Decane isomerization, zeolite

For n-decane isomerization, when a good balance between the metal phase and the acidic phase of the catalysts is reached, the isomerization and cracking yield curves of the catalysts are a unique function of the conversion, meaning that these yields do not depends on the porosity nor the acidity of large pore materials. Formation of the most bulky isomers, such as 4-propylheptane and 3-ethyl-3-methylheptane was favored in mesoporous solids (figure 1). Criteria based on the formation of these particular isomers are linked with mesoporosity and could be useful to discriminate between zeolites catalysts with and without mesopores. 

When metal centers act in conjunction with acid sites on the zeolite, bifunctional catalysis can occur (e.g., Pd/HY). This type of catalysis is used mainly for the hydrocracking and isomerization of long-chain n-alkanes. For example, the rates of formation of 2- and 5-methylnonane isomers obtained from n-decane isomerization over bifunctional zeolite catalysts depend on the size and structure of the zeolites used. This reaction has been developed as a test reaction to characterize zeolite structures (17-19). 

Remy, M.J., Stanica, D., Poncelet, G., Feijen, E.J.P., and Grobet, P. Dealuminated H-Y zeolites relation between physicochemical properties and catalytic activity in heptane and decane isomerization. J. Phys. Chem. 1996, 100, 12440-12447. 

A synergistic effect was observed for the hydroisomerization of n-decane with intimately mixed Pt/ZSM-22 and deep-bed steamed zeolite NH4Y (311). The synergism is rationalized in terms of a two-step isomerization mechanism. Pt/ZSM-22 converts decane selectively into 2-methylnonane, even at high conversion. The Y sieve receives this 2-methylnonane as its feed inside this Pt-free sieve a high concentration of monobranched alkenes will build up. This enhances their subsequent conversion to multibranched alkenes. 

On the other hand, R-exchanged zeolites have also been used in combination with a metal function, for carrying out the isomerization and hydrocracking of paraffins and cycloalkanes. This is the case for isomerization of n-hexane to isohexane and 2,2-dimethyl-butane (Rabo et al. 1961) the isomerization of n-undecane to mixed Ci 1 isomers at 275°C on Pt/Ce-Y zeolite (Weitkamp et al. 1985) the isomerization of c (7o-exo-tricyclo[5.2.1.02,6]-decane or exo-tricyclo[6.2.1.02,7]-undecane into adamantane or 1-methyladamantane, respectively, on R-Y at 150-270°C (Lau and Maier 1987) the isomerization of tetrahydrodicyclopentadiene into adamantane on Re-Y in a H2/HC1 atmosphere at 250°C (Honna et al. 1986) or the double bond relocation of 2-alkyl acrolein into fran.j-2-methyl-2-alkenals over Ce,B-ZSM-5 (Fisher et al. 1986). Recently, it has been reported that Ce-promoted Pd/ZSM-5 is an active and selective catalyst in the dehydroisomerization of a-limonene to / -cymene (Weyrich et al. 1997). 

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