Bjørn Gading Solemsli

Hydrogenation of carbon dioxide hasreceivedincreasingattentionin catalytic research the last decade as a sustainable alternativeforproducing high value chemicals thattodayare produced fromfossil fuels. The aim of this thesis has been two-fold: First, to study Pt nanoparticles formed in various UiO-66 and -67 metal-organic frameworks (MOFs) by Transmission Electron Microscopy (TEM), and second, to study the Pt-containing MOFs as catalysts for the CO2hydrogenation reaction.Three Zr-based UiO-66 MOF and nineUiO-67 MOF samples containing different amountsof functionalized linkers were impregnated withdifferent amounts ofK2PtCl4and reduced in H2at 350 ̊C for 4 hours to form Pt nanoparticles embedded in the MOF matrix.The samples were then testedin a H2/CO2feed at 8 bar and 170 ̊Cfor the hydrogenation reaction. After testing,TEMwas used to investigate the formation of Pt nanoparticles andtheir relationship with the surrounding MOF structure. The study revealed that, despite variable the linkers in the MOF,the conversion of CO2isdominated bythe reverse water-gas shift reaction,suggestingthat the linkers donot partakethe reactions mechanisms. Analysis usingTEMrevealedthat the Pt nanoparticles grow independently of its surroundings inside the MOFs with no observable growth relationshipwith the MOF. The nanoparticles are seen to grow into octahedral crystals that are larger than the pores in the framework. Samples with different amountsof missing linker type defects show that the presence of open Zr-node sitesenhances the selectivity towards methanol. A sample of Pt-functionalized UiO-67 with 10% [2,2’-bipyridine]5,5’-dicaboxylicacidlinker was oxidised toinduce missing linkerdefects post synthetically. After reduction in H2at 350 ̊C for 4 hours, the sample was oxidized in situin synthetic air for three different time spans. Careful analysis with N2-adsroption and TEM revealedthat the structure of the MOF deteriorates and loses accessible surface area with increasing timeon steam, while keeping the dispersion of the Pt nanoparticles. PXRD analysis revealedthe formation of tetragonal ZrO2. Extensive testsfrom 1-30 bar and 170-375 ̊C reveal a lower conversion and higher selectivity towards methanol for a fully calcined sample, indicating that the Zr-nodes behave similarlyto non-MOF ZrO2supports. Transient kinetic studies of the parent UiO-67 sample revealedthat the sample behaves similarlytopreviously studied systemsby Gutterød et al., and showed the presence of an inverse kinetic isotope effect for methane and methanolformation upon H2/D2exchange.