Tuning catalyst stability by surface functionalisation
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The support material in heterogeneous catalysts plays a pivotal role in stabilising metal nanoparticles which form the active phase in the catalysts. It influences and can suppress the growth of the metal nanoparticles in catalysts. Because of this, the support has influence on the quantity of the active phase in the catalyst. Catalysts will become less efficient when the quantity of active phase available for reaction decreases and when the activity drops below a certain level, the catalyst needs to be replaced. This study focuses on how the growth of metal nanoparticles is influenced by the chemical nature of the support of the catalyst. The study focuses on a methanol synthesis catalyst. The activity of the industrially used methanol synthesis catalyst, a Cu/ZnO/Al2O3 catalyst, decreases over time due to growth of the copper particles. Since world’s demand for methanol is increasing every year, one should keep optimising the methanol synthesis process and look for a more stable catalyst. A model Cu/SiO2 methanol synthesis catalyst is used this study. The chemical properties of the support of the model Cu/SiO2 catalyst were changed by functionalisation or grafting of the support with amino groups, methyl groups, alumina, titania and zinc oxide. The functionalised and grafted catalysts were studied with DRIFTS, N2 physisorption, ICP, TEM, EDX spectroscopy and the catalyst activity and deactivation in methanol synthesis was tested in a catalytic test of 230 hours. The introduction of amino groups on the support was found to stabilise the copper nanoparticles and suppress the particle growth in the catalyst. Methyl groups changed the deactivation behaviour of the catalyst. Alumina and titania have acidic properties. Grafting with these metal oxides resulted in the dehydration of methanol towards DME. Next to this, titania was also found to migrate on the copper particles reducing active surface area caused by the SMSI properties it exhibits. Grafting with alumina, titania and zinc oxide resulted in stronger deactivating catalysts.