IR study of active sites for n-heptane isomerization over MoO3-ZrO2

The property of acidic sites on MoO3-ZrO2 was studied for n-heptane isomerization. A 2,6-lutidine IR study showed that the introduction of MoO3 on ZrO2 partially eliminated the absorbance band at 1605 cm−1 ascribed to Lewis acid sites corresponding to the presence of the monoclinic phase of ZrO2 and developed several Brönsted and Lewis acid sites with different acidic strengths. MoO3-ZrO2 possesses a large number of relatively weak Lewis and Brönsted acid sites as well as strong acid sites. The active protonic acid sites in n-heptane isomerization were formed from molecular hydrogen through a spillover mechanism with the involvement of doublet bands at 1595 and 1580 cm−1 ascribed to the Lewis acid sites corresponding to the presence of the tetragonal phase of ZrO2. No catalytic activity of MoO3-ZrO2 for n-heptane isomerization was observed in the absence of the doublet bands at 1595 and 1580 cm−1 and hydrogen in the gas phase.

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► MoO3-ZrO2 possesses Brönsted and Lewis acid sites with different acidic strength.
► Bands at 1605 and 1590 cm−1 are Lewis acid sites corresponding to monoclinic ZrO2
► Bands at 1595 and 1580 cm−1 are Lewis acid sites corresponding to tetragonal ZrO2.
► Only a doublet bands at 1595 and 1580 cm−1 involved in the formation of H+ from H2.
► No activity was observed in the absence of a doublet bands at 1595 and 1580 cm−1.