Novel Ni5Ga3 and Pd2Ga catalysts for CO2 hydrogenation to methanol are prepared by impregnation of aqueous Ni-Ga or Pd-Ga solutions of metal nitrates into high surface area SiO2, followed by drying, calcinations and reduction of the precursor in a H2 flow. Steady state experiments are performed in a reactor at atmospheric pressure and stoichiometric CO2/H2 mixture, while reaction products are analyzed by gas chromatography. The results are compared to the highly optimized Cu/ZnO/Al2O3. The activity and selectivity of the novel catalysts is close to that of Cu/ZnO/Al2O3 and the equilibrium conversion to CH3OH is found to be higher. XRD and XRF are used to investigate the phase and composition of the supported catalysts at the 5 stages of testing, i.e. after drying, calcination, reduction, CO2 hydrogenation, rapid ageing. SEM and TEM images of the exact same locations are acquired after each of the 5 stages to monitor particle formation and investigate particle size and distribution. In the same way, model systems consisting of Ni5Ga3 and Pd2Ga nanoparticles supported directly on a silica membrane of an Au TEM grid are also characterized by SEM and TEM after each of the 5 stages. Nanoparticles formation is observed after calcination. Size distribution analysis reveals that the Pd2Ga nanoparticles have a diameter of 5-10 nm which does not change after reduction, methanol synthesis and rapid ageing. Furthermore, in situ ETEM is used to monitor the development of the materials system during synthesis and reaction.
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Scandem 2013 - Annual Meeting of the Nordic Microscopy Society