Isomerization of n-hexane on heteropolyacids supported on SBA-15. 1. Monofunctional impregnated catalysts

• Heteropolyacids supported on SBA-15 are active in isomerization of n-hexane.
• The selectivity towards isomerization products can reach 95%.
• Silicotungstic acid is more selective than phosphotungstic acid.
• The reaction is limited by diffusion.

Monofunctional hybrid materials based on Keggin-type heteropolyacids supported on mesostructured silica were used in isomerization of n-hexane. The heteropolyacids, namely H3PW12O40 or H4SiW12O40, were immobilized onto SBA-15 type silica by incipient wetness impregnation. The resulting catalysts were thoroughly characterized by N2 adsorption–desorption isotherms, XRD, 31P NMR, TGA and FT-IR. These hybrid materials were active for the gas-phase isomerization of n-hexane. Various reaction parameters and catalyst features were investigated: tungsten loading, reaction temperature, contact time, pressure and nature of the polyanion. All results could be explained by a competition of the mono- and bimolecular mechanisms. Supported tungstosilicic acid was intrinsically more selective than phosphotungstic counterpart and should be preferred for applications in isomerization of alkanes. A deactivation of the catalysts was observed due to the poisoning of acid sites by coke formation.

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