Pd–Pt catalysts on mesoporous SiO2–Al2O3 with superior activity for HDS of 4,6-dimethyldibenzothiophene: Effect of metal loading and support composition

• Mesoporous SiO2–Al2O3 is promising support of Pd–Pt for HDS of 4,6-DMDBT.
• HDS activity of most of Pd–Pt catalysts correlates with cumene cracking activity.
• Pd–Pt catalyst with 0.1% metals is much more active than CoMo/Al2O3.

Mesoporous silica–aluminas (MSA) containing 2–13 wt.% Al2O3 were studied as supports of Pd–Pt catalysts with total metal content 0.10–1.50 wt.%. Transformation of 4,6-dimethyldibenzothiophene (4,6-DMDBT) was evaluated both on the MSA supports and Pd–Pt/MSA catalysts in a flow reactor in the gas phase at 300 °C and 5 MPa. The catalysts were characterized by nitrogen adsorption, hydrogen chemisorption, cumene cracking activity for Brønsted acidity and some by electron probe microanalysis (EPMA) and transmission electron microscopy/energy dispersive X-ray spectroscopy (TEM/EDS). It was found that isomerization and disproportionation of 4,6-DMDBT occur on MSA supports and increase with the Al2O3 content. This Al2O3 phase had multiple effect on the properties of Pd–Pt catalysts. It controlled their Brønsted acidity and the amount of deposited active metal phase, both these factors consequently influenced the overall HDS activity and HYD/cracking selectivity. HDS on Pd–Pt catalysts proceeded almost exclusively by the hydrogenation (HYD) route and increased with the metal loading. Activities of majority of Pd–Pt catalysts correlated with their Brønsted acidities while not with metal dispersion. Pd–Pt/MSA catalysts were much more active than a conventional sulfide catalyst; the lowest metal loadings around 0.10 wt.% gave still 5–7 time more active catalysts than CoMo/Al2O3. We believe this was achieved due to the ability of mesoporous acidic supports to transform 4,6-DMDBT to more reactive compounds in cooperation with highly active Pd–Pt phase in the following HYD and HDS steps.

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