Solid-state MAS NMR studies of sulfonic acid-functionalized SBA-15

Solid-state magic-angle spinning (MAS) nuclear magnetic resonance (NMR) was used to characterize propylsulfonic acid-functionalized SBA-15 materials prepared by the cocondensation method. The propylsulfonic acid-group concentration and distribution was systematically varied from 2.5 to 10%. As a way of coupling two acid sites and controlling the acid site spatial distribution, tethered propylsulfonic acid groups were incorporated into SBA-15. C-13, Si-29 and H-1 MAS NMR were used to determine the extent of functionalization. Probe molecules, such as triethylphosphine oxide and diphenyldiphosphines were used to evaluate acid site strength and acid site distributions, respectively.