Surface complexes of beta-picoline, 3-pyridine-carbaldehyde and nicotinic acid on 20 wt.% V2O5/TiO2 catalysts containing 0.07 and 6.31wt.% SO42- were studied by FTIR spectroscopy and temperature programmed reaction technique. The water (both H2O and D2O), pyridine and beta-picoline were used as molecular probes for identification of surface acidity and the structure of sulfate species. Both samples possess Lewis and Bronsted acidic sites. beta-Picoline, 3-pyridine-carbaldehyde and nicotinic acid form surface complexes of similar structure on both studied catalysts. But high sulfated catalyst contains stronger Bronsted sites in greater amount. It leads to the formation of stronger bound surface complexes of beta-picoline, 3-pyridine-carbaldehyde and nicotinic acid. The strongly bound surface complexes are transformed into by-products (COx, pyridine and 3-cyanopyridine). It resulted in substantial reduction of nicotinic acid yield. (C) 2013 Elsevier B.V. All rights reserved.