coprecipitation rather than adsorption. Local variations in DIP and perhaps even stratification of DIP in the oceans were likely created from the continuous removal of DIP from surface waters by Fe(III)(oxyhydr)oxides, and its partial release into the anoxic bottom waters and in buried sediments. In addition to a DIP famine, the selectivity for DIP over As(V) may have led to As enrichment in surface waters both of which would have most likely decreased the productivity of cyanobacteria and O2 production

Evaluation of pre-harvest forecasts based on harvester data at Sveaskog

För att på ett effektivt sätt styra ett kundanpassat virkesflöde krävs god in-formation om tillgången av virke. Vid en skoglig åtgärd så som gallring eller föryngringsavverkning görs vanligtvis en skattning av detta i fält, vilken sedan även kan kompletteras med en utbytesberäkning. En ny metod att göra utby-tesberäkningar baserade på historiskt skördardata har en kort tid använts inom Sveaskogs verksamhet. Syftet med detta arbete var att utvärdera denna metod att göra utbytesbe-räkningar genom att: 1) kartlägga hur metoden har implementerats i Sve-askogs verksamhet, 2) kvantifiera noggrannheten och precisionen i ingångs-data för utbytesberäkningen och 3) kvantifiera noggrannheten och precis-ionen för utbytesberäkningen. Arbetet har genomförts genom en workshop med insatta personer för att kunna göra en kartläggning av arbetsprocessen där utbytesprognoser tas fram. Sedan har ett datamaterial innehållande alla åtgärder inom ett givet tidsspann studerats för att kunna kvantifiera noggrannheten och precisionen. För den skogliga skattningen har även en regressionsanalys genomförts för att undersöka vilka variabler som bidrar till att avvikelser mellan planerat och avverkad volym uppstår. Resultaten av studien visar att det för de skogliga skattningarna finns vissa systematiska fel, vilka är olika stora för de olika skogliga parametrarna. Fram-förallt stamantal och grundyta utmärker sig genom att visa både något sämre precision och noggrannhet än övriga parametrar. Avvikelser i volym tycks framförallt påverkas av vilket Resultatområde åtgärden tillhör samt åtgärdens volym per ha. Dock visar den framtagna modellen att det finns fler faktorer som kan påverka avvikelsen än vad som tagits med i studien. Imputeringen visar bra noggrannhet men något sämre precision.In order to handle a customized wood flow in an efficient way high quality information about wood resources are important. Before harvests an estima-tion of the stand is usually conducted which then can be complemented with a pre-harvest forecast. A new method to conduct these forecasts based on historical harvester data has been implemented at Sveaskog. The aim of this study was to evaluate these pre-harvest forecasts by: 1) map the work-process of the forecasts, 2) quantify the precision and accuracy of the forestry measurements that are used as input for the forecast and 3) quantify the precision and accuracy for the forecasts. The work has been conducted by arranging a workshop with people work-ing with the forecasts in order to do the mapping. Then a set of data contain-ing all the harvests carried out during a given time period was analyzed to be able to quantify the precision and accuracy. For the forest estimations a re-gression analysis was conducted to see which variables mostly affected the differences between planned and harvested volume. The results from this study show that there are systematic errors for several of the estimated forest variables. Number of stems and basal area had the lowest precision and accuracy. Deviation between planned and harvest vol-ume seems to mostly be affected by the volume per hectare and region. How-ever, the module only explains some part of the deviation. The volumes pre-dicted with historical harvester data show a good accuracy and a lower pre-cision

Musik- och kulturskolans utbud och prioriteringar - Intervjuer med lärare

Den här uppsatsen undersöker lärarnas betydelse för musik- och kulturskolornas utbud och prioriteringar. Den undersöker också deras attityder inom olika områden som skulle kunna ha betydelse för dessa prioriteringar. Undersökningen är gjord enligt kvalitativ metod, genom intervjuer med instrumentallärare vid olika musik- och kulturskolor. Det är mycket som talar för att musiklärare uppfattar att de har ett stort inflytande över beslut som fattas inom musik- och kulturskolan. För det första upplever lärare att musikskolan själv har ett stort inflytande över sin verksamhet och att kollegiet bör vara en viktig grund för de beslut som tas. Lärare uttryckte också starka åsikter om hur musikundervisningen skulle bedrivas och vilket syfte den har. Dessa uppfattningar behöver inte alltid överensstämma med de uppfattningar och förväntningar som elever och deras föräldrar har. Title: Offerings and priorities at the Community Music School/Community School of Culture. Interviews with teachers. The aim of the thesis was to investigate the role instrumental teachers within the community based music- and art schools play in decisions made concerning the range of courses and priorities within schools. It will also investigate opinions and attitudes among the teachers that might influence such priorities. The investigation is conducted using a qualitative method, i.e. by interviewing instrumental teachers. It seems that teachers perceive themselves as having a significant influence on the decisions made within the schools. First of all, the teachers are of the opinion that most decisions are made at the local level of the schools and that the teachers should have an important role to play in influencing such decisions. Teachers also expressed strong opinions on how instrumental education should be exercised and on the long term purpose of this education. Such opinions do not always have to be in accordance with opinions and expectations that pupils and their parents have