Nanomaterials for membranes and catalysts
Sammanfattning: Nanotechnology is a relatively new research topic that attracts increasing interest from scientists and engineers all over the world, due to its novel applications. The use of nanomaterials has extended to a broad range of applications, for example chemical synthesis, microporous media synthesis and catalytic combustion, contributing to achievement of improved or promising results. Microemulsion (ME) is considered a powerful tool for synthesis of nanomaterials, due to its unique properties. This thesis concentrates on the use of the ME as a catalyst synthesis route for obtaining metal nanoparticles for two challenging concepts: Hydrogen production by a membrane reactor and selective catalytic oxidation (SCO) of ammonia in gasified biomass.Particularly for the scope of the fist concept presented in this thesis, palladium nanoparticles were synthesised from ME in order to be deposited on zeolite composite membranes to improve the H2 / CO2 separation (hydrogen production) ability. The membranes impregnated with Pd nanoparticles were then tested in a metal reactor for the permeance and selectivity towards H2 and CO2. Regarding the second concept, cerium-lanthanum oxide nanoparticles were prepared by conventional methods and from ME in order to be tested for their activity towards SCO of ammonia in gasified biomass.The environmental importance of these two applications under investigation is great, since both are involved in processes contributing to the minimisation of the harmful exhaust gases released to the atmosphere from numerous industrial applications, such as the oil industry and heat-and-power production (for example combustion of natural gas or biomass in a gas turbine cycle). Regarding these applications, separation and capture of CO2 from exhaust gases and oxidation of the fuel-bound ammonia in gasified biomass directly to nitrogen, minimising at the same time NOx formation, are rated as very important technologies. The results obtained from this work and presented analytically in this thesis are considered successful and at the same time promising, since further research on the ME method can even lead to improvement of the current achievements.The first part (Chapter 2) of the thesis gives a general background on the ME method and the applications in the two concepts under investigation. Additionally, it describes how the nanoparticles corresponding to the concepts were synthesised.The second part (Chapter 3) of the thesis describes the different Pd-nanoparticle impregnation methods on the zeolite composite membranes and the results obtained form the permeation tests. In parallel with impregnation methods, various aspects that affect the Pd impregnation efficiency and the membrane performance such as duration, temperature and calcination conditions are discussed thoroughly.The third and final part of the thesis (Chapter 4) concerns the preparation of the cerium-lanthanum oxide catalysts and the activity tests (under simulated gasified biomass fuel conditions) carried out in order to monitor the activity of these catalysts towards the SCO of ammonia. Additionally, a comparison of the activity between identical catalysts prepared by conventional methods and the ME method is discussed.
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