Heteropolyacid grafted Pt/Si-MCM-41 catalyst for C ₇ skeletal isomerization

A tungstophosphoric acid grafted Pt/MCM-41 catalyst was synthesized and characterized with several spectroscopic techniques. The Keggin structure of the grafted H ₃PW ₁₂O ₄₀ (referred as HPW) was rather stable after calcination. Highly dispersed HPW created approximately 143 μmol/g Bronsted acid sites with moderate strength. In the n-heptane isomerization reaction, n-heptane conversion over Pt/H ₃PW ₁₂O ₄₀/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.