Abstract
The goal of the research described in this thesis was to study the amount of noble metals required in bifunctional catalysts for hydroconversion by tuning the nanoparticle location, without compromising the catalytic performance. The catalysts that were studied each contained three main components: (noble) metal (oxide) nanoparticles, zeolite or zeotype
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material, and a binder. In Chapter 2 a new tool for controlling the metal nanoparticle location in Pd/zeolite and Pd/zeotype catalysts is described. We show that performing a direct reduction (DR) on ammonium palladate exchanged zeolites/zeotypes results in enrichment of Pd on the outer surface of the solid acid crystallites, whereas slow calcination followed by reduction (CR) resulted in more Pd nanoparticles being confined inside the zeotype crystallites. The focus in Chapter 3 is on the minimum amount of platinum required as function of Pt nanoparticle location. Two sets of catalysts were prepared: one set was based on mordenite and the other one on ZSM-22. In the set with mordenite the Pt nanoparticles were either inside the mordenite crystallites or on alumina binder. The ZSM-22 set had the Pt nanoparticles either on the ZSM-22 crystallites or on the alumina binder. Pt weight loadings of 0.005 to 0.5 wt% were used. At loadings of 0.01 wt% catalysts with Pt on alumina binder were much less active. Extensive characterization revealed that this was a result of strong metal-support interaction of the Pt clusters with alumina. Since the lower catalytic performance of Pt-on-alumina with ≤ 0.01 wt% Pt loadings in Chapter 3 was a result of γ-alumina lacking chemical inertness, we explored the replacement of this binder by silica in Chapter 4. Catalysts with 0.005 to 0.5 wt% Pt on ZSM-22 or on silica were prepared and characterized. These catalysts were then applied in the hydroconversion of n-heptane. Moreover, for the first time the effect of the low loadings on the catalytic performance during n-hexadecane was assessed. Diminishing noble metal utilization could also mean replacement with earth abundant metals. Chapter 5 is dedicated to an exploration of nickel based bifunctional catalysts for hydroconversion. We show that Ni based catalysts typically display high hydrogenolysis activity to produce mainly methane. However, the combination of the use of n-alkanes with higher molecular weight (e.g. n-hexadecane) and emplacing Ni (oxide) nanoparticles at the right place could reduce hydrogenolysis activity and improve i-hexadecane selectivity. Lastly, Chapter 6 provides a summary & outlook and ‘een Nederlandse samenvatting’ (Dutch summary).
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