Isomerization of n-pentane over platinum promoted tungstated zirconia supported on mesoporous SBA-15 prepared by supercritical impregnation

Tungstated zirconia was supported on mesoporous SBA-15 by impregnation in supercritical ethanol. The resultant catalyst promoted with 1 wt% of Pt shows 100% selectivity of iso-pentane and two times higher conversion in n-pentane isomerization than the one prepared by conventional impregnation. Supercritical impregnation exerts no destruction of the porous silica and offers better dispersion of tungstated zirconia than conventional impregnation. Optimized loading of WO3/ZrO2/SBA-15 is 20/40/40 wt%, which infers to 2.4 W-atoms/nm(2) and 8.9 Zr-atoms/nm(2) dispersed on the SBA-15 support. Moreover, introducing a proper mole fraction of hydrogen in the reactants markedly improves the catalytic activity in n-pentane isomerization. The role of hydrogen was not only served as the reactants, it also acted to regenerate Bronsted acid sites during n-pentane isomerization. However, overdose of hydrogen leaded to a leveling-off in the rate of isomerization and enhanced hydrogenolysis reaction. The in situ IR spectroscopic studies suggested that Bronsted acid sites were the active centers for the isomerization. A reaction mechanism was, therefore, proposed that heterolytic fission of hydrogen and dehydrogenation of n-pentane took place over Pt. The secondary carbocation formed over Bronsted acid sites was rearranged to a tertiary carbocation by methyl migration, followed by reacting with a hydride to generate iso-pentane.

Automated summary

Tungstated zirconia supported on mesoporous SBA-15 through impregnation in supercritical ethanol shows improved catalytic performance in n-pentane isomerization. The optimized loading of WO3/ZrO2/SBA-15 and proper mole fraction of hydrogen in the reactants play crucial roles in enhancing catalytic activity. Additionally, hydrogen not only serves as a reactant but also helps to regenerate active sites during the isomerization process.