Acidic solids are used as catalyst at several industrial processes and studies to improve their activities have been developed by different groups. One method well known is sulfating oxide to create new acid sites, but investigations about sulfated niobia are still scarce, This work studied the influence of sulfation on the niobia acidity by using a very simple reaction model, the esterification of acetic acid with ethanol, performed at 60 degrees C and 1 atm. Niobia and sulfated niobia samples were characterized by N-2 adsorption, X-ray diffraction, FTIR and titration with n-butylamine. To investigate the nature of sulfate groups formed on the surface of niobia, calculations based on the Density Functional Theory (DFT) have been performed for two models: pure niobia with hydroxylated surface and sulfated niobia where one OH- surface group was replaced by a HSO4-. The experimental results indicated that the sulfation treatment leads to an increase in the specific surface area, acidity and, consequently, in the activity of niobia, with small changes in the crystal structure of the solid. The presence of sulfate groups was evidenced by FTIR spectra and calculations have indicated HSO4- species bounded to the surface. Density Functional Perturbation Theory (DEPT) was also employed to obtain infrared intensities in the region of sulfate vibration bands. (C) 2016 Elsevier B.V. All rights reserved.