Environmental Transmission Electron Microscopy of catalysts for the methanol synthesis

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.