Dynamics of Reactive Oxygen Species on Cobalt-Containing Spinel Oxides in Cyclic CO Oxidation

Reactive oxygen species (ROS) are considered to be responsible for the high catalytic activity of transition metal oxides like Co3-xFexO4 in oxidation reactions, but the detailed influences of catalyst composition and morphology on the formation of these reactive oxygen species are not fully understood. In the presented study, Co3O4 spinels of different mesostructures, i.e., particle size, crystallinity, and specific surface area, are characterized by powder X-ray diffraction, scanning electron microscopy, and physisorption. The materials were tested in CO oxidation performed in consecutive runs and compared to a Co3-xFexO4 composition series with a similar mesostructure to study the effects of catalyst morphology and composition on ROS formation. In the first run, the CO conversion was observed to be dominated by the exposed surface area for the pure Co-spinels, while a negative effect of Fe content in the spinels was seen. In the following oxidation run, a U-shaped conversion curve was observed for materials with high surface area, which indicated the in situ formation of ROS on those materials that were responsible for the new activity at low temperature. This activation was not stable at the higher reaction temperature but was confirmed after temperature-programmed oxidation (TPO). However, no activation after the first run was observed for low-surface-area and highly crystalline materials, and the lowest surface-area material was not even activated after TPO. Among the catalyst series studied here, a correlation of small particle size and large surface area with the ability for ROS formation is presented, and the benefit of a nanoscaled catalyst is discussed. Despite the generally negative effect of Fe, the highest relative activation was observed at intermediate Fe contents suggesting that Fe may be involved in ROS formation

Mesoporous Co 3 O 4 as an electrocatalyst for water oxidation

ABSTRACT Mesoporous Co 3 O 4 has been prepared using porous silica as a hard template via a nanocasting route and its electrocatalytic properties were investigated as an oxygen evolution catalyst for the electrolysis of water. The ordered mesostructured Co 3 O 4 shows dramatically increased catalytic activity compared to that of bulk Co 3 O 4 . Enhanced catalytic activity was achieved with high porosity and surface area, and the water oxidation overpotential (η) of the ordered mesoporous Co 3 O 4 decreases significantly as the surface area increases. The mesoporous Co 3 O 4 also shows excellent structural stability in alkaline media. After 100 min under 0.8 V (versus Ag/AgCl) applied bias, the sample maintains the ordered mesoporous structure with little deactivation of the catalytic properties

Serpentinization: Connecting geochemistry, ancient metabolism and industrial hydrogenation

Rock–water–carbon interactions germane to serpentinization in hydrothermal vents have occurred for over 4 billion years, ever since there was liquid water on Earth. Serpentinization converts iron(II) containing minerals and water to magnetite (Fe3O4) plus H2. The hydrogen can generate native metals such as awaruite (Ni3Fe), a common serpentinization product. Awaruite catalyzes the synthesis of methane from H2 and CO2 under hydrothermal conditions. Native iron and nickel catalyze the synthesis of formate, methanol, acetate, and pyruvate—intermediates of the acetyl-CoA pathway, the most ancient pathway of CO2 fixation. Carbon monoxide dehydrogenase (CODH) is central to the pathway and employs Ni0 in its catalytic mechanism. CODH has been conserved during 4 billion years of evolution as a relic of the natural CO2-reducing catalyst at the onset of biochemistry. The carbide-containing active site of nitrogenase—the only enzyme on Earth that reduces N2—is probably also a relic, a biological reconstruction of the naturally occurring inorganic catalyst that generated primordial organic nitrogen. Serpentinization generates Fe3O4 and H2, the catalyst and reductant for industrial CO2 hydrogenation and for N2 reduction via the Haber–Bosch process. In both industrial processes, an Fe3O4 catalyst is matured via H2-dependent reduction to generate Fe5C2 and Fe2N respectively. Whether serpentinization entails similar catalyst maturation is not known. We suggest that at the onset of life, essential reactions leading to reduced carbon and reduced nitrogen occurred with catalysts that were synthesized during the serpentinization process, connecting the chemistry of life and Earth to industrial chemistry in unexpected ways

Advancing critical chemical processes for a sustainable future: challenges for industry and the Max Planck-Cardiff centre on the fundamentals of heterogeneous catalysis (funcat)

Catalysis is involved in around 85 % of manufacturing industry and contributes an estimated 25 % to the global domestic product, with the majority of the processes relying on heterogeneous catalysis. Despite the importance in different global segments, the fundamental understanding of heterogeneously catalysed processes lags substantially behind that achieved in other fields. The newly established Max Planck–Cardiff Centre on the Fundamentals of Heterogeneous Catalysis (FUNCAT) targets innovative concepts that could contribute to the scientific developments needed in the research field to achieve net zero greenhouse gas emissions in the chemical industries. This Viewpoint Article presents some of our research activities and visions on the current and future challenges of heterogeneous catalysis regarding green industry and the circular economy by focusing explicitly on critical processes. Namely, hydrogen production, ammonia synthesis, and carbon dioxide reduction, along with new aspects of acetylene chemistry

A hydrogen-dependent geochemical analogue of primordial carbon and energy metabolism

Hydrogen gas, H2, is generated by alkaline hydrothermal vents through an ancient geochemical process called serpentinization in which water reacts with iron containing minerals deep within the Earth's crust. H2 is the electron donor for the most ancient and the only energy releasing route of biological CO2 fixation, the acetyl-CoA pathway. At the origin of metabolism, CO2 fixation by hydrothermal H2 within serpentinizing systems could have preceded and patterned biotic pathways. Here we show that three hydrothermal minerals—greigite (Fe3S4), magnetite (Fe3O4) and awaruite (Ni3Fe)—catalyse the fixation of CO2 with H2 at 100°C under alkaline aqueous conditions. The product spectrum includes formate (up to 200 mM), acetate (up to 100 µM), pyruvate (up to 10 µM), methanol (up to 100 µM), and methane. The results shed light on both the geochemical origin of microbial metabolism and on the nature of abiotic formate and methane synthesis in modern hydrothermal vents

Nükleer reaktör malzemelerinin araştırılması

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Yedi bölümden oluşan bu çalışma; kurulması karmaşık işlemler sonucundagerçekleşen nükleer güç reaktörlerinde, enerji üretilen yakıtların ve bunlarınkonulduğu reaktör kalbinin yapımında kullanılan malzemelerin araştırılmasınıiçermektedir.Birinci bölümde, nükleer enerji ve nükleer reaktörlerin elemanları hakkında bilgilerverilmiştir.kinci bölümde, reaktörlerde enerjiyi üretmek için kullanılacak uranyum, toryum veplütonyum yakıtlarının cevher aşamasından reaktörde kullanım aşamasına kadarüretimlerinden bahsedilmiştir.Üçüncü bölümde, üretilen yakıtların konulduğu reaktör kalbinin yapılabileceğialüminyum, magnezyum, zirkonyum, paslanmaz çelik ve seramik malzemelerintüm özelliklerini içeren bilgiler sunulmuştur.Dördüncü bölümde, reaktör kalbinde fisyon sonucunda açığa çıkan yüksek enerjilinötronları yavaşlatmada kullanılan hafif su, ağır su, grafit, berilyum ve berilyumoksit gibi moderatör malzemeler ayrıntılı bir biçimde incelenmiştir.Beşinci bölümde, reaktör kalbinde oluşan fazla nötronları yutmada kullanılan bor-bor ürünleri ve kadmiyumdan yapılan malzemelerle ilgili bilgiler verilmiştir.Altıncı bölüm, reaktörde oluşan ısıyı çekip almada kullanılan gaz, sıvı ve sıvı-metalsoğutucu malzemelerle ilgili bilgileri; yedinci ve son bölüm ise, bütün bumalzemelerin fiziksel ve kimyasal özellikleri dikkate alınarak bir yerde kurulacaknükleer güç reaktörünün çalıştırılması için kullanılacak yakıt, yapı, yavaşlatıcı,kontrol ve soğutucu malzemelerin neler olması gerektiği hakkında bilgileri içerir.ixThis study formed seven sections, contains searching about the fuels used toproduce energy in the nuclear power reactors which need complex operations to beestablished and searching the materials which the reactor?s heart is made of andwhere the fuels are put in.In the first part, nuclear energy and the datas about nuclear reactors? elements havebeen given.In the second part, uranium, torium and plutonium fuels which will be used toproduce energy in the reactors , and how to produce that fuels from ore process tousing in the reactor process have been mentioned.In the third part, the datas about all features of aluminium, magnesium, zirkonium,stainless steel and ceramics with whom the reactor?s heart where the producedmaterials are put in, will be able to built, have been presented.In the fourth part, moderator materials like light water, heavy water, graphite,beryllium and beryllium oxide are used to retard high energied neutrons which aregot after fusion in the reactor?s heart, have been examined.In the fifth part, the datas about the materials made of boron-boron products andcadmium used to absorb extra neutrons formed in the reactor?s heart, have beengiven.The sıxth part contains the datas about gas, liquid and liquid-metal cooler materialsare used to draw the heat formed in the reactor; The seventh, the last part containsthe datas about how to choose the fuels, structure, retarding, control and coolermaterials will be used to be started the nuclear power reactor which will beestablished on a place in according to pay attention to the physical and chemicalfeatures of all these materials.

Novel mesostructured metal oxides

Im Rahmen dieser Arbeit wurden mittels Hard- und Soft-templating diverse mesoporöse, geordnete Siliziumoxide, sowie andere Metalloxide hergestellt. Mittels hochauflösender Rasterelektronenmikroskopie (HR-SEM) wurden detaillierte Studien zur Oberflächen-topologie von bekannten, geordneten, mesoporösen Siliziumoxiden (SBA-15, MCM-41 und KIT-6) durchgeführt. Erstmalig gelang auch die Herstellung von geordnetem, mesoporösen CoO, Co$_{3}$O$_{4}$/CoFe$_{2}$O$_{4}$ und Ferrihydrit über die Nanocasting-Route. Struktur, Topologie, katalytische Aktivitäten und magnetische Eigenschaften dieses Metaloxidgemischs wurde detailliert untersucht. Hierbei stellte sich Co$_{3}$O$_{4}$ als exzellenter Katalysator für die Tieftemperaturoxidation von Kohlenmonoxid heraus. Die katalytische Aktivität war dabei Abhängigkeit von spezifischer Oberfläche sowie Porensystem