Abstract
Support Pt-W catalysts are studied for 3-methylhexane reforming. The increase in tungsten loading and the use of SiO2 support instead of Al2O3 in Pt-W catalysts leads to the decrease in total activity and aromatization selectivity. X-ray Photoelectron Spectroscopy (XPS) has been applied to bimetallic Pt-W/Al2O3 and SiO2 catalysts with different Pt/W ratios to try to explain the catalytic results. Observations lead to the conclusion that tungsten species are strongly anchored on the support in Pt-W/Al2O3 catalysts at low tungsten concentration. In this case, tungsten species are not reducible (oxidation state +VI) and not accessible catalytically; tungsten is hindered by small Pt particles. At large tungsten loadings, beyond the theoretical monolayer capacity of the support, a fraction of tungsten species migrates to the surface and becomes reducible. This fraction of tungsten-reducible species and large platinum particles are accessible on the surface, but another fraction of tungsten species strongly anchored on the support remains not accessible and not reducible. A model is proposed.
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