Hydrogenation of Aromatics in Diesel Fuels on Pt/MCM-41 Catalysts

The hydrogenation activity of Pt supported on two mesoporous MCM-41 samples differing in their chemical composition has been studied by following the kinetics of the hydrogenation of naphthalene at 225–275°C reaction temperature and 5.0 MPa total pressure and by comparing the kinetic parameters obtained with Pt supported on a mesoporous amorphous silica-alumina (MSA) and other conventional supports, such as commercial amorphous silica-alumina (ASA), zeolite USY, γ-alumina, and silica. The two mesoporous MCM-41 and MSA materials having very high surface areas allowed for a better dispersion of the Pt particles, and they showed a superior overall hydrogenation activity as compared to the other supports. However, Pt/USY displayed the highest turnover (activity per exposed surface Pt), owing to the interaction of small Pt aggregates in the supercage of the zeolite with the strong Brönsted acid sites associated to framework aluminum forming electron-deficient Pt species of known enhanced activity. Moreover, both the Al-MCM-41 and USY-based catalysts presented the highest sulfur tolerance during the hydrogenation of a naphthalene feed containing 200 ppm sulfur added as dibenzothiophene. The high metal dispersion and the interaction of the small Pt clusters with the mildly acidic sites present in Al-MCM-41 may account for its high sulfur tolerance. The superior hydrogenation activity and sulfur tolerance of Pt-MCM-41 catalyst observed in the naphthalene experiments were further confirmed during the hydrogenation of a hydrotreated light cycle oil (LCO) feed containing ca 70 wt% aromatics and 400 ppm sulfur.