Design of porous nanostructured solid catalysts

Jacob Oskar Abildstrøm

Research output: Book/ReportPh.D. thesisResearch

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Abstract

This thesis aims at developing and characterize novel porous nanostructered materials for heterogeneous catalysis. The catalysts are prepared with the goals of increased activity and stability in mind. This will result in lessened waste of precious elements, starting materials, and energy, for a more sustainable chemical industry. Chapter 1 gives a short introduction to the eect of heterogeneous catalysis upon the current chemical industry. The scope of the thesis will also be sketched. Chapter 2 is a description of the methods used in the thesis, to characterize the materials produced. These include X-ray powder diraction, physisorption analysis, and electron microscopy. This include common use, and possible pitfalls. Chapter 3 is an introduction to zeolites and their properties, mainly shape selectivity and catalytic activity. The diusion limitations imposed by the porous system in zeolites will be examined as well, and strategies on how to overcome this limitations will be presented. Chapter 4 describes the synthesis of mesoporous zeolites with a carbon secondary hard template. The carbon is generated through the decomposition of methane over nickel nanoparticles. This is done as an in situ process, directly upon the silica source for the zeolite. This method is signicantly cheaper than previously reported for carbon templates. This increases the feasibility of utilizing mesoporous zeolites for various applications. The mesoporous zeolite possessed a greater total pore volume, while still matching its conventional counterpart in terms of crystallinity and acidity. Samples of conventional and mesoporous zeolites were tested in a model catalytic reaction. Here, the mesoporous zeolite exhibited much higher conversion, which is contributed to the enhanced diffusion. Chapter 5 explains the fundamentals of fuel cells, as a mean to transform chemical as the main technique explained. The chapter will also cover degradation mechanisms of the catalyst employed in PEMFC, such as carbon corrosion and particle agglomeration. Strategies on how to increase resistance towards these degradation mechanisms, such as particle encapsulation, employing graphitic support, and heteroatom doping, will be described. Lastly, a possible PEMFC catalyst based on platinum dispersed on a nanoporous polymer is reported. Chapter 6 is the examination of a novel catalyst for PEMFC. The synthesis strategy aims at high durability and activity. The basis of the catalyst is the yolk-shell particles consisting of small platinum nanoparticles and a shell of nitrogen doped carbon with graphitic elements. The carbon shell will be activated with potassium hydroxide to generate some microporosity in the shell, to improve the diffusion of reactants. The catalyst is extensively characterize with respect to both the platinum nanoparticles and the carbon shell. Lastly the catalyst is employed in the electrooxidations of methanol, ethanol, and formic acid.
Original languageEnglish
PublisherDTU Chemistry
Number of pages123
Publication statusPublished - 2016

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