FTIR study of the surface complexes of β-picoline, 3-pyridine-carbaldehyde and nicotinic acid on sulfated TiO2 (anatase)

•Sulfate content determines the type, quantity and strength of acidic sites.•Strong Bronsted acid sites result in the dead-end nicotinates formation.•Weakly bound nicotinates on Lewis acid centers transform into nicotinic acid.

Surface complexes of β-picoline, 3-pyridine-carbaldehyde and nicotinic acid on sulfated TiO2 (anatase) containing 0.12 and 6.9 wt.% SO42− were studied using FTIR spectroscopy. The water and β-picoline were used as molecular probes for identification of surface acidity and sulfate species. Depending on SO42− content, FTIR spectra have revealed differences in the type, quantity and strength of acidic sites as well as in the composition and strength of surface complexes of β-picoline, 3-pyridine-carbaldehyde and nicotinic acid. Both samples possess Lewis and Bronsted acidic sites. But only TiO2 (6.9) contains strong Bronsted sites. On this sample the dead-end nicotinates form during 3-pyridine-carbaldehyde transformation while the weakly bound nicotinates on TiO2 (0.12) surface transform into nicotinic acid.

Graphical abstractOn low sulfated TiO2 (SO42− = 0.12 wt.%) weakly bound nicotinates (νas(COO) = 1528 cm−1 and νa(COO) = 1407 cm−1) transform into nicotinic acid (ν(CO) = 1705 cm−1) while on high sulfated TiO2 (SO42− = 6.9 wt.%) strongly bound nicotinates (νas(COO) = 1555 cm−1 and νa(COO) = 1412 cm−1) are dead-end species.Figure optionsDownload full-size imageDownload high-quality image (90 K)Download as PowerPoint slide