Pt-Re-Sn/Al 2O 3 trimetallic catalysts for naphtha reforming processes without presulfiding step

Abstract

The n-heptane reforming and the cyclopentane hydrogenolysis reactions over noble metal monometallic catalysts (0.3% Pt), bimetallic catalysts (0.3% Pt, x% Re, x = 0.1, 0.3, 0.9 and 2.0, sulfided) and trimetallic catalysts (0.3% Pt, 0.3% Re, y% Sn, y = 0.1, 0.3, 0.6 and 0.9, unsulfided) were studied. The metal function was supported over a chlorided γ-alumina that provided the acid function. The reforming of n-heptane was performed at 450 °C, molar ratio H 2/ n-C 7 = 4 and WHSV = 7.3 while the hydrogenolysis of cyclopentane was performed at 350 °C, H 2/CP = 20 and WHSV = 2.4. The sulfided 0.3Pt-0.3Re catalyst (with 0.06% S) was found to be the best performing bimetallic one. It had a great stability, typical of this kind of catalysts, and also produced a reformate with a high iso-heptanes/toluene ratio. This is advantageous for fulfilling the current environmental regulations that limit the amount of aromatic hydrocarbons in reformulated gasolines. The best trimetallic catalyst was 0.3Pt-0.3Re-0.6Sn which had a similar activity and selectivity as sulfided 0.3Pt-0.3Re, though it displayed a higher stability and a lower hydrogenolysis activity, without the need of presulfidation. Tin affected the metal and acid functions of the catalyst simultaneously and inhibited them to such different degrees that a very convenient metal/acid activity ratio was obtained, resulting in an improvement of the activity, selectivity and stability of the catalysts. It can be concluded that it is possible to prepare trimetallic naphtha reforming catalysts of the Pt-Re-Sn kind with a better performance than conventional sulfided Pt-Re catalysts and with the additional advantage that they do not need complicated sulfiding pretreatments. This simplifies the commercial operation of the reformer unit and enables the application of this catalyst to continuously operated processes.