•Acid treatment of CNF reduces porosity, specific surface area and impurity content.•Acid modification of CNF increases a concentration of surface functional groups.•This has an influence on adsorptive properties and palladium dispersion in catalysts.•HCl treatment leads to higher Pd dispersion and faster 1,2-DCB adsorption on surface.•This makes Pd/CNF-HCl the most active catalyst of 1,2-DCB hydrodechlorination. Palladium catalysts on the basis of acid treated carbon nanofibers (CNF) were studied. Using physico-chemical methods of investigation (low-temperature nitrogen adsorption–desorption, FTIR spectroscopy and Boehm titration) it has been shown that under the action of HCl and HNO3 there take place a reduction in the specific surface area and the volume of pores and an increase of the concentration of surface functional groups. This has a substantial influence on the adsorptive properties of CNF, the dispersion of palladium and the catalytic activity in the liquid-phase hydrodechlorination of 1,2-dichlorobenzene. The reaction rate was observed to be the highest in the presence of Pd/CNF-HCl. Treatment of CNF by HCl gives the highest dispersion of palladium on the external surface of CNF. There is also an increase in the adsorption capacity for 1,2-dichlorobenzene and a decreased adsorption of the solvents on the surface of the acid-modified CNF.