Heteropolyacid grafted Pt/Si-MCM-41 catalyst for C7 skeletal isomerization

A tungstophosphoric acid grafted Pt/MCM-41 catalyst was synthesized and characterized with several spectroscopic techniques. The Keggin structure of the grafted H3PW12O40 (referred as HPW) was rather stable after calcination. Highly dispersed HPW created approximately 143 μmol/g Brønsted acid sites with moderate strength. In the n-heptane isomerization reaction, n-heptane conversion over Pt/H3PW12O40/MCM-41 catalyst linearly increased from 5.4% to 79.2% as the reaction temperature increased from 220 °C to 320 °C. Below 260 °C, the isomerization selectivity was 100%. At higher temperature, cracking reactions took place, producing n-butane, i-butane, and propane. The ratio of multibranched to monobranched isomers was between 0.60 and 0.85, indicating that mesostructured catalyst exhibits unique shape selectivity in the skeletal isomerization of n-heptane.

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► The Keggin structure of the grafted H3PW12O40 remained very stable at 350 °C.
► The Pt/HPW/Si-MCM-41 exhibits unique shape selectivity in n-C6 isomerisation.
► The ratio of multibranched to monobranched isomers varied between 0.6 and 0.85.