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

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 degrees C and 5 MPa. The catalysts were characterized by nitrogen adsorption, hydrogen chemisorption, cumene cracking activity for Bronsted 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 Bronsted 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 Bronsted 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. (C) 2015 Elsevier B.V. All rights reserved.