Micro-kinetic modeling of NH3 decomposition on Ni and its application to solid oxide fuel cells

This paper presents a detailed surface reaction mechanism for the decomposition of NH3 to H2 and N2 on a Ni surface. The mechanism is validated for temperatures ranging from 700 to 1500K and pressures from 5.3Pa to 100kPa. The activation energies for various elementary steps are calculated using the unity bond index-quadratic exponential potential (UBI-QEP) method. Sensitivity analysis is carried out to study the influence of various kinetic parameters on reaction rates. The NH3 decomposition mechanism is used to simulate SOFC button cell operating on NH3 fuel

Kinetic modeling and simulation of high-temperature by-product formation from urea decomposition

The Selective catalytic reduction (SCR) technique is widely applied in exhaust gas after-treatment of diesel engines. Depending on operating conditions, injected urea-water solution (UWS) can form liquid films on mixer blades and the pipe wall. Evaporation and subsequent reactions in the wall film can lead to deposits of urea and by-products, respectively. Especially deposits that are not decomposed up to high temperatures are challenging for the SCR technique. Thermogravimetric experiments are conducted for these stable urea by-products, such as ammelide, ammeline and their by-products, such as cyanamide or melamine. An analysis of the evolving gases during thermal decomposition led to a more detailed understanding of the kinetics. The postulated mechanism is able to predict the thermogravimetric analyses results and the effects of variation of the experimental conditions such as initial sample mass and heating rates. The evaluated kinetics, together with the recently developed kinetics for the urea/biuret/triuret/cyanuric acid system Tischer et al. (2019), can now be integrated into CFD simulations of SCR systems to numerically simulate all relevant physical and chemical processes in UWS equipped aftertreatment systems for a wide range of conditions

Iron as recyclable energy carrier: Feasibility study and kinetic analysis of iron oxide reduction

Carbon-free and sustainable energy storage solutions are required to mitigate climate change. One possible solution, especially for stationary applications, could be the storage of energy in metal fuels. Energy can be stored through reduction of the oxide with green hydrogen and be released by combustion. In this work a feasibility study for iron as possible metal fuel considering the complete energy cycle is conducted. On the basis of equilibrium calculations it could be shown that the power-to-power efficiency of the iron/iron oxide cycle is 27 %. As technology development requires a more detailed description of both the reduction and the oxidation, a first outlook is given on the kinetic analysis of the reduction of iron oxides with hydrogen. Thermogravimetric experiments using Fe$_2$O$_3$, Fe$_3$O$_4$ and FeO indicate a three-step process for the reduction. The maximum reduction rate can be achieved with a hydrogen content of 25 %. Based on the experimental results a reaction mechanism and accompanied kinetic data were developed for description of Fe$_2$O$_3$ reduction with H$_2$ under varying experimental conditions

Influência dos diferentes solventes na avaliação da capacidade antioxidante in vitro de frutos e sementes de pitaia (Hylocereus polyrhizus)

A pitaia (Hylocereus polyrhizus) é um fruto que tem ganhado destaque devido as características peculiares deste fruto e aos compostos bioativos em sua composição. Portanto, o presente trabalho buscou verificar o conteúdo de compostos fenólicos totais e capacidade antioxidante  in vitro de frutos e sementes de pitaia produzidos e coletados em Santa Catarina, buscando avaliar solventes e sistemas de extração. No preparo das amostras, as sementes foram desidratadas triturados e as sementes lavadas, secas e trituradas. Em seguida, foram submetidas a dois sistemas de extração, agitação por rotação em geladeira e ultrassom, ambos por 1h e utilizados dois solventes diferentes, acetona 80% e metanol 0,1% HCl. Para o fruto inteiro, observa-se que para fenólicos totais e capacidade antioxidante não houve diferença significativa entre os métodos de extração em relação ao solvente metanol 0,1% HCl. Já entre diferentes solventes observa-se que os maiores valores foram para metanol 0,1% HCl, indicando ser o solvente de extração mais eficiente para o fruto pitaia. Já para a semente desidratada, os teores de fenólicos totais não diferiam estatisticamente entre os métodos de extração para cada solvente, sendo que os maiores valores foram para metanol 0,1% HCl. Para capacidade antioxidante por ambos os métodos, o melhor sistema de extração foi ultrassom e a acetona 80%. Os maiores valores de fenólicos totais e capacidade antioxidante foram encontrados para semente desidratada. 

Nanoscale temperature measurements using non-equilibrium Brownian dynamics of a levitated nanosphere

Einstein realised that the fluctuations of a Brownian particle can be used to ascertain properties of its environment. A large number of experiments have since exploited the Brownian motion of colloidal particles for studies of dissipative processes, providing insight into soft matter physics, and leading to applications from energy harvesting to medical imaging. Here we use optically levitated nanospheres that are heated to investigate the non-equilibrium properties of the gas surrounding them. Analysing the sphere's Brownian motion allows us to determine the temperature of the centre-of-mass motion of the sphere, its surface temperature and the heated gas temperature in two spatial dimensions. We observe asymmetric heating of the sphere and gas, with temperatures reaching the melting point of the material. This method offers new opportunities for accurate temperature measurements with spatial resolution on the nanoscale, and a new means for testing non-equilibrium thermodynamicsComment: 5 pages, 4 figures, supplementary material available upon reques