Duchstein, Linus Daniel Leonhard

I hele verden bliver naturressourcer som råolie mindreog mindre tilgængelige. Vi er derfor nødt til at finde alternativer til at sikre brændstof til bl.a. transport i fremtiden på en bæredygtig måde. Initiativet ’Catalysis for Sustainable Energy’ (CASE) ved Danmarks Tekniske Universitet (DTU) er iværksat til at finde bæredygtige alternativer til at generere og lagre energi. En mulighed er at transformere lignocellulose som er et affaldsprodukt fra landbrug til bioalkohol, som kan bruges allerede i dag som et alternativ til benzin i biler. Det gør man ved at gasificere lignocellulose ind i en syntesegas (H2og CO eller CO2) og derefter reformere gassen til alkohol. Vi har dog brug for bedre katalysatorer til at konvertere syntesegassen til alkohol mere effektivt.  To katalyse systemer er blevet identificeret som aktiv til den katalytiske konvertering: CuNi og NiGa. Begge er blevet syntesiseret fra Cu og Ni eller Ni og Ga nitrat salte. De er blevet undersøgt for deres katalytiske ydelse og krystalstrukturer under syntese fra nitrat salte i H2atmosfære og under reaktionsbetingelser i syntese gas. Et ”Environmental Transmission Electron Microscope” (ETEM) er brugt til at undersøge katalysatorerne på et atomar niveau mens de er i en gas atmosfære i mikroskopet i op til 4,5 mbar tryk. Desuden bliver CuNi og NiGa undersøgt med in-situXRD som giver informationer om krystalstrukturer i hele prøven. Med begge metoder er der fundet, at CuNi danner nanopartikler af en substitutionslegering af Cu og Ni. NiGa danner nanopartikler i en Ni5Ga3legering. ETEM viser morfologiske ændringer i nanopartiklerne når de bliver udsat for H2til syntetisering og H2og CO2når de bliver brugt i syntesegas.  Derudover bliver det også undersøgt hvordan elektronstrålen i et ETEM påvirker prøven. Hvis man ser ændringer eller reducering i krystalstrukturen, skal de helst ikke være på grund af elektronstrålen. Derfor bliver CuNi udsat for tre forskellige intensiteter af elektronstrålen ved tre forskellige temperaturer, mens reduktionen af Cu2+ bliver målt. Elektronstrålens påvirkning er ikke entydigt afhængig af intensiteten, men derimod hvor længe prøven bliver udsat for elektronstrålen.  PhD projektet er blevet finansieret af initiativet ’Catalysis for Sustainable Energy’ fra det Danske ministerium for forskning, innovation og videregående uddannelser. Center for elektronnanoskopi (Cen) er blevet finanseret af en donation fra A. P. Møller og Chastine McKinney Møller fonden.Everywhere around the world, natural resources like crude oil are becoming less and harder to extract. It is therefore necessary to find alternatives to secure our future transportation in a sustainable way. This can be done e.g. through chemical conversion of lignocelluloses into bio-alcohol through syngas (H2and CO or CO2). Cars can already today use alcohol in their combustion engine and the existing infrastructure for fuel distribution can be used without modifications. But therefore we need better and more efficient catalysts to convert the syngas into the alcohol. The Catalysis for Sustainable Energy (CASE) initiative at the Technical University of Denmark (DTU) was founded to find solutions to some of these challenges, among them also new catalysts for the alcohol synthesis out of syngas.  Two catalytical systems were identified to be active for the Methanol synthesis: CuNi and NiGa. Both were synthesized from Cu and Ni nitrate salts as well as Ni and Ga nitrates salts. Both systems got catalytically tested and investigated by in-situ X-Ray Diffraction (XRD) and Environmental Transmission Electron Microscopy (ETEM). It was possible to follow the synthesis of the catalysts and the reaction of the catalysts as they were happening and study crystal phase changes as well as chemical shifts because the instruments are capable of introducing gases around the sample while still maintaining their investigation properties. It could be shown, that NiGa forms Ni5Ga3nanoparticles while CuNi forms a substitutional alloy. During the reaction and artificial ageing a deactivation of the NiGa due to a phase change could be observed. CuNialso changes the the oxidation state during the reaction.  Furthermore the influence of the electron beam on the catalytic systems during exposure to gas atmosphere and temperature was investigated. CuNi was exposed to the electron beam for 3 different intensities and 3 different temperatures while the oxidation state of the Cu2+ was measured by energy electron loss spectroscopy. It turns out that the electron beam does have an influence but it does not seem to scale with the beam current density but foremost with the exposure time. The ETEM shows phase and chemical changes during the reaction.</p

Online Research Database In Technology

Environmental Transmission Electron Microscopy of catalysts for the methanol synthesis

http://orbit.dtu.dk/ws/files/74207351/Linus_Duchstein_PhD_thesis..PDF

Environmental Transmission Electron Microscopy of catalysts for the methanol synthesis

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