Browsing by Author "Santi, Dominic"

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    Hydroconversion of cis-decalin on noble metal-containing zeolites
    (2012) Santi, Dominic; Weitkamp, Jens (Prof. Dr.-Ing.)
    There has recently been considerable concern about polynuclear aromatic hydrocarbons in diesel fuel, as they have a variety of unfavorable properties like low cetane numbers, poor cold-flow properties, propensity of soot formation and high specific CO2 emissions. The conversion of such polynuclear aromatic hydrocarbons into hydrogen-rich, environmentally benign blending cuts for diesel fuel continues to be among the challenges of heterogeneous catalysis. In the best case, such a conversion would lead to alkanes with the same carbon number as the polynuclear aromatic hydrocarbons. This route would comprise two steps, namely the complete hydrogenation of the aromatic rings to naphthenes followed by their selective ring opening to alkanes. While the first step is generally considered as state-of-the-art catalysis, the selective ring opening continues to be a challenge in today’s catalysis research. In this thesis, the influence of the nature of the noble metal, the structure of the zeolite catalysts and their acidic properties on the selective ring opening of cis-decalin was studied, and a catalytic system was developed which enables unprecedented selectivities and yields of open-chain decanes (OCDs). Different noble metals (ruthenium, rhenium, palladium and rhodium) supported on the faujasite Na,H-Y were investigated to identify the best suited noble metal for this reaction. As already known from literature, iridium and platinum supported on faujasites are very promising catalysts for this reaction: Maximum yields of OCDs as high as 31 and 39 %, respectively, had been described. Since none of the evaluated noble metals showed better results all subsequent experiments were conducted on catalysts containing either iridium or platinum. To investigate the influence of the zeolite structure on the selectivities and yields to OCDs, different types of 12-membered ring pore zeolites (Na,H-mordenite, K,H-L, H-SAPO-5, Na,H-EMC-2, Na,H-[Al]Beta-14 and Na,H-ZSM-5) were loaded with about 3 wt. % of platinum or iridium and tested in the hydroconversion of decalin. To examine the influence of the Brønsted acid sites on the reaction, the strengths of the sites were varied in three different ways, namely (i) the isomorphous substitution of aluminum by boron in zeolite Beta, (ii) the variation of the molar ratio nSi / nAl, again in zeolite Beta, and (iii) the exchange of the charge-compensating cations by different alkali metals in zeolites Beta, mordenite and L. The strengths of the Brønsted acid sites were determined by FT-IR spectroscopy and pyridine as a probe molecule. The best catalyst obtained through these variations was 3.4Ir/H0.58,Cs0.42-[Al]Beta-14, leading to selectivities and yields of OCDs as high as 47 % and 43 %, respectively.