(491f) Comparative Study of the Hydrogenation of Tetralin on Supported Ni, Pt, and Pd Catalysts
Environmental legislation on diesel fuels is increasingly focusing on reduction of sulfur and aromatics content as well as maximum cetane number (CN). Hydrogenation of aromatics alone may not be sufficient to attain the high CN that has been projected for future legislation and further reactions such as selective ring opening of the hydrogenated compounds may be necessary. It has been shown that the two products of the hydrogenation of tetralin, i.e. cis and trans decalin have different reactivities for the subsequent ring-contraction and ring-opening reactions. Trans-decalin is the more stable isomer of the two, but at the same time is much less reactive than cis-decalin. In previous studies, we found that while cis decalin resulted in substantial selectivity to indanes and alkyl-cyclohexanes over HY catalysts, trans-decalin only converted at high temperatures with low selectivity to C10 products. As a result, we have investigated the gas-phase hydrogenation of tetralin over different catalyst to determine the evolution of the cis-to-trans ratio as a function of conversion. In this study alumina-supported Pt, Pd and Ni catalysts were prepared by incipient wetness impregnation and tested in a fixed-bed continuous flow reactor at a total pressure of 300 psi and in the temperature range 250-300?aC. The catalytic activity tests revealed that the relative rates of hydrogenation to cis- and trans-decalin, as well as the cis-trans isomerization were greatly affected by the site competition of decalin with tetralin, which in turn had different significance over the different catalysts. At conversions above 30 %, Ni catalyst yielded the highest cis/trans decalin ratio, but this ratio converged to about the same value as that obtained on Pt as the conversion approached zero. By contrast, the cis/trans ratio was much lower on Pd catalysts at all conversion levels. It is postulated that the cis/trans ratio is a combination of the intrinsic selectivity to each isomer and the isomerization reaction. However, in order to get isomerized, the cis-decalin needs to compete for adsorption sites with tetralin. As a result, the isomerization is a strong function of conversion and the type of catalyst used.
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